Determinants of serum 25 hydroxyvitamin D levels in a nationwide cohort of blacks and non-Hispanic whites

Ambient ultraviolet-B radiation, supplements and other factors interact to impact vitamin D status differently depending on ethnicity: A cross-sectional study

BACKGROUND & AIMS

Many determinants of vitamin D status have been well-described, yet supplementation guidelines largely follow a one-size-for-all model and deficiency remains common. We hypothesised that accounting accurately for ultraviolet-B (UVB) radiation and considering interactions could advance understanding of vitamin D status.

METHODS

Asian, Black, and White participants from the UK Biobank cohort were included (N = 438,978). The Tropospheric Emission Monitoring Internet Service provided UVB data which we linked to participants' place of residence. UVB dose over 135 days prior to blood draw was weighted and added, yielding cumulative and weighted UVB (CW-D-UVB). The association between 25(OH)D and selected variables was assessed in multivariable linear regression models with and without interactions, stratified by ethnicity. Predictors were ranked using standardised β-coefficients.

RESULTS

Median 25(OH)D differed by ethnicity (Asian: 25.4 nmol/L (10.2 ng/mL), Black: 30.6 nmol/L (12.2 ng/mL), White: 47.9 nmol/L (19.2 ng/mL), p-value < 0.001). CW-D-UVB was strongly associated with 25(OH)D in all ethnicities. It was the most important predictor in White (βAsian = 0.15, βBlack = 0.20, βWhite = 0.35), whereas supplementation was in Asian and Black participants (βAsian = 0.30, βBlack = 0.24, βWhite = 0.21). We identified statistically significant interactions between BMI:supplementation (all), CW-D-UVB:sex (Asian and White), and CW-D-UVB:age (Black and White), and in White population between CW-D-UVB and supplementation, BMI, and cholesterol.

CONCLUSION

Vitamin D deficiency was widespread, particularly among non-White individuals. UVB was a strong predictor of 25(OH)D and the effect was modified by other factors. Findings suggest that accurately measured ambient-UVB radiation and interactions could improve 25(OH)D prediction models, and support personalised approaches to vitamin D optimisation.

Association of rs2282679 polymorphism in vitamin D binding protein gene (GC) with the risk of vitamin D deficiency in an iranian population: season-specific vitamin D status

BACKGROUND

Genome-wide association studies in Western countries indicate a considerable impact of variations in vitamin D binding protein (GC) genes on serum concentrations of 25-hydroxyvitamin D (25(OH)D). We aimed to investigate an association between rs2282679 polymorphism in GC and vitamin D deficiency.

METHODS

A cross-sectional study conducted in the framework of the Tehran Cardio-Metabolic Genetic Study (TCGS) cohort. A total of 1568 participants aged > 18 years were randomly selected, and their 25(OH) D concentration was measured. Vitamin D deficiency was assessed concerning rs2282679 by descriptive and multivariate analysis, odds ratio (OR), and 95% confidence intervals (95%CI) calculated. Since the interaction term between rs2282679 and recruitment season was significant, we performed regression analysis separately for individuals whose blood was taken in high sunny and those whose blood was drawn in the low sunny season.

RESULTS

The rs2282679 polymorphism was in Hardy-Weinberg equilibrium (P > 0.05) in the studied population. The serum concentration of 25(OH) D median was 15.0 ng/mL, and the prevalence of VDD was 27.8%. The presence of the G allele in rs2282679 increases the risk of VDD in additive (OR = 1.35, 95% CI: 1.06-1.73) and dominant (OR = 1.33, 95% CI: 1.06-1.68) genetic models. After separating participants based on the recruitment season, the unfavorable association was observed in the additive and dominant only in the low sunny season.

CONCLUSION

The finding of the current study indicates that the GC rs2282679 SNP is associated with vitamin D deficiency. It seems that the impact of risk allele increased in the low sunny season when UV exposure has been declined.

Development and Validation of a Predictive Model of Hypovitaminosis D in General Adult Population: SCOPYD Study

The worldwide global increase in serum 25-hydroxyvitamin D (25(OH)D) measurements has led some countries to restrict reimbursement for certain clinical situations only. Another approach could consist in providing physicians with screening tools in order to better target blood test prescription. The objective of the SCOPYD study was to identify the best combination of predictors of serum VitD concentration among adults aged 18–70 years. Potential risk factors for VitD deficiency were collected using a comprehensive self-administered questionnaire. A multivariable linear regression was used to build a predictive model of serum 25(OH)D concentration. Among 2488 participants, 1080 (43.4%) had VitD deficiency (<50 nmol/L) and 195 (7.8%) had severe deficiency (<25 nmol/L). The final model included sunlight exposure in the preceding week and during the last holidays, month of blood sampling, age, sex, body mass index, skin phototype, employment, smoking, sport practice, latitude, and VitD supplementation in preceding year. The area under the curve was 0.82 (95% CI (0.78; 0.85)) for severe deficiency. The model predicted severe deficiency with a sensitivity of 77.9% (95% CI (69.1; 85.7)) and a specificity of 68.3% (95% CI (64.8; 71.9)). We identified a set of predictors of severe VitD deficiency that are easy to collect in routine that may help to better target patients for serum 25(OH)D concentration determination.

Risk Factors Associated with Vitamin D Status among Older Puerto Rican Adults

BACKGROUND

Vitamin D deficiency has been associated with health problems globally, but there is limited information on vitamin D status and associated risk factors among adults in underserved populations.

OBJECTIVE

This study aimed to identify risk factors for vitamin D deficiency/insufficiency among Puerto Rican adults from the Boston Puerto Rican Health Study (BPRHS).

METHODS

A total of 822 adults (45-75 y, at baseline) were included in these analyses. Deficiency was defined as serum 25-hydroxyvitamin D [25(OH)D] <30 and insufficiency as 30 to <50 nmol/L. Dietary intake was assessed with a validated FFQ. Associations between risk factors, including dietary vitamin D, supplement use, ancestry, skin pigmentation, months in the past year spent in a southern climate, and serum 25(OH)D were assessed with multivariable general linear models.

RESULTS

Approximately 13% of participants were deficient in 25(OH)D and another 43% insufficient. Skin pigment was associated with 25(OH)D using 3 measures, greater African ancestry (β ± SE) (-7.74 ± 2.91, P = 0.01); interviewer assessed dark or medium, compared with white, skin tone, (-5.09 ± 2.19, P = 0.02 and -5.89 ± 1.58, P < 0.001, respectively); and melanin index of the upper inner right arm, assessed using a spectrophotometer (-2.04 ± 0.84, P = 0.02). After adjusting for ancestry, factors associated with lower serum 25(OH)D included smoking (-4.49 ± 1.58, P = 0.01); BMI (-0.21 ± 0.10, P = 0.04); and spring compared with autumn blood draw (-4.66 ± 1.68, P = 0.004). Factors associated with higher serum 25(OH)D included female sex compared with male (4.03 ± 1.58, P = 0.01); dietary vitamin D intake μg/d (0.71 ± 0.25, P < 0.004); vitamin D supplement use (4.50 ± 1.87, P = 0.02); income to poverty ratio (0.01 ± 0.01, P = 0.06), and months in a southern climate during the past year (0.96 ± 0.56, P = 0.09).

CONCLUSIONS

Vitamin D deficiency/insufficiency was prevalent in this Puerto Rican population living in the northeastern USA. Several factors were associated with this, which may assist in identifying those at risk. Interventions are needed to improve serum 25(OH)D concentration, particularly among those with limited exposure to sunlight.

Genetic loci associated with skin pigmentation in African Americans and their effects on vitamin D deficiency

A recent genome-wide association study (GWAS) in African descent populations identified novel loci associated with skin pigmentation. However, how genomic variations affect skin pigmentation and how these skin pigmentation gene variants affect serum 25(OH) vitamin D variation has not been explored in African Americans (AAs). In order to further understand genetic factors that affect human skin pigmentation and serum 25(OH)D variation, we performed a GWAS for skin pigmentation with 395 AAs and a replication study with 681 AAs. Then, we tested if the identified variants are associated with serum 25(OH) D concentrations in a subset of AAs (n = 591). Skin pigmentation, Melanin Index (M-Index), was measured using a narrow-band reflectometer. Multiple regression analysis was performed to identify variants associated with M-Index and to assess their role in serum 25(OH)D variation adjusting for population stratification and relevant confounding variables. A variant near the SLC24A5 gene (rs2675345) showed the strongest signal of association with M-Index (P = 4.0 x 10-30 in the pooled dataset). Variants in SLC24A5, SLC45A2 and OCA2 together account for a large proportion of skin pigmentation variance (11%). The effects of these variants on M-Index was modified by sex (P for interaction = 0.009). However, West African Ancestry (WAA) also accounts for a large proportion of M-Index variance (23%). M-Index also varies among AAs with high WAA and high Genetic Score calculated from top variants associated with M-Index, suggesting that other unknown genomic factors related to WAA are likely contributing to skin pigmentation variation. M-Index was not associated with serum 25(OH)D concentrations, but the Genetic Score was significantly associated with vitamin D deficiency (serum 25(OH)D levels less than 12 ng/mL) (OR, 1.30; 95% CI, 1.04-1.64). The findings support the hypothesis suggesting that skin pigmentation evolved responding to increased demand for subcutaneous vitamin D synthesis in high latitude environments.

Disparities in Head and Neck Cancer: A Case for Chemoprevention with Vitamin D

Blacks experience disproportionate head and neck cancer (HNC) recurrence and mortality compared to Whites. Overall, vitamin D status is inversely associated to HNC pointing to a potential protective linkage. Although hypovitaminosis D in Blacks is well documented it has not been investigated in Black HNC patients. Thus, we conducted a prospective pilot study accessing vitamin D status in newly diagnosed HNC patients stratified by race and conducted in vitro studies to investigate mechanisms associated with potential cancer inhibitory effects of vitamin D. Outcome measures included circulating levels of vitamin D, related nutrients, and risk factor characterization as well as dietary and supplemental estimates. Vitamin D-based in vitro assays utilized proteome and microRNA (miR) profiling. Nineteen patients were enrolled, mean circulating vitamin D levels were significantly reduced in Black compared to White HNC patients, 27.3 and 20.0 ng/mL, respectively. Whites also supplemented vitamin D more frequently than Blacks who had non-significantly higher vitamin D from dietary sources. Vitamin D treatment of HNC cell lines revealed five significantly altered miRs regulating genes targeting multiple pathways in cancer based on enrichment analysis (i.e., negative regulation of cell proliferation, angiogenesis, chemokine, MAPK, and WNT signaling). Vitamin D further altered proteins involved in cancer progression, metastasis and survival supporting a potential role for vitamin D in targeted cancer prevention.

Environmental and Genetic Determinants of Serum 25(OH)-Vitamin D Levels during Pregnancy and Early Childhood

Vitamin D insufficiency has become a common health problem worldwide, particularly among pregnant women and young children. Therefore, we sought to identify environmental, dietary, and genetic determinants of serum 25(OH)-vitamin D (25(OH)D) levels during pregnancy and early childhood. 25(OH)D was measured in women at 24-weeks of gestation (n = 738) and one-week postpartum (n = 284) in the population-based Danish COPSAC₂₀₁₀ mother–child cohort; and in cord blood (n = 257) and age 4 years (n = 298) in children from the at-risk COPSAC₂₀₀₀ mother–child cohort. Environmental, dietary, and genetic variables were tested for association with 25(OH)D using linear regression analyses. After adjusting for season of blood sampling, determinants of lower 25(OH)D levels during pregnancy in the women were higher pre-pregnancy BMI, lower age at birth, lower genetic vitamin D score, lower dietary vitamin D intake, and lower social circumstances. In children, the determinants were lower maternal age at birth, higher pre-pregnancy BMI, lower genetic vitamin D score, older siblings, exposure to tobacco smoking, and female sex. Genetics was an important determinant at all time points, alone explaining 2%–11% of the variance in 25(OH)D. Important determinants of circulating 25(OH)D levels during pregnancy and early childhood include environmental factors, diet, and to a large extent genetics.

Association between Vitamin D Levels and Nonalcoholic Fatty Liver Disease: Potential Confounding Variables

Nonalcoholic fatty liver disease (NAFLD), historically considered to be the hepatic component of the metabolic syndrome, is a spectrum of fat-associated liver conditions, in the absence of secondary causes, that may progress to nonalcoholic steatohepatitis (NASH), fibrosis, and cirrhosis. Disease progression is closely associated with body weight or fatness, dyslipidemia, insulin resistance, oxidative stress, and inflammation. Recently, vitamin D deficiency has been linked to the pathogenesis and severity of NAFLD because of vitamin D "pleiotropic" functions, with roles in immune modulation, cell differentiation and proliferation, and regulation of inflammation. Indeed, several studies have reported an association between vitamin D and NAFLD/NASH. However, other studies have failed to find an association. Therefore, we sought to critically review the current evidence on the association between vitamin D deficiency and NAFLD/NASH, and to analyze and discuss some key variables that may interfere with this evaluation, such as host-, environment-, and heritability-related factors regulating vitamin D synthesis and metabolism; definitions of deficient or optimal vitamin D status with respect to skeletal and nonskeletal outcomes including NAFLD/NASH; methods of measuring 25(OH)D; and methods of diagnosing NAFLD as well as quantifying adiposity, the cardinal link between vitamin D deficiency and NAFLD.

Predicting serum vitamin D concentrations based on self-reported lifestyle factors and personal attributes

Evidence supports the role of vitamin D in various conditions of development and ageing. Serum 25-hydroxyvitamin D (25(OH)D) is the best indicator for current vitamin D status. However, the cost of its measurement can be prohibitive in epidemiological research. We developed and validated multivariable regression models that quantified the relationships between vitamin D determinants, measured through an in-person interview, and serum 25(OH)D concentrations. A total of 200 controls participating in a population-based case-control study in Montreal, Canada, provided a blood specimen and completed an in-person interview on socio-demographic, reproductive, medical and lifestyle characteristics and personal attributes. Serum 25(OH)D concentrations were quantified by liquid chromatography-tandem MS. Multivariable least squares regression was used to build models that predict 25(OH)D concentrations from interview responses. We assessed high-order effects, performed sensitivity analysis using the lasso method and conducted cross-validation of the prediction models. Prediction models were built for users and non-users of vitamin D supplements separately. Among users, alcohol intake, outdoor time, sun protection, dose of supplement use, menopausal status and recent vacation were predictive of 25(OH)D concentrations. Among non-users, BMI, sun sensitivity, season and recent vacation were predictive of 25(OH)D concentrations. In cross-validation, 46-47 % of the variation in 25(OH)D concentrations were explained by these predictors. In the absence of 25(OH)D measures, our study supports that predicted 25(OH)D scores may be used to assign exposure in epidemiological studies that examine vitamin D exposure.

Sex consideration in diet-biomarker-related indices: a systematic review

OBJECTIVE

An index of biomarkers derived from dietary factors (diet-biomarker-related index) identifies foods and nutrients that encompass physiological potentials and provides scientific evidence for dietary patterns that increase the risk of disease associated with specific biomarkers. Although men and women have different dietary patterns and physiological characteristics, sex is not often considered when investigators develop a diet-biomarker-related index. We aimed to review whether epidemiological studies developed diet-biomarker-related indices in a sex-specific way.

DESIGN

We systematically searched for epidemiological studies that developed diet-biomarker-related indices, including (i) biomarker prediction indices that include dietary factors as explanatory variables and (ii) dietary patterns to explain biomarker variations, in the PubMed and EMBASE databases. We qualitatively reviewed the sex consideration in index development.

RESULTS

We identified seventy-nine studies that developed a diet-biomarker-related index. We found that fifty-four studies included both men and women. Of these fifty-four studies, twenty-nine (53·7 %) did not consider sex, eleven (20·3 %) included sex in the development model, seven (13·0 %) considered sex but did not include sex in the development model, and seven (13·0 %) derived a diet-biomarker-related index for men and women separately. A list of selected dietary factors that explained levels of biomarkers generally differed by sex in the studies that developed a diet-biomarker-related index in a sex-specific way.

CONCLUSIONS

Most studies that included both men and women did not develop the diet-biomarker-related index in a sex-specific way. Further research is needed to identify whether a sex-specific diet-biomarker-related index is more predictive of the disease of interest than an index without sex consideration.

Vitamin D: And its role in breast cancer

Vitamin D is a fat soluble vitamin that plays a role in calcium and phosphorus homeostasis. Recently, extensive research on its extraskeletal actions has linked vitamin D deficiency to an increased risk of infection, diabetes mellitus types 1 and 2, cardiovascular disease, obesity, asthma, inflammatory bowel disease, colon, breast, prostate and ovarian cancer and some neurological diseases. There are various mechanisms by which vitamin D influences the natural history of cancer. These include the role of vitamin D in the induction of apoptosis, stimulation of cell differentiation, anti-inflammatory and antiproliferative effects and inhibition of angiogenesis, invasion and metastasis. The aim of this review is to clarify the true role of vitamin D in the onset of breast cancer and evolution of the disease after treatment. A further aim is to suggest new research directions to identify indications and requirements for vitamin D supplementation in patients with breast cancer.

Determinants of Plasma 25-Hydroxyvitamin D Concentrations among Breast Cancer Survivors in Korea

We identified demographic, lifestyle, and clinical factors associated with vitamin D status among breast cancer survivors. The vitamin D prediction model may be a useful surrogate of circulating 25-hydroxvitamin D (25(OH)D) concentrations when this measure was not available. We included a total of 216 Korean breast cancer survivors aged 21–79 years who had been diagnosed with stage I to III primary breast cancer and had breast cancer surgery at least 6 months before enrolment. We used linear and logistic regressions to identify determinants for the plasma 25(OH)D concentrations and vitamin D insufficiency (plasma 25(OH)D concentration < 50 nmol/L). We observed that 48.85% of breast cancer survivors had a plasma 25(OH)D concentration less than 50 nmol/L. We identified the following determinants for plasma 25(OH)D concentrations: time since diagnosis (β = −0.005 for 1 month increment), supplementary vitamin D intake (β = 0.06 for 10 μg/day increment), season of the blood draw (β = 0.35 for summer; β = 0.32 for fall; β = 0.26 for winter vs. spring), smoking status (β = 0.28 for former vs. never), use of any supplement (β = −0.35 for non-use vs. use), and the parity number (β = −0.30 for three or more vs. one) were associated with the plasma 25(OH)D concentrations. In addition to the aforementioned variables, body mass index (BMI) was associated with the prevalence of vitamin D insufficiency. We identified the determinants for the plasma 25(OH)D concentrations among Korean breast cancer survivors. Future studies are needed to investigate the role of vitamin D in the progression of breast cancer among Korean breast cancer survivors.

Prevalence and Predictors of Low Serum 25-Hydroxyvitamin D among Female African-American Breast Cancer Survivors

BACKGROUND

African-American breast cancer survivors commonly demonstrate low serum 25-hydroxyvitamin D (25(OH)D). Decreased cutaneous conversion, high levels of adiposity, and even breast cancer treatment may influence vitamin D status. Previous investigations have analyzed African-American women in aggregate with other breast cancer survivors and have not comprehensively addressed these influential factors.

OBJECTIVES

To determine the prevalence of low serum 25(OH)D in an exclusively African-American cohort of female breast cancer survivors with overweight/obesity and to evaluate the role of ultraviolet (UV) light exposure, body composition, and dietary sources of vitamin D on serum 25(OH)D levels.

DESIGN

Cross-sectional.

PARTICIPANTS

Pre- and postmenopausal African-American breast cancer survivors (n=244) were recruited from various neighborhoods in the city of Chicago, IL, between September 2011 and September 2014 for a larger weight loss trial.

MAIN OUTCOME MEASURES

Demographic, clinical, anthropometric (body mass index [calculated as kg/m²], waist circumference, and hip circumference), blood specimen, dietary intake (food frequency questionnaire), and sun behavior data were collected by trained study personnel before trial participation. Dual-energy x-ray absorptiometry was used to quantify adiposity (total, percentage, regional, visceral) and lean mass. Serum 25(OH)D was used as the biomarker reflective of vitamin D status.

STATISTICAL ANALYSES

Mean (±standard deviation), frequencies, and multivariate linear regression modeling.

RESULTS

The average participant was 57.4 years old (±10.0), 6.9 years (±5.2) from initial breast cancer diagnosis with a body mass index of 36.2 (±6.2). The majority of participants (60%) reported habitual oral vitamin D supplementation with mean intake of 327 IU (±169). Vitamin D deficiency was prevalent in 81% and 43%, when the cut points of the Endocrine Society (<30 ng/mL or <75 nmol/L) and the Institute of Medicine (<20 ng/mL or <50 nmol/L) were applied, respectively. A multivariate model adjusting for age, seasonality of blood draw, total energy intake, use of supplemental vitamin D, darker skin pigmentation, breast cancer stage, and waist-to-hip ratio was able to explain 28.8% of the observed variance in serum 25(OH)D concentrations. No significant associations were detected for body mass index or any dual-energy x-ray absorptiometry measures of body composition.

CONCLUSIONS

Considering the number of women who endorsed use of vitamin D supplementation, the prevalence of vitamin D deficiency among these African-American breast cancer survivors was high. Vitamin D supplementation, sun behavior, and waist-to-hip ratio may serve as future points of intervention to improve the vitamin D status of this minority survivor population.

Vitamin D Binding Protein and Vitamin D Levels in Multi-Ethnic Population

INTRODUCTION

Low levels of 25-hydroxyvitamin D (25(OH)D) has been associated with many negative health outcomes including falls and fractures. 25(OH)D is largely bound to vitamin D binding protein (VDBP). There is increasing evidence that free or bioavailable 25(OH)D may be a better measure of vitamin D deficiency.

OBJECTIVE

To determine the prevalence of 25(OH)D deficiency and VDBP levels in multi-ethnic population, and its impact on muscle strength.

DESIGN AND METHODS

Cross-sectional study of older adults in Western region of Singapore. 295 participants from three ethnic groups were selected from the Healthy Older People Everyday (HOPE) cohort for measurements of total 25(OH)D and VDBP levels. Total 25(OH)D, VDBP, frailty status, Timed-Up-and-Go (TUG) and grip strength (GS) were assessed. Albumin, free and bioavailable 25(OH)D were only available for 256 participants.

RESULTS

53% of Malay and 55% of Indians were deficient in 25(OH)D compared with 18.2% of ethnic Chinese participants. Chinese also had higher total 25(OH)D concentrations with a mean of 29.1 ug/l, (p = <0.001). Chinese had the lowest level of VDBP (169.6ug/ml) followed by Malay (188.8 ug/ml) and Indian having the highest (220.1 ug/ml). Calculated bioavailable and free 25(OH)D levels were significantly higher in Chinese, followed by Malays and Indians, which also correlated with better grip strength measures amongst the Chinese.

CONCLUSION

The Malays and Indians had overall lower free, bioavailable and total 25(OH)D compared with ethnic Chinese. Chinese ethnic group also had the lowest VDBP and better overall grip strength.

Predictors of 25-Hydroxyvitamin D Concentration Measured at Multiple Time Points in a Multiethnic Population

The evidence for a relationship between serum vitamin D levels and nonskeletal health outcomes is inconsistent. The validity of single or predicted measurements of 25-hydroxyvitamin D (25(OH)D) concentration is unknown, as levels of this biomarker are highly seasonally variable. We compared models of 25(OH)D measured at baseline, at multiple time points throughout the year, and averaged over the year among 309 persons in Toronto, Ontario, Canada (43°N latitude) during 2009-2013. Information and blood samples were collected every 2 months. Baseline and average 25(OH)D concentrations were correlated (r = 0.88). Major factors associated with 25(OH)D level were similar across models and included race/ethnicity (concentrations in non-European groups were lower than those in Europeans), vitamin D supplement use of ≥1,000 IU/day (18.9 nmol/L (95% confidence interval (CI): 16.1, 21.8) vs. no supplement use in a full data set with all factors), and the presence of the group-specific component/vitamin D binding protein gene (GC/DBP) rs4588 functional polymorphism (AA vs. CC: -16.7 nmol/L (95% CI: -26.2, -7.1); CA vs. CC: -10.7 nmol/L (95% CI: -14.9, -6.5)). Most factors had similar associations in Europeans and non-Europeans. Genetic factors may play a greater role in average 25(OH)D concentrations. Prediction models for 25(OH)D are challenging and population-specific, but use of genetic factors along with a few common population-relevant, quantifiable nongenetic factors with strong associations may be the most feasible approach to vitamin D assessment over time.

Self-Report Dietary Assessment Tools Used in Canadian Research: A Scoping Review

Choosing the most appropriate dietary assessment tool for a study can be a challenge. Through a scoping review, we characterized self-report tools used to assess diet in Canada to identify patterns in tool use and to inform strategies to strengthen nutrition research. The research databases Medline, PubMed, PsycINFO, and CINAHL were used to identify Canadian studies published from 2009 to 2014 that included a self-report assessment of dietary intake. The search elicited 2358 records that were screened to identify those that reported on self-report dietary intake among nonclinical, non-Aboriginal adult populations. A pool of 189 articles (reflecting 92 studies) was examined in-depth to assess the dietary assessment tools used. Food-frequency questionnaires (FFQs) and screeners were used in 64% of studies, whereas food records and 24-h recalls were used in 18% and 14% of studies, respectively. Three studies (3%) used a single question to assess diet, and for 3 studies the tool used was not clear. A variety of distinct FFQs and screeners, including those developed and/or adapted for use in Canada and those developed elsewhere, were used. Some tools were reported to have been evaluated previously in terms of validity or reliability, but details of psychometric testing were often lacking. Energy and fat were the most commonly studied, reported by 42% and 39% of studies, respectively. For ∼20% of studies, dietary data were used to assess dietary quality or patterns, whereas close to half assessed ≤5 dietary components. A variety of dietary assessment tools are used in Canadian research. Strategies to improve the application of current evidence on best practices in dietary assessment have the potential to support a stronger and more cohesive literature on diet and health. Such strategies could benefit from national and global collaboration.

Predicted 25-hydroxyvitamin D in relation to incidence of breast cancer in a large cohort of African American women

BACKGROUND

Vitamin D deficiency, which has been linked to an increased risk of colorectal cancer, is particularly common among African Americans. Previous studies of vitamin D status and breast cancer risk, mostly conducted in white women, have had conflicting results. We examined the relationship between predicted vitamin D status and incidence of breast cancer in a cohort of 59,000 African American women.

METHODS

Participants in the Black Women's Health Study have been followed by biennial mail questionnaires since 1995, with self-reported diagnoses of cancer confirmed by hospital and cancer registry records. Repeated five-fold cross-validation with linear regression was used to derive the best 25-hydroxyvitamin D (25(OH)D) prediction model based on measured 25(OH)D in plasma specimens obtained from 2856 participants in 2013-2015 and questionnaire-based variables from the same time frame. In the full cohort, including 1454 cases of incident invasive breast cancer, Cox proportional hazards models were used to compute the incidence rate ratio (IRR) for each quartile of predicted vitamin D score relative to the highest quartile. Predicted vitamin D score for each two-year exposure period was a cumulative average of predicted scores from all exposure periods up to that time.

RESULTS

Twenty-two percent of women with measured 25(OH)D were categorized as "deficient" (<20 ng/mL) and another 25 % as "insufficient" (20-29 ng/mL). The prediction model explained 25 % of variation in measured 25(OH)D and the correlation coefficient for predicted versus observed 25(OH)D averaged across all cross-validation runs was 0.49 (SD 0.026). Breast cancer risk increased with decreasing quartile of predicted 25(OH)D, p for trend 0.015; the IRR for the lowest versus highest quartile was 1.23 (95 % confidence interval 1.04, 1.46).

CONCLUSIONS

In prospective data, African American women in the lowest quartile of cumulative predicted 25(OH)D were estimated to have a 23 % increased risk of breast cancer relative to those with relatively high levels. Preventing vitamin D deficiency may be an effective means of reducing breast cancer incidence in African American women.

Free vitamin D does not vary through the follicular phase of the menstrual cycle

The importance of vitamin D (25OHD) in general health and reproductive success has been a focus in the setting of the 25OHD deficiency epidemic. However, there are challenges to understanding 25OHD's effects. The free and bioavailable levels are affected by 25OHD binding protein (DBP) and it is not known how estradiol fluctuations during the menstrual cycle affect these binding parameters. This may impact the most appropriate time to measure 25OHD when determining deficiency. This study characterizes 25OHD throughout the follicular phase of the menstrual cycle. Patients undergoing natural cycle IVF were included. Serum was drawn throughout the follicular phase of the menstrual cycle; 25OHD, DBP, albumin, and estrogen levels were determined for each time point allowing for mathematical calculation of free and bioavailable 25OHD. Early, mid, and late follicular phases were designated by estrogen tertiles among patients. Mean Levels of 25OHD (total, free, bioavailable) and DBP for each tertile were compared with Kruskil-Wallis test for non-parametric groups. Linear regression with GEE was employed due to repeated measures within participants. A total of 33 patients were included with 202 total serum measurements. There was no difference in mean levels of 25OHD (p = 0.77), free 25OHD (p = 0.91), and bioavailable 25OHD (p = 0.76) when measured throughout the follicular phase of the menstrual cycle. Vitamin D metabolism does not fluctuate as estradiol changes in the follicular phase of the menstrual cycle. This data indicates that assessment of 25OHD, in particular when assessed for associations with reproductive outcomes, can be measured reliably at any point during the follicular phase of the menstrual cycle.

25-hydroxyvitamin D status of pregnant women is associated with the use of antenatal vitamin supplements and ambient ultraviolet radiation

Previous research suggests prevalent vitamin D deficiency in pregnant women residing in South Australia and the Eastern Seaboard, however recent data from Perth, Western Australia (WA) is lacking. This cross-sectional study ofn=209 pregnant women (36–40 weeks of gestation, 84% white Caucasian) reports on the vitamin D (25[OH]D) status of a contemporary population of pregnant women in Perth, WA, with a focus on the relative contributions of supplemental vitamin D and ambient ultraviolet (UV) radiation to 25(OH)D levels. Mean (SD) season-adjusted 25(OH)D levels were 77.7 (24.6) nmol/l. The prevalence of vitamin D deficiency (25[OH]D<50 nmol/l) was 13.9%. Ambient UV radiation levels in the 90 days preceding blood draw were significantly correlated with serum 25(OH)D levels (unstandardized coefficient 2.82; 95% CI 1.77, 3.86,P<0.001). Vitamin D supplementation expressed as dose per kg of body weight was also positively correlated with serum 25(OH)D levels (unstandardized coefficient 0.744; 95% CI 0.395, 1.092,P<0.001). In conclusion, this study finds that vitamin D deficiency in a predominantly white Caucasian cohort of pregnant women is less prevalent than has been reported in other studies, providing useful information relating to supplementation and screening in this, and similar, populations.

Vitamin D and Immune Response: Implications for Prostate Cancer in African Americans

Prostate cancer (PCa) is the most common cancer among men in the U.S. African American (AA) men have a higher incidence and mortality rate compared to European American (EA) men, but the cause of PCa disparities is still unclear. Epidemiologic studies have shown that vitamin D deficiency is associated with advanced stage and higher tumor grade and mortality, while its association with overall PCa risk is inconsistent. Vitamin D deficiency is also more common in AAs than EAs, and the difference in serum vitamin D levels may help explain the PCa disparities. However, the role of vitamin D in aggressive PCa in AAs is not well explored. Studies demonstrated that the active form of vitamin D, 1,25-dihydroxyvitamin D, has anti-inflammatory effects by mediating immune-related gene expression in prostate tissue. Inflammation also plays an important role in PCa pathogenesis and progression, and expression of immune-related genes in PCa tissues differs significantly between AAs and EAs. Unfortunately, the evidence linking vitamin D and immune response in relation to PCa is still scarce. This relationship should be further explored at a genomic level in AA populations that are at high risk for vitamin D deficiency and fatal PCa.

VITAMIN D-BINDING PROTEIN IN HEALTHY PRE- AND POSTMENOPAUSAL WOMEN: RELATIONSHIP WITH ESTRADIOL CONCENTRATIONS

OBJECTIVE

To examine the relationship between endogenous serum estradiol and vitamin D-binding protein (DBP) and total, free, and bioavailable 25-hydroxyvitamin D (25OHD) concentrations in pre- and postmenopausal women.

METHODS

In 165 healthy women (ages, 26 to 75 years) not taking any form of exogenous estrogen, the serum concentrations of estradiol, 25OHD, DBP, parathyroid hormone, and albumin were measured. Free and bioavailable 25OHD (free + albumin-bound) levels were calculated from total 25OHD, DBP, and serum albumin levels.

RESULTS

Premenopausal women had higher serum 25OHD (31.5 ± 7.9 ng/mL), DBP (45.3 ± 6.2 mg/dL), and estradiol (52.8 ± 35.0 pg/mL) levels than postmenopausal women (26.5 ± 4.9 ng/mL, 41.7 ± 5.7 mg/dL, and 12.9 ± 4.9 pg/mL), respectively. In addition, the calculated free and bioavailable 25OHD levels were higher in pre- than postmenopausal women (P<.05). Serum estradiol correlated with DBP (r = 0.22; P<.01) and total 25OHD (r = 0.27; P<.01). In multivariate regression models (with or without serum 25OHD), estradiol was independently associated with DBP (P<.05).

CONCLUSION

Lower estradiol level is one of the factors that contribute to lower DBP levels in older women. Our data indicate that besides well-known factors such as age, gender, and race, serum estradiol concentrations are also a physiologic predictor of DBP concentration.

Genetic and environmental factors are associated with serum 25-hydroxyvitamin D concentrations in older African Americans

BACKGROUND

Low circulating 25-hydroxyvitamin D [25(OH)D] is prevalent in African Americans, but predictors of vitamin D status are understudied compared to Caucasian populations.

OBJECTIVE

We investigated whether certain environmental and genetic factors are predictors of circulating 25(OH)D in 989 elderly African Americans participating in the Health, Aging, and Body Composition (Health ABC) Study.

METHODS

Regression analysis estimated the cross-sectional association of nongenetic (environmental) factors with 25(OH)D. Single nucleotide polymorphisms (SNPs) associated with 25(OH)D in Caucasian genome-wide association studies (GWASs) were analyzed for association with serum 25(OH)D, including analyses of all imputed SNPs in identified genomic regions. Genome-wide complex trait analysis (GCTA) evaluated the association of all (genome-wide) genotyped SNPs with serum 25(OH)D in the Health ABC Study with replication in the Multi-Ethnic Study of Atherosclerosis (MESA) cohort.

RESULTS

Gender, study site, season of blood draw, body mass index, dietary supplement use, dairy and cereal consumption, Healthy Eating Index score, and walking >180 min/wk were associated with 25(OH)D (P < 0.05), jointly explaining 25% of the variation in circulating 25(OH)D. Multivitamin supplement use was the strongest predictor of circulating 25(OH)D, and supplement users had a 6.3-μg/L higher serum 25(OH)D concentration compared with nonusers. Previous GWAS-identified gene regions were not replicated in African Americans, but the nonsynonymous rs7041 SNP in group-specific component (vitamin D binding protein) was close to significance thresholds (P = 0.08), and there was evidence for an interaction between this SNP and use of multivitamin supplements in relation to serum 25(OH)D concentration (P = 0.04). Twenty-three percent (95% CI: 0%, 52%) of the variation in serum 25(OH)D was explained by total genetic variation in a pooled GCTA of 2087 Health ABC Study and MESA African-American participants, but population substructure effects could not be separated from other genetic influences.

CONCLUSIONS

Modifiable dietary and lifestyle predictors of serum 25(OH)D were identified in African Americans. GCTA confirms that a proportion of 25(OH)D variability is attributable to genetic variation, but genomic regions associated with the 25(OH)D phenotype identified in prior GWASs of European Americans were not replicated in the Health ABC Study in African Americans.

Winter 25-hydroxyvitamin D levels in young urban adults are affected by smoking, body mass index and educational level

BACKGROUND/OBJECTIVES

To study the relationship of winter 25-hydroxycholecalciferol (25-OHD) levels with age, education, place of residency, marital status and body mass index (BMI) as they may affect sun exposure, vitamin D synthesis and metabolism.

SUBJECTS/METHODS

Subjects (1952) answered a structured questionnaire concerning education, marital status and smoking; and body weight/height, and parathyroid hormone and 25-OHD were measured.

RESULTS

25-OHD levels were higher in the males with elementary and secondary education compared with higher education (46.8±18.5 and 43.7±16 vs 39.9±15.3 nmol/l, P<0.01). Vitamin D deficiency was more prevalent (16.7%, (13.1-20.2) vs 10.8%, (8.4-13.2), P=0.08) and sufficiency was less prevalent (24.6% (20-29.2) vs 33.7%, (29.5-37.8), P=0.005) in those with higher than secondary education. No differences were found among the females. Male smokers had lower 25-OHD than nonsmokers (40.2±16.6 vs 43.6±15.7 nmol/l, P=0.004). Deficiency was more prevalent in the male smokers than nonsmokers with secondary and higher education (secondary 16.6%, (10.1-22.4) vs 8.2%, (5.1-11.3), P=0.006; higher 27.4%, (17.7-37.1) vs 13.2%, (9.0-17.5), P=0.003). 25-OHD was lower in the obese than in the normal-weight females (34.6±16.2 vs 38.2±17.8 nmol/l, analysis of variance, P=0.014), but not males. Marital status was not related to 25-OHD. Only in the urban residents, increasing BMI in the young females increased the risk for vitamin D deficiency by 1%, and smoking had an odds ratio of 1.99 (1.05-3.78) in the young and 2.5 (1.07-5.75) in the middle-aged males.

CONCLUSIONS

Smoking and higher education in the males and obesity in the females were factors for vitamin D deficiency among Bulgarian urban population.

Common vitamin D pathway gene variants reveal contrasting effects on serum vitamin D levels in African Americans and European Americans

Vitamin D deficiency is more common among African Americans (AAs) than among European Americans (EAs), and epidemiologic evidence links vitamin D status to many health outcomes. Two genome-wide association studies (GWAS) in European populations identified vitamin D pathway gene single-nucleotide polymorphisms (SNPs) associated with serum vitamin D [25(OH)D] levels, but a few of these SNPs have been replicated in AAs. Here, we investigated the associations of 39 SNPs in vitamin D pathway genes, including 19 GWAS-identified SNPs, with serum 25(OH)D concentrations in 652 AAs and 405 EAs. Linear and logistic regression analyses were performed adjusting for relevant environmental and biological factors. The pattern of SNP associations was distinct between AAs and EAs. In AAs, six GWAS-identified SNPs in GC, CYP2R1, and DHCR7/NADSYN1 were replicated, while nine GWAS SNPs in GC and CYP2R1 were replicated in EAs. A CYP2R1 SNP, rs12794714, exhibited the strongest signal of association in AAs. In EAs, however, a different CYP2R1 SNP, rs1993116, was the most strongly associated. Our models, which take into account genetic and environmental variables, accounted for 20 and 28 % of the variance in serum vitamin D levels in AAs and EAs, respectively.

Serum 25(OH)D and vitamin D status in relation to VDR, GC and CYP2R1 variants in Chinese

Previous studies have identified several common genetic variants in VDR, GC and CYP2R1 to be associated with circulating levels of 25-hydroxyvitamin D [25(OH)D] and vitamin D deficiency in Western populations. We aimed to investigate the associations of these variants with serum levels of 25(OH)D and vitamin D status in 1,199 Chinese. Nine common variants of VDR, GC and CYP2R1 were genotyped using multiple SNaPshot assay, and serum 25(OH)D was detected by radioimmunoassay. The prevalence of vitamin D deficiency (<50 nmol/L) was 38.8%, which is higher in women (46.2%) than in men (34.3%, P<0.0001). The risk alleles of three common variants of GC (rs7041, rs4588, and rs2282679) were significantly associated with a lower serum levels of 25(OH)D (-1.789 ≤β ≤-3.549, P ≤0.006), while common variants in VDR and CYP2R1 were not associated with serum levels of 25(OH)D after adjusted for covariates (P ≥0.30). None of the nine common variants were associated with the presence of vitamin D deficiency in multivariable adjusted logistic regression analyses (P ≥0.17). Haplotype-based analyses of GC-rs7041 and rs4588 showed that the haplotype Gc2-2 (rs7041 AA and rs4588 TT) had the lowest levels of 25(OH)D compared with other haplotypes that contained at least one copy of Gc1 allele (Ptrend <0.0001). Our results suggest that the common variants of GC are genetic determinants of serum 25(OH)D in Chinese.

A novel approach for prediction of vitamin d status using support vector regression

BACKGROUND

Epidemiological evidence suggests that vitamin D deficiency is linked to various chronic diseases. However direct measurement of serum 25-hydroxyvitamin D (25(OH)D) concentration, the accepted biomarker of vitamin D status, may not be feasible in large epidemiological studies. An alternative approach is to estimate vitamin D status using a predictive model based on parameters derived from questionnaire data. In previous studies, models developed using Multiple Linear Regression (MLR) have explained a limited proportion of the variance and predicted values have correlated only modestly with measured values. Here, a new modelling approach, nonlinear radial basis function support vector regression (RBF SVR), was used in prediction of serum 25(OH)D concentration. Predicted scores were compared with those from a MLR model.

METHODS

Determinants of serum 25(OH)D in Caucasian adults (n = 494) that had been previously identified were modelled using MLR and RBF SVR to develop a 25(OH)D prediction score and then validated in an independent dataset. The correlation between actual and predicted serum 25(OH)D concentrations was analysed with a Pearson correlation coefficient.

RESULTS

Better correlation was observed between predicted scores and measured 25(OH)D concentrations using the RBF SVR model in comparison with MLR (Pearson correlation coefficient: 0.74 for RBF SVR; 0.51 for MLR). The RBF SVR model was more accurately able to identify individuals with lower 25(OH)D levels (<75 nmol/L).

CONCLUSION

Using identical determinants, the RBF SVR model provided improved prediction of serum 25(OH)D concentrations and vitamin D deficiency compared with a MLR model, in this dataset.

Predicting vitamin D deficiency in older Australian adults

OBJECTIVE

There has been a dramatic increase in vitamin D testing in Australia in recent years, prompting calls for targeted testing. We sought to develop a model to identify people most at risk of vitamin D deficiency.

DESIGN AND PARTICIPANTS

This is a cross-sectional study of 644 60- to 84-year-old participants, 95% of whom were Caucasian, who took part in a pilot randomized controlled trial of vitamin D supplementation.

MEASUREMENTS

Baseline 25(OH)D was measured using the Diasorin Liaison platform. Vitamin D insufficiency and deficiency were defined using 50 and 25 nmol/l as cut-points, respectively. A questionnaire was used to obtain information on demographic characteristics and lifestyle factors. We used multivariate logistic regression to predict low vitamin D and calculated the net benefit of using the model compared with 'test-all' and 'test-none' strategies.

RESULTS

The mean serum 25(OH)D was 42 (SD 14) nmol/1. Seventy-five per cent of participants were vitamin D insufficient and 10% deficient. Serum 25(OH)D was positively correlated with time outdoors, physical activity, vitamin D intake and ambient UVR, and inversely correlated with age, BMI and poor self-reported health status. These predictors explained approximately 21% of the variance in serum 25(OH)D. The area under the ROC curve predicting vitamin D deficiency was 0·82. Net benefit for the prediction model was higher than that for the 'test-all' strategy at all probability thresholds and higher than the 'test-none' strategy for probabilities up to 60%.

CONCLUSION

Our model could predict vitamin D deficiency with reasonable accuracy, but it needs to be validated in other populations before being implemented.

Dietary, lifestyle, and genetic determinants of vitamin D status: a cross-sectional analysis from the European Prospective Investigation into Cancer and Nutrition (EPIC)-Germany study

PURPOSE

Considerable variation in 25-hydroxyvitamin D (25(OH)D) in populations worldwide that seems to be independent of latitude has been reported. Therefore, we aimed to assess vitamin D status of a mid-aged German general population and to identify its dietary, lifestyle, anthropometric, and genetic determinants.

METHODS

25(OH)D concentrations were measured by LC-MS/MS in plasma samples of a random subcohort of the German arm of the European Prospective Investigation into Cancer and Nutrition (EPIC) comprising 2,100 subjects aged 35-65 years. Associations between potential predictors and 25(OH)D were assessed by linear regression models.

RESULTS

32.8% of the variance in 25(OH)D was explained by a multivariable regression model, with season being the by far strongest predictor (semi-partial R²: 14.6%). Sex, waist circumference, leisure time physical activity, smoking, polymorphisms in the GC, CYP2R1, and DHCR7 genes, supplement use, exogenous hormone use, alcohol consumption, egg consumption, and fish consumption were significantly associated with 25(OH)D concentrations as well. However, none of these factors explained >2.3% of the variance in 25(OH)D.

CONCLUSION

Even with a comprehensive set of genetic, anthropometric, dietary, and lifestyle correlates, not more than 32.8% of the variation in 25(OH)D could be explained in the EPIC-Germany study, implying that vitamin D prediction scores may not provide an appropriate proxy for measured 25(OH)D. Food intake was only a weak predictor of 25(OH)D concentrations, while a strong seasonal fluctuation in 25(OH)D was shown.

Increased plasma concentrations of vitamin D metabolites and vitamin D binding protein in women using hormonal contraceptives: a cross-sectional study

Use of hormonal contraceptives (HC) may influence total plasma concentrations of vitamin D metabolites. A likely cause is an increased synthesis of vitamin D binding protein (VDBP). Discrepant results are reported on whether the use of HC affects free concentrations of vitamin D metabolites.

AIM

In a cross-sectional study, plasma concentrations of vitamin D metabolites, VDBP, and the calculated free vitamin D index in users and non-users of HC were compared and markers of calcium and bone metabolism investigated.

RESULTS

75 Caucasian women aged 25-35 years were included during winter season. Compared with non-users (n = 23), users of HC (n = 52) had significantly higher plasma concentrations of 25-hydroxyvitamin D (25OHD) (median 84 interquartile range: [67-111] vs. 70 [47-83] nmol/L, p = 0.01), 1,25-dihydroxyvitamin D (1,25(OH)2D) (198 [163-241] vs. 158 [123-183] pmol/L, p = 0.01) and VDBP (358 [260-432] vs. 271 [179-302] µg/mL, p < 0.001). However, the calculated free indices (FI-25OHD and FI-1,25(OH)2D) were not significantly different between groups (p > 0.10). There were no significant differences in indices of calcium homeostasis (plasma concentrations of calcium, parathyroid hormone, and calcitonin, p > 0.21) or bone metabolism (plasma bone specific alkaline phosphatase, osteocalcin, and urinary NTX/creatinine ratio) between groups.

IN CONCLUSION

Use of HC is associated with 13%-25% higher concentrations of total vitamin D metabolites and VDBP. This however is not reflected in indices of calcium or bone metabolism. Use of HC should be considered in the interpretation of plasma concentrations vitamin D metabolites.

Bone metabolism in children and adolescents: main characteristics of the determinants of peak bone mass

The remodelling process of bone acted by osteoblastic and osteoclastic cells allows the tissue to maintain its integrity and mechanical properties. Systemic factors, such as hormonal status, nutrition, physical inactivity, exposure to smoking, alcohol, or particular drugs, as well as a local variation in the load, can influence bone turnover, and consequently, bone mass. In this paper, physical and biochemical factors are described, which are crucially important during the period of growth, i.e. childhood and adolescence, for the construction of a healthy bone.

Relationship of vitamin D levels to blood pressure in a biethnic population

BACKGROUND AND AIMS

Accumulating epidemiological and clinical studies have suggested that vitamin D insufficiency may be associated with hypertension. Blacks tend to have lower vitamin D levels than Whites, but it is unclear whether this difference explains the higher blood pressure (BP) observed in Blacks in a population with healthy lifestyle practices.

METHODS AND RESULTS

We examined cross-sectional data in the Adventist Health Study-2 (AHS-2), a cohort of non-smoking, mostly non-drinking men and women following a range of diets from vegan to non-vegetarian. Each participant provided dietary, demographic, lifestyle and medical history data. Measurements of weight, height, waist circumference, percent body fat and blood pressure and fasting blood samples were obtained from a randomly selected non-diabetic sample of 284 Blacks and 284 Whites aged 30-95 years. Multiple regression analyses were used to assess independent relationships between blood pressure and 25(OH)D levels. Levels of 25(OH)D were inversely associated with systolic BP in Whites after control for age, gender, BMI, and use of BP-lowering medications (β-coefficient -0.23 [95% CI, -0.43, -0.03; p = 0.02]). This relationship was not seen in Blacks (β-coefficient 0.08 [95% CI, -0.14, 0.30; p = 0.4]). Results were similar when controlling for waist circumference or percentage body fat instead of BMI. No relationship between serum 25(OH)D and diastolic BP was seen.

CONCLUSION

Systolic BP is inversely associated with 25(OH)D levels in Whites but not in Blacks. Vitamin D may not be a major contributor to the White-Black differential in BP.

Plasma vitamin D levels, menopause, and risk of breast cancer: dose-response meta-analysis of prospective studies

Previous evidence suggests that higher circulating 25-hydroxyvitamin D (25[OH]D) levels are variably associated with lower breast cancer risk; however, prospective studies and clinical trials have been inconsistent, particularly between older and younger women of differing menopausal status. We conducted a quantitative nonlinear dose-response meta-analysis of prospective studies evaluating the association between circulating 25(OH)D and breast cancer risk, stratified by menopause. A systematic search of MEDLINE and EMBASE included studies published through May 2011. We reviewed references from retrieved articles and contacted relevant investigators for additional data from prospective studies on circulating 25(OH)D levels and incident breast cancers. Prospective studies of circulating vitamin D and breast cancer risk were reviewed, and no language restrictions were imposed. Information on study population, menopausal status, 25(OH)D levels, and relative risk (RR) estimates were extracted using a standardized protocol.A total of 9 prospective studies were included, comprising 5206 cases and 6450 controls. Data were pooled using dose-response random-effects meta-regression models. Identifying nonlinear effects, spline models were optimized for thresholds. The relationship between circulating 25(OH)D and breast cancer risk differed by menopausal status (p = 0.05 for effect modification). While no association was found in premenopausal women, dose-response modeling revealed a nonlinear inverse association among postmenopausal women. Notably, a flat association was observed in the lowest range of 25(OH)D levels <27 ng/mL (RR = 1.01 per 5 ng/mL; 95% confidence interval [CI], 0.98-1.04). In contrast, postmenopausal breast cancer risk decreased with 25(OH)D levels 27-<35 ng/mL (p = 0.02 for nonlinear risk change), where a 5 ng/mL increase in 25(OH)D was associated with a 12% lower risk of breast cancer (RR = 0.88 per 5 ng/mL; 95% CI, 0.79-0.97), with suggestive flattening at higher doses >35 ng/mL. The significant inverse association did not appear to vary across strata of invasive/in-situ cases, body mass index adjustment, region, postmenopausal hormone use, or assay method.In summary, this dose-response meta-analysis of prospective studies of plasma 25(OH)D suggested a breast cancer risk differential by menopause, whereby a step-wise inverse association was observed beyond a threshold of 27 ng/mL, but with flattening of effects above 35 ng/mL, in postmenopausal women. These findings help resolve prior inconsistent findings and may carry important clinical and public health implications.

Sunlight and other determinants of circulating 25-hydroxyvitamin D levels in black and white participants in a nationwide U.S. study

Circulating 25-hydroxyvitamin D (25(OH)D), a marker for vitamin D status, is associated with bone health and possibly cancers and other diseases; yet, the determinants of 25(OH)D status, particularly ultraviolet radiation (UVR) exposure, are poorly understood. Determinants of 25(OH)D were analyzed in a subcohort of 1,500 participants of the US Radiologic Technologists (USRT) Study that included whites (n = 842), blacks (n = 646), and people of other races/ethnicities (n = 12). Participants were recruited monthly (2008-2009) across age, sex, race, and ambient UVR level groups. Questionnaires addressing UVR and other exposures were generally completed within 9 days of blood collection. The relation between potential determinants and 25(OH)D levels was examined through regression analysis in a random two-thirds sample and validated in the remaining one third. In the regression model for the full study population, age, race, body mass index, some seasons, hours outdoors being physically active, and vitamin D supplement use were associated with 25(OH)D levels. In whites, generally, the same factors were explanatory. In blacks, only age and vitamin D supplement use predicted 25(OH)D concentrations. In the full population, determinants accounted for 25% of circulating 25(OH)D variability, with similar correlations for subgroups. Despite detailed data on UVR and other factors near the time of blood collection, the ability to explain 25(OH)D was modest.

Development and validation of a vitamin D status prediction model in Danish pregnant women: a study of the Danish National Birth Cohort

Vitamin D has been hypothesized to reduce risk of pregnancy complications such as preeclampsia, gestational diabetes mellitus, and preterm delivery. However, many of these outcomes are rare and require a large sample size to study, representing a challenge for cohorts with a limited number of preserved samples. The aims of this study were to (1) identify predictors of serum 25-hydroxy-vitamin D (25(OH)D) among pregnant women in a subsample (N = 1494) of the Danish National Birth Cohort (DNBC) and (2) develop and validate a score predicting 25(OH)D-status in order to explore associations between vitamin D and maternal and offspring health outcomes in the DNBC. In our study sample, 42.3% of the population had deficient levels of vitamin D (<50 nmol/L 25(OH)D) and average levels of 25(OH)D-status were 56.7(s.d. 24.6) nmol/L. A prediction model consisting of intake of vitamin D from diet and supplements, outdoor physical activity, tanning bed use, smoking, and month of blood draw explained 40.1% of the variance in 25(OH)D and mean measured 25(OH)D-level increased linearly by decile of predicted 25(OH)D-score. In total 32.2% of the women were placed in the same quintile by both measured and predicted 25(OH)D-values and 69.9% were placed in the same or adjacent quintile by both methods. Cohen's weighted kappa coefficient (Κ = 0.3) reflected fair agreement between measured 25(OH)D-levels and predicted 25(OH)D-score. These results are comparable to other settings in which vitamin D scores have shown similar associations with disease outcomes as measured 25(OH)D-levels. Our findings suggest that predicted 25(OH)D-scores may be a useful alternative to measured 25(OH)D for examining associations between vitamin D and disease outcomes in the DNBC cohort, but cannot substitute for measured 25(OH)D-levels for estimates of prevalence.

Solar ultraviolet-B radiation and vitamin D: a cross-sectional population-based study using data from the 2007 to 2009 Canadian Health Measures Survey

Background

Exposure to solar ultraviolet-B (UV-B) radiation is a major source of vitamin D3. Chemistry climate models project decreases in ground-level solar erythemal UV over the current century. It is unclear what impact this will have on vitamin D status at the population level. The purpose of this study was to measure the association between ground-level solar UV-B and serum concentrations of 25-hydroxyvitamin D (25(OH)D) using a secondary analysis of the 2007 to 2009 Canadian Health Measures Survey (CHMS).

Methods

Blood samples collected from individuals aged 12 to 79 years sampled across Canada were analyzed for 25(OH)D (n = 4,398). Solar UV-B irradiance was calculated for the 15 CHMS collection sites using the Tropospheric Ultraviolet and Visible Radiation Model. Multivariable linear regression was used to evaluate the association between 25(OH)D and solar UV-B adjusted for other predictors and to explore effect modification.

Results

Cumulative solar UV-B irradiance averaged over 91 days (91-day UV-B) prior to blood draw correlated significantly with 25(OH)D. Independent of other predictors, a 1 kJ/m² increase in 91-day UV-B was associated with a significant 0.5 nmol/L (95% CI 0.3-0.8) increase in mean 25(OH)D (P = 0.0001). The relationship was stronger among younger individuals and those spending more time outdoors. Based on current projections of decreases in ground-level solar UV-B, we predict less than a 1 nmol/L decrease in mean 25(OH)D for the population.

Conclusions

In Canada, cumulative exposure to ambient solar UV-B has a small but significant association with 25(OH)D concentrations. Public health messages to improve vitamin D status should target safe sun exposure with sunscreen use, and also enhanced dietary and supplemental intake and maintenance of a healthy body weight.

Risk factors for variation in 25-hydroxyvitamin D₃ and D₂ concentrations and vitamin D deficiency in children

CONTEXT

Vitamin D status is believed to be best indicated by serum 25-hydroxyvitamin D [25(OH)D; consisting of 25(OH)D₃ and 25(OH)D₂] that are obtained from different sources. Suboptimal vitamin D status is common and associated with adverse health outcomes.

OBJECTIVES

The objectives were to report the prevalence and risk factors of vitamin D deficiency and determine associations of characteristics that have been shown to relate to total 25(OH)D with 25(OH)D₃ and 25(OH)D₂ concentrations.

DESIGN AND SETTING

The Avon Longitudinal Study of Parents and Children is a population-based contemporary birth cohort (children born in 1991-1992) from southwest England.

PARTICIPANTS AND OUTCOME MEASURES

Seven thousand five hundred sixty children with serum 25(OH)D₃ and 25(OH)D₂ concentrations measured at the mean age of 9.9 yr participated in the study.

RESULTS

Vitamin D deficiency [total 25(OH)D concentration <20 ng/ml] was common (29%). The main risk factors were winter season, less time spent outdoors, low socioeconomic position, nonwhite ethnicity, older age, more advanced puberty stage, and female gender. Although there were some common risk factors for lower 25(OH)D₃ and 25(OH)D₂ concentrations (age, gender, puberty stage, body mass index, physical activity, household income, maternal education), several characteristics were associated with 25(OH)D₃ only (ethnicity, vitamin D intake, time spent outdoors, and UVB protection score) and others with 25(OH)D₂ only (protein and carbohydrate intake, parent's social class, and housing tenure).

CONCLUSIONS

Vitamin D deficiency was common in this contemporary U.K. cohort. Despite some overlap, there are differences in potential confounding structures for associations of 25(OH)D₃ and 25(OH)D₂ with health outcomes. These should be accounted for in future studies.

Vitamin d deficiency in postmenopausal breast cancer survivors

PURPOSE

Breast cancer survivors (BCS) taking aromatase inhibitors (AIs) are at an increased risk for decreased bone density and fractures. Given the role vitamin D plays in bone metabolism, we examined the prevalence of and risk factors for vitamin D deficiency in a study of postmenopausal BCS on AIs.

METHODS

We collected data on 391 postmenopausal women with stage I-III breast cancer on AI therapy. Vitamin D levels were measured by radioimmunoassay from patients' sera; deficiency was defined as a level < 30 ng/mL. Multivariate models were created to assess risk factors for deficiency.

RESULTS

The median vitamin D level was 35 ng/mL (range 6.78-93.15), and 35% of women were vitamin D deficient. When adjusting for age and vitamin D supplementation, minority participants were more likely to be vitamin D deficient than white women, (adjusted odds ratio [AOR] 2.18, 95% confidence interval [CI]1.22-3.89, p=0.009). Both overweight (AOR 3.05, 95% CI 1.72-5.41, p<0.001) and obese participants (AOR 3.21, 95% CI 1.79-5.78, p<0.001) had higher deficiency rates than did normal weight participants.

CONCLUSIONS

Hypovitaminosis D is common in BCS, and those who are nonwhite or overweight are at a higher risk of deficiency despite taking vitamin D supplements.

Predictors of 25-hydroxyvitamin D and its association with risk factors for prostate cancer: evidence from the prostate testing for cancer and treatment study

PURPOSE

Circulating 25-hydroxyvitamin D (25(OH)D) may protect against prostate and other cancers. Few epidemiology studies have measured 25(OH)D on all participants, weakening the evidence-base through reduced statistical power and the potential for bias. We developed a score to predict individual 25(OH)D based on potential predictors, including sun exposure, nutrient intake, and vitamin D pathway genes, providing a method of substituting missing values. We assessed the usefulness of predicted 25(OH)D by comparison with multiple imputation of 25(OH)D levels.

METHODS

Amongst 1,091 controls from a population-based case-control study (ProtecT), we quantified relationships of sun exposure, demographic, clinical, anthropologic, nutrient, and genetic data with circulating 25(OH)D and constructed several prediction scores from subsets of these measures. We investigated associations of three prostate cancer risk factors (PSA level, BMI, family history of prostate cancer) with 25(OH)D levels in sensitivity analyses based upon participants with measured 25(OH)D only and based upon the addition of all participants with missing 25(OH)D levels substituted by prediction score values or by multiple imputation.

RESULTS

Our score accounted for 27.7% of the variation in measured 25(OH)D. Associations with risk factors of prostate cancer were consistent across the different estimates of 25(OH)D. However, standard deviations for the prediction score did not incorporate extra error from prediction. Multiple imputation of missing 25(OH)D values predicted a more realistic range of 25(OH)D.

CONCLUSION

In epidemiological studies of cancer risk associated with vitamin D, multiple imputation of missing 25(OH)D is preferable to prediction scores, as a wider range of 25(OH)D levels are imputed and appropriate confidence intervals calculated.

Determinants of plasma 25-hydroxyvitamin D and development of prediction models in three US cohorts

Epidemiological and other evidence suggests that vitamin D may be protective against several chronic diseases. Assessing vitamin D status in epidemiological studies, however, is challenging given finite resources and limitations of commonly used approaches. Using multivariable linear regression, we derived predicted 25-hydroxyvitamin D (25(OH)D) scores based on known determinants of circulating 25(OH)D, including age, race, UV-B radiation flux at residence, dietary and supplementary vitamin D intakes, BMI, physical activity, alcohol intake, post-menopausal hormone use (women only) and season of blood draw, in three nationwide cohorts: the Nurses' Health Study, Nurses' Health Study II and the Health Professionals Follow-up Study. The model r 2 for each cohort ranged from 0·25 to 0·33. We validated the prediction models in independent samples of participants from these studies. Mean measured 25(OH)D levels rose with increasing decile of predicted 25(OH)D score, such that the differences in mean measured 25(OH)D between the extreme deciles of predicted 25(OH)D were in the range 8·7-12·3 ng/ml. Substituting predicted 25(OH)D scores for measured 25(OH)D in a previously published case-control analysis of colorectal cancer yielded similar effect estimates with OR of approximately 0·8 for a 10 ng/ml difference in either plasma or predicted 25(OH)D. We conclude that these data provide reasonable evidence that a predicted 25(OH)D score is an acceptable marker for ranking individuals by long-term vitamin D status and may be particularly useful in research settings where biomarkers are not available for the majority of a study population.

Common variation in vitamin D pathway genes predicts circulating 25-hydroxyvitamin D Levels among African Americans

Vitamin D is implicated in a wide range of health outcomes, and although environmental predictors of vitamin D levels are known, the genetic drivers of vitamin D status remain to be clarified. African Americans are a group at particularly high risk for vitamin D insufficiency but to date have been virtually absent from studies of genetic predictors of circulating vitamin D levels. Within the Southern Community Cohort Study, we investigated the association between 94 single nucleotide polymorphisms (SNPs) in five vitamin D pathway genes (GC, VDR, CYP2R1, CYP24A1, CYP27B1) and serum 25-hydroxyvitamin D (25(OH)D) levels among 379 African American and 379 Caucasian participants. We found statistically significant associations with three SNPs (rs2298849 and rs2282679 in the GC gene, and rs10877012 in the CYP27B1 gene), although only for African Americans. A genotype score, representing the number of risk alleles across the three SNPs, alone accounted for 4.6% of the variation in serum vitamin D among African Americans. A genotype score of 5 (vs. 1) was also associated with a 7.1 ng/mL reduction in serum 25(OH)D levels and a six-fold risk of vitamin D insufficiency (<20 ng/mL) (odds ratio 6.0, p = 0.01) among African Americans. With African ancestry determined from a panel of 276 ancestry informative SNPs, we found that high risk genotypes did not cluster among those with higher African ancestry. This study is one of the first to investigate common genetic variation in relation to vitamin D levels in African Americans, and the first to evaluate how vitamin D-associated genotypes vary in relation to African ancestry. These results suggest that further evaluation of genetic contributors to vitamin D status among African Americans may help provide insights regarding racial health disparities or enable the identification of subgroups especially in need of vitamin D-related interventions.

Vitamin D and racial disparity in albuminuria: NHANES 2001-2006

Background

National data show unexplained racial disparity in albuminuria. We assessed whether low serum vitamin D status contributes to racial disparity in albuminuria.

Methods

We examined the association between race and albuminuria (spot urinary albumin/creatinine ratio (ACR) ≥30) among non-Hispanic black and white nonpregnant adults who were free of renal impairment in the National Health and Nutrition Examination Survey (NHANES) from 2001–2006. We conducted analyses without and with serum 25(OH)D. We adjusted for age, sex, education level, smoking, body mass index (BMI), diabetes, diagnosis of hypertension, and use of antihypertensive medication.

Results

Albuminuria was present in 10.0% of non-Hispanic blacks and 6.6% in non-Hispanic whites. Being black (odds ratio (OR) 1.46; 95% confidence interval (CI) 1.23–1.73) was independently associated with albuminuria. There was a graded, inverse association between 25(OH)D level and albuminuria. Notably, the association between race and albuminuria was no longer significant (OR 1.19; 95% CI 0.97–1.47) after accounting for participants' serum 25(OH)D. Similar results were observed when participants with macroalbuminuria (ACR ≥300 mg/g) or elevated parathyroid hormone (>74 pg/ml) were excluded or when a continuous measure of 25(OH)D was substituted for the categorical measure. There were no interactions between race and vitamin D status though racial disparity in albuminuria was observed among participants with the highest 25(OH)D levels.

Conclusion

Suboptimal vitamin D status may contribute to racial disparity in albuminuria. Randomized controlled trials are needed to determine whether supplementation with vitamin analogues reduces risk for albuminuria or reduce racial disparity in this outcome.

A review of the health consequences of the vitamin D deficiency pandemic

Rickets, osteomalacia, osteoporosis and myopathy are among the better known consequences of a low to very low vitamin D status. Over the past several years various predominantly epidemiological and prospective cohort studies have found associations between low vitamin D levels and various extraskeletal conditions. These findings may particularly become important over the next years since large proportions of the population have low vitamin D levels. Increasing incidence rates of obesity, adverse life-style factors and active avoidance of sunlight seem to decrease average population mean vitamin D levels further. This article gives a brief overview of known and also less well-established potential detrimental effects of a low vitamin D status.

Elevated vitamin D status in postmenopausal women on thiazolidinediones for type 2 diabetes

Thiazolidenediones (TZD) have been reported to lead to non-vertebral bone loss in postmenopausal women with diabetes, but the true incidence of vertebral fractures has been under-detected because two-thirds of vertebral fractures are silent. TZD is also related to increased adiposity, with a consequently greater risk of vitamin D deficiency-both of which seem to aggravate the untoward effect of TZD on bone. The aim of this study is to determine whether TZD use is associated with prevalence of vertebral fractures and low vitamin D status in postmenopausal women with type 2 diabetes. A group of 102 postmenopausal women with type 2 diabetes, 52 TZD users for at least 12 months, and 50 non-TZD users were enrolled in the study. Any data regarding diabetes, age at menopause, co-morbidities, and drug use were recorded. Blood sampling and thoraco-lumbar radiography were performed. Bone mineral density (BMD) of L2-L4 and the femur were measured by dual-energy X-ray absorptiometry (DXA). The occurrence of vertebral fractures at one level or more in subjects on TZD was higher than those not on TZD, but did not reach statistical significance (19.2 vs. 14.0%, P = 0.5). Total hip BMD in subjects on TZD was significantly lower than those not on TZD (0.96 ± 0.15 vs. 1.02 ± 0.11; P < 0.05). Levels of 25(OH)D in TZD users were significantly higher (35.3 ± 1.5 vs. 25.9 ± 1.2 ng/dl; P < 0.001). The prevalence of vitamin D deficiency was 75.5% in subjects not on TZD compared to 34.6% in those on TZD (OR 6.4, 95% CI 2.6-15.6). Higher circulating 25(OH)D was observed in TZD users. TZD use was associated with lower total hip BMD but not with vertebral fracture.

Disease-specific definitions of vitamin D deficiency need to be established in autoimmune and non-autoimmune chronic diseases: a retrospective comparison of three chronic diseases

Introduction

We compared the odds of vitamin D deficiency in three chronic diseases: systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and type 2 diabetes (T2DM), adjusting for medications, demographics, and laboratory parameters, common to all three diseases. We also designed multivariate models to determine whether different factors are associated with vitamin D deficiency in different racial/ethnic groups.

Methods

We identified all patients with non-overlapping diagnoses of SLE, RA, and T2DM, with 25-hydroxyvitamin D (25OHD) levels measured between 2000 and 2009. Vitamin D deficiency was defined as 25OHD levels <20 ng/ml, based on previously established definitions. Race/ethnicity was analyzed as African-American non-Hispanic (African-American), Hispanic non-African-American (Hispanic), and Other based on self report.

Results

We included 3,914 patients in the final analysis: 123 SLE, 100 RA, and 3,691 T2DM. Among African-Americans the frequency of vitamin D deficiency was 59% in SLE, 47% in RA, and 67% in T2DM. Among Hispanics the frequency of vitamin D deficiency was 67% in SLE, 50% in RA, and 59% in T2DM. Compared with the SLE group, the adjusted odds ratio of vitamin D deficiency was 1.1, 95% CI (0.62, 2.1) in the RA group, and 2.0, 95% CI (1.3, 3.1) in the T2DM group. In the multivariate analysis, older age, higher serum calcium and bisphosphonate therapy were associated with a lower odds of vitamin D deficiency in all three racial/ethnic groups: 1,330 African-American, 1,257 Hispanic, and 1,100 Other. T2DM, serum creatinine, and vitamin D supplementation were associated with vitamin D deficiency in some, but not all, racial/ethnic groups.

Conclusions

Vitamin D deficiency is highly prevalent in our patients with SLE, RA, and T2DM. While the odds of vitamin D deficiency are similar in RA and SLE patients in a multivariate analysis, T2DM patients have much higher odds of being vitamin D deficient. Different demographic and laboratory factors may be associated with vitamin D deficiency within different racial/ethnic groups. Therefore, disease-specific and race/ethnicity-specific definitions of vitamin D deficiency need to be established in future studies in order to define goals of vitamin D replacement in patients with autoimmune and non-autoimmune chronic diseases.

Blood vitamin d levels in relation to genetic estimation of African ancestry

BACKGROUND

African-Americans generally have lower circulating levels of 25 hydroxyvitamin D [25(OH)D] than Whites, attributed to skin pigmentation and dietary habits. Little is known about the genetic determinants of 25(OH)D levels nor whether the degree of African ancestry associates with circulating 25(OH)D.

METHODS

With the use of a panel of 276 ancestry informative genetic markers, we estimated African and European admixture for a sample of 758 African-American and non-Hispanic White Southern Community Cohort Study participants. For African-Americans, cut points of <85%, 85% to 95%, and >or=95% defined low, medium, and high African ancestry, respectively. We estimated the association between African ancestry and 25(OH)D and also explored whether vitamin D exposure (sunlight, diet) had varying effects on 25(OH)D levels dependent on ancestry level.

RESULTS

The mean serum 25(OH)D levels among Whites and among African-Americans of low, medium, and high African ancestry were 27.2, 19.5, 18.3, and 16.5 ng/mL, respectively. Serum 25(OH)D was estimated to decrease by 1.0 to 1.1 ng/mL per 10% increase in African ancestry. The effect of high vitamin D exposure from sunlight and diet was 46% lower among African-Americans with high African ancestry than among those with low/medium ancestry.

CONCLUSIONS

We found novel evidence that the level of African ancestry may play a role in clinical vitamin D status.

IMPACT

This is the first study to describe how 25(OH)D levels vary in relation to genetic estimation of African ancestry. Further study is warranted to replicate these findings and uncover the potential pathways involved.