Effect of adiposity on vitamin D status and the 25-hydroxycholecalciferol response to supplementation in healthy young and older Irish adults

Vitamin D: determinants of status, indications for testing and knowledge in a convenience sample of Irish adults

Vitamin D deficiency is common in Irish adults, though there is limited research on its determinants, knowledge of vitamin D or indications for testing. We aimed to explore the determinants of vitamin D status in adults and examine knowledge and reasons for testing. The study population comprised adults who had serum 25-hydroxyvitamin D tested by general practitioners request at a Dublin Hospital in 2020. Questionnaires detailing dietary intake, sun exposure, ethnicity, biophysical factors and vitamin D knowledge were sent to a sample stratified by age, sex and vitamin D status. In total, there were 383 participants, mean age 56·0 (sd 16·6) years. Wintertime deficiency disproportionally affected non-white v. white (60 % v. 24 %, P < 0·001). The greatest predictors of deficiency were low vitamin D intake (< 10 μg/d) (P < 0·001) and non-white ethnicity (P = 0·006), followed by sun avoidance (P = 0·022). It was also more prevalent in those with lower body exposure when outdoors. The majority (86 %) identified vitamin D as important for bone health. However, 40 % were tested for non-clinical indications and half were not aware of the recommended daily allowance (RDA). Low vitamin D intake was the most important determinant of deficiency, but ethnicity and sun exposure habits were also significant predictors. The majority had no clear indication for testing and were not aware of the RDA. Public health policies to improve knowledge and vitamin D intake, especially for those of non-white ethnicity and with reduced sun exposure, should be considered.

Effects of Vitamin D Supplementation on Adipose Tissue Inflammation and NF-κB/AMPK Activation in Obese Mice Fed a High-Fat Diet

Adipose tissue expansion is strongly associated with increased adipose macrophage infiltration and adipocyte-derived pro-inflammatory cytokines, contributing to obesity-associated low-grade inflammation. Individuals with vitamin D deficiency have an increased prevalence of obesity and increased circulating inflammatory cytokines. However, the effect of vitamin D supplementation on obesity-induced inflammation remains controversial. Male C57BL/6J mice received a low-fat (10% fat) or high-fat (HF, 60% fat diet) containing 1000 IU vitamin D/kg diet, or HF supplemented with 10,000 IU vitamin D/kg diet for 16 weeks (n = 9/group). Vitamin D supplementation did not decrease HF-increased body weight but attenuated obesity-induced adipose hypertrophy and macrophage recruitment as demonstrated by the number of crown-like structures. Vitamin D supplementation significantly reduced the mRNA expression of CD11c, CD68, and iNOS, specific for inflammatory M1-like macrophages, and decreased serum levels of NO. In addition, significant reductions in pro-inflammatory gene expression of IL-6, MCP-1, and TNFα and mRNA levels of ASC-1, CASP1, and IL-1β involved in NLRP3 inflammasome were found in obese mice supplemented with vitamin D. Vitamin D supplementation significantly increased obesity-decreased AMPK activity and suppressed HF-increased NF-κB phosphorylation in adipose tissue from obese mice. These observed beneficial effects of vitamin D supplementation on adipose tissue expansion, macrophage recruitment, and inflammation might be related to AMPK/NF-κB signaling.

Necessity of daily 1000-IU vitamin D supplementation for maintaining a sufficient vitamin D status

The changes in the serum 25-hydroxyvitamin D (25(OH)D) concentrations after daily 1000-IU vitamin D intake for 3 months (3-month-VD), 6 months (6-month-VD) and then 6-month cessation of vitamin D in-take (6-month-VD cessation) were examined. The serum 25(OH)D levels in 11 male and 16 female subjects were 12.1±3.5 ng/mL at baseline, increased to 27.1±4.7 ng/mL at 3-month-VD, 28.5±5.1 ng/mL at 6-month-VD and decreased to 16.4±4.0 ng/mL at 6-month-VD cessation. The present study suggested that a vitamin D intake of 1000 IU/day is required to maintain the 25(OH) D concentration at 30 ng/mL or higher without vitamin D intoxication. J. Med. Invest. 69 : 135-140, February, 2022.

Tipping the Balance: Vitamin D Inadequacy in Children Impacts the Major Gut Bacterial Phyla

Vitamin D inadequacy appears to be on the rise globally, and it has been linked to an increased risk of osteoporosis, as well as metabolic, cardiovascular, and autoimmune diseases. Vitamin D concentrations are partially determined by genetic factors. Specific single nucleotide polymorphisms (SNPs) in genes involved in vitamin D transport, metabolism, or binding have been found to be associated with its serum concentration, and these SNPs differ among ethnicities. Vitamin D has also been suggested to be a regulator of the gut microbiota and vitamin D deficiency as the possible cause of gut microbial dysbiosis and inflammation. This pilot study aims to fill the gap in our understanding of the prevalence, cause, and implications of vitamin D inadequacy in a pediatric population residing in Qatar. Blood and fecal samples were collected from healthy subjects aged 4–14 years. Blood was used to measure serum metabolite of vitamin D, 25-hydroxycholecalciferol 25(OH)D. To evaluate the composition of the gut microbiota, fecal samples were subjected to 16S rRNA gene sequencing. High levels of vitamin D deficiency/insufficiency were observed in our cohort with 97% of the subjects falling into the inadequate category (with serum 25(OH)D < 75 nmol/L). The CT genotype in rs12512631, an SNP in the GC gene, was associated with low serum levels of vitamin D (ANOVA, p = 0.0356) and was abundant in deficient compared to non-deficient subjects. Overall gut microbial community structure was significantly different between the deficient (D) and non-deficient (ND) groups (Bray Curtis dissimilarity p = 0.049), with deficient subjects also displaying reduced gut microbial diversity. Significant differences were observed among the two major gut phyla, Firmicutes (F) and Bacteroidetes (B), where deficient subjects displayed a higher B/F ratio (p = 0.0097) compared to ND. Vitamin D deficient children also demonstrated gut enterotypes dominated by the genus Prevotella as opposed to Bacteroides. Our findings suggest that pediatric vitamin D inadequacy significantly impacts the gut microbiota. We also highlight the importance of considering host genetics and baseline gut microbiome composition in interpreting the clinical outcomes related to vitamin D deficiency as well as designing better personalized strategies for therapeutic interventions.

Vitamin D Status of the British African-Caribbean Residents: Analysis of the UK Biobank Cohort

The vitamin D status of the United Kingdom (UK) African-Caribbean (AC) population remains under-researched, despite an increased risk of vitamin D deficiency due to darker skin phenotypes and living at a high latitude. This cross-sectional study explored the vitamin D status and intake of AC individuals (n = 4046 with a valid serum 25(OH)D measurement) from the UK Biobank Cohort, aged ≥40 years at baseline (2006-2010). Over one third of the population were deficient (<25 nmol/L), 41.1% were insufficient (25-50 nmol/L) and 15.9% were sufficient (>50 nmol/L). Median (IQR) 25(OH)D was 30.0 (20.9) nmol/L. Logistic regression showed that brown/black skin phenotype, winter blood draw, not consuming oily fish and not using vitamin D supplements predicted increased odds of vitamin D deficiency, whilst older age and a summer or autumn blood draw were significantly associated with reduced odds of vitamin D deficiency. Vitamin D deficiency and insufficiency were prevalent in this AC population and is of considerable concern given the individual and societal implications of increased morbidity. Public health messaging for this group should focus on year-round vitamin D supplementation and increasing intakes of culturally appropriate vitamin D-rich foods. These data also support the urgent requirement for a revised vitamin D RNI for ethnic groups.

Serum 25-hydroxyvitamin D concentrations are inversely associated with body adiposity measurements but the association with bone mass is non-linear in postmenopausal women

Vitamin D deficiency has been linked to increased adiposity and decreased bone density. It is not known if vitamin D is linked to adiposity measures and bone mass in postmenopausal Qatar women. We investigated an association between serum vitamin D [25-hydroxyvitmain D (25(OH)D)] and adiposity measurements in postmenopausal women using Qatar Biobank data (n = 935). The post-menopausal status was self-reported by participants. Multivariate adjusted regression was applied to determine the association between serum 25(OH)D and body adiposity markers and bone mass. Serum 25(OH)D was significantly, inversely associated with body mass index (p < 0.0005), waist circumference (0.044), fat mass (p < 0.003), gynoid fat (p < 0.001), and android fat (p < 0.009). Serum 25(OH)D appeared to have an inverse 'U' association with several adiposity measures. Overall, body adiposity markers were the lowest in the 4^th quartile serum 25(OH)D and significantly lower compared to the 1^st quartile serum 25(OH)D. In multivariable adjusted analysis, no association was found between serum 25(OH)D concentration and bone mass when serum 25(OH)D was categorized. In a continuous variable analysis, the association between 25(OH)D and bone mass was significant, non-linear, inverse 'U'. In conclusion, serum 25-hydroxyvitamin D was inversely associated with adiposity measures and non-linearly associated to bone mass in postmenopausal Qatari women.

The supplementary effects of omega-3 fatty acid alone and in a combination with vitamin D3 on serum leptin levels: A randomized clinical trial on men and women with vitamin D deficiency

Purpose: This randomized clinical trial (RCT) was designed to assess the effect of VD3, n-3FA, and their combination on serum leptin levels in people with vitamin D deficiency (VDD).

Subjects and methods: One hundred and forty six participants, were randomly assigned into four groups supplemented with the dose of 50,000 IU VD3 taken weekly (D), 300 mg n-3FA taken daily (Om), and their combination (D+Om) or control (C) for eight weeks. Fasting baseline and follow-up (10 weeks; 8 weeks supplementation plus washout period of 2 weeks) of serum 25 hydroxyvitamin D (25OHD), leptin, glucose, triglycerides (TG), parathyroid hormone (PTH), calcium, and phosphorus were assayed. A paired T-test was used to assess the changes in serum leptin levels over of the follow-up period.

Results: Significant increase in follow-up serum leptin (10.62 ± 7.18 to 14.42 ± 8.29 ng/mL, P = 0.002) and TG (154 ± 84.4 to 200.1 ± 79, P = 0.015) levels were observed in n-3-FA supplemented group. Combination therapy (VD3 plus n-3 FA) significantly increased serum 25OHD (13.49 ± 4.64 to 37.09 ± 11.13 ng/mL, P &lt; 0.001), TG levels (114.3 ± 57.3 to 139.1 ± 60.7 mg/mL, P = 0.007) and insignificantly serum leptin (6.74 ± 4.87 to 8.01 ± 6.77 ng/mL, P = 0.269).

Conclusion: Our study referred that notable elevation in leptin and TG levels might be linked to leptin resistance. However, further RCTs are required to clarify possible consequences resulted from the extensive administration of n-3FA supplements and their combinations with high doses of VD3 supplements on humans’ health.

Associations of vitamin D with novel and traditional anthropometric indices according to age and sex: a cross-sectional study in central southern China

PURPOSE

Vitamin D insufficiency and obesity are recognized as worldwide concerns and have been linked with each other. New anthropometric indices reflect visceral obesity better than traditional anthropometric indices. Our aim was to identify the specific correlations of novel and traditional anthropometric indices with 25-hydroxyvitamin D (25(OH)D) concentrations by sex and age.

METHODS

Cross-sectional data on sociodemographic characteristics, lifestyle factors, clinical characteristics and biochemical measurements were collected for 12,617 Chinese adults. Four traditional anthropometric indices, body mass index (BMI), waist circumference (WC), waist-to-hip ratio (WHR) and waist-to-height ratio (WHtR), and two novel anthropometric indices, body roundness index (BRI) and body shape index (ABSI), were calculated.

RESULTS

In both sexes, the mean values of BMI, WC, WHtR and BRI tended to increase with 25(OH)D insufficiency, regardless of adjustment (all P < 0.05). Males with insufficient 25(OH)D had increased odds of obesity (assessed by BMI, WC, WHtR, BRI and ABSI) compared to the odds of males with sufficient 25(OH)D. Females with insufficient 25(OH)D had a higher chance of general obesity (assessed by BMI). Low 25(OH)D status was associated with indicators of obesity only in participants aged 45-64 years in both sexes.

CONCLUSION

A inverse association between obesity and lower vitamin D levels was found. Moreover, in addition to BMI, novel indicators of visceral adiposity, such as BRI and ABSI, were associated with lower 25(OH)D serum concentrations in males. The effects of optimizing vitamin D levels in obese Chinese adults need further examination, particularly in middle-aged males.

LEVEL OF EVIDENCE

Level V, cross-sectional descriptive study.

Interplay between Vitamin D, Obesity, and Other Metabolic Factors in a Multiethnic Adult Cohort

<b><i>Introduction:</i></b> Vitamin D deficiency and obesity have been classified as pandemic issues worldwide with high prevalence of both the risk factors in the United Arab Emirates. In recent years, obesity has been associated with vitamin D deficiency, but very few studies have been published about the correlation between them in the UAE population. <b><i>Subjects and Methods:</i></b> This is a cross-sectional study designed to find a correlation between vitamin D deficiency and obesity along with other metabolic factors. Data were collected from electronic medical records of 300 subjects ranging from 15 to 85 years of age of various ethnic origins residing in Dubai. <b><i>Results:</i></b> The study showed a high prevalence of obesity (44.9%) and vitamin D deficiency (40.1) in our study population. There is no evidence of a relation between vitamin D level and the obesity; 40.1% of the subjects were vitamin D deficient, out of which 46.7% were obese. However, a statistically significant relationship was found between cholesterol levels and vitamin D levels. Similarly, a significant relation was found between decreasing Vitamin D levels and increasing age but no relationship was detected with gender. <b><i>Conclusions:</i></b> The present study revealed an alarming prevalence of obesity and vitamin D deficiency. Further steps need to be taken to tackle this growing problem.

Effects of Vitamin D Supplementation on General and Central Obesity: Results from 20 Randomized Controlled Trials Involving Apparently Healthy Populations

Background: The obesity pandemic has been paralleled by a high prevalence of vitamin D deficiency (VDD). There is growing epidemiological evidence linking low vitamin D status with obesity events. In addition, observational studies also show that obesity may increase the risk of VDD. However, there is insufficient knowledge to understand whether there is a causality between the two. Moreover, the impact of vitamin D supplementation on obesity indices has shown inconsistent outcomes. Objective: This meta-analysis aimed to assess whether vitamin D supplementation modified general and central obesity indices in apparently healthy populations. Methods: A systematic retrieval of relevant randomized controlled trials (RCTs) was undertaken using Pubmed, Embase, Web of Knowledge and Chinese National Knowledge Infrastructure databases. The pooled weighted mean difference (WMD) and 95% confidence intervals (CI) were used to assess the changes in body mass index (BMI), waist circumference (WC), waist-to-hip ratio (WHR) and 25-hydroxyvitamin D (25[OH]D) from baseline. Results: Twenty RCTs involving 3,153 participants reporting either BMI, WC, WHR or 25(OH)D met the inclusion criteria. When compared with placebo, vitamin D supplementation had no significant decreases in BMI (WMD = –0.09 kg/m2, 95% CI –0.19 to 0.01, p = 0.08), WC (WMD = –0.71 cm, 95% CI –1.58 to 0.16, p = 0.112) or WHR (WMD = 0.00, 95% CI –0.01 to 0.01, p = 0.749). However, in the subgroups of females, Asia region studies and intervention duration ≥6 months, a beneficial and significant reduction in BMI and WC was noted (all p < 0.026). On the other hand, pooled results showed that there was a significant increase in serum 25(OH)D levels (WMD = 13.20 ng/mL, 95% CI 9.83–16.58, p < 0.001) after vitamin D intervention. No publication bias was found in our study. Conclusions: Overall, supplementation with vitamin D produced no significant effect on the BMI, WC or WHR of healthy adults.

Ultrasonographic measurements of the skin, fat and muscle in vitamin D deficiency

BACKGROUND

Vitamin D is a steroid hormone and it is essential for the musculoskeletal system health. The relationship among vitamin D levels and adiposity was shown. However, there is only one study seems to have examined the relationship between skinfold thickness and vitamin D levels.

METHODS

A total of 116 healthy subjects who had a recent vitamin D measurement were included. Skin, subcutaneous fat and muscle thicknesses were measured by ultrasound (US). Hand grip strength and usual gait speed were evaluated.

RESULTS

Subjects were classified into two groups according to 25-OH vitamin D levels. Skin thicknesses of anterior forearm in women and of anterior tibia in men, and trochanteric fat thicknesses of both genders were higher in lower 25-OH vitamin D group (both P < .05). There were no differences between the groups regarding muscle thicknesses, grip strength and gait speed (all P > .05). For identifying vitamin D deficiency (≤20 ng/mL); optimal skin thickness value was 1.25 mm in women (sensitivity: 91.3%, specificity: 54.7%), and optimal trochanteric fat thickness was 1.79 cm in men (sensitivity: 87.5%, specificity: 76.9). The specificity was increased to 79.2% if the cut-off value was taken as 1.35 mm for anterior forearm skin thickness in women.

CONCLUSION

We imply that skin thicknesses (anterior forearm and tibia) and subcutaneous fat (trochanteric region) increase in subjects with low vitamin D levels. Having also ascertained the relevant cut-off values, we underscore the possible role of these measurements as regards the assessment of vitamin D status.

Vitamin D levels in IBD: a randomised trial of weight-based versus fixed dose vitamin D supplementation

Objectives: Body weight is one of the factors affecting blood levels of 25-hydroxyvitamin D (25OHD). The aim of this study was to establish whether a vitamin D (vitD) weight-based dosing is more appropriate to a fixed daily dose in patients with inflammatory bowel disease (IBD).Materials/methods: This was an open label randomised trial. Patients with IBD were assigned to receive oral cholecalciferol at a dose of 28 IU/kg (IU/kg) or 2000 IU per day (IU/day) for 12 weeks during winter months. 25OHD plasma levels and other biochemical parameters were measured at baseline and after supplementation period. The primary outcome measure was 25OHD level after a follow-up period.Results: A total of 173 patients were analysed. The mean BMI was 25.5 ± 5.1 and initial mean 25OHD level was 62.7 ± 25.5 nmol/l. A similar increase (9.7 ± 26.9 vs 9.8 ± 26.7 nmol/l) in 25OHD levels occurred both in IU/kg and IU/day group. The proportion of subjects with normal and sub-normal levels following the substitution was comparable irrespective of body weight. The change in 25OHD level correlated positively only with the dose of vitD (p < .001) and negatively with the baseline 25OHD level (p < .001). A sustained 25OHD level of 75 nmol/l corresponds with a calculated daily vitD dose of 2034 IU.Conclusions: Weight-based dosing of vitamin D is not superior to a fixed dose in order to maintain stable 25OHD levels in IBD patients. Cholecalciferol dose of 2,000 IU/day is safe and sufficient during winter period.

Vitamin D and Cardio-Metabolic Risk Factors in Overweight Adults: An Overview of the Evidence

BACKGROUND

Several studies have suggested a potential association between low vitamin D serum levels and several pathological conditions apart from the well-known bone disorders. Thus, vitamin D insufficiency has been linked to cardiometabolic risk factors including obesity, insulin resistance, hypertension, dyslipidemia, as well as type 2 diabetes and cardiovascular disease.

OBJECTIVE

This review intends to provide an overview of recent evidence from clinical studies on vitamin D [25- hydroxyvitamin D (25(OH)D)] and cardiometabolic risk factors in overweight adults. Furthermore, we also discussed potential mechanisms and limits of the retrieved results.

METHODS

The search process was based on the selection of publications (RCT) listed in PubMed and Cochrane Library databases.

RESULTS

Vitamin D status evidenced an inversely strong association with subcutaneous adipose tissue and visceral adiposity, but not significantly related to other bodyweight measures (i.e., body mass index). Studies have shown a potential inverse association of hypovitaminosis D with insulin resistance and cardiovascular risk factors.

CONCLUSION

The mechanisms by which vitamin D deficiency enhances adiposity, as well as putative association with metabolic syndrome features, remain still unclear. Further investigation would be required to conclude whether vitamin D has an independent role in preventing cardiometabolic disorders.

A study of difference in serum 25-hydroxyvitamin D concentrations in patients with angiographically-defined coronary disease and healthy subjects

BACKGROUND

Cardiovascular disease (CVD) is one of the most important causes of death in developing countries. The current study evaluates the serum 25-hydroxyvitamin D (25OHD), phosphate and calcium levels in patients with angiographically-defined coronary artery disease (CAD) and healthy subjects in a sample population in northeastern Iran.

METHODS

There were 566 subjects aged between 20-80 years out of whom283 subjects with CAD were divided into two study groups based on their angiogram results; those with > 50% stenosis of one or more coronary arteries and those with ≤ 50% stenosis. Serum 25OHD levels and anthropometric parameters were measured for all subjects.

RESULTS

There were approximately 53% (n = 303) males and 47% (n = 269) females in the population sample. We found that crude serum 25OHD concentrations were significantly higher in both the Angio^- (21.6 ± 11.8 ng/ml) and Angio⁺ (21.3 ± 10.2 ng/ml) groups compared to the control subjects (16.4 ± 9.5 ng/ml) (P < 0.001).

CONCLUSION

The findings show that 25OHD state could be a risk factor for CAD, although this would need to be explored further, taking the potential confounding effects of diet into account in future studies.

Decreased Serum 25-Hydroxyvitamin D in Aging Male Mice Is Associated With Reduced Hepatic Cyp2r1 Abundance

The prevalence of vitamin D deficiency, as determined by circulating levels of 25-hydroxycalciferol [25(OH)D], is greater in older individuals compared with the young. To examine the hypothesis that altered production or inactivation of 25(OH)D contributes to lower circulating levels of 25(OH)D, we measured the serum levels of parent vitamin D3 (cholecalciferol) and 25(OH)D. We also determined the relative abundance of transcripts encoding hepatic CYP2R1 and CYP27B1, the principal 25-hydroxylases, transcripts encoding enzymes that degrade 25(OH)D in the liver (Cyp3A11) and kidney (Cyp24A1) and transcripts encoding megalin and cubilin, proteins critical to vitamin D resorption in the kidney in mice at three different ages. We observed a significant decline in the relative abundance of Cyp2R1 in the liver with aging (one-way ANOVA, P = 0.0077). Concurrent with the decrease in mRNA, a significant decline in hepatic CYP2R1 protein (one-way ANOVA for trend, P = 0.007) and 25(OH)D (one-way ANOVA for trend, P = 0.002) and in the ratio of 25(OH)D3 to cholecalciferol (one-way ANOVA, P = 0.0003). By contrast, levels of the transcripts encoding Cyp3a11, Cyp24a1, and Cyp27b1 megalin and cubilin were unchanged with aging. A significant positive correlation was found between Cyp2r1 mRNA and 25(OH)D, and a stronger correlation was found between Cyp2r1 mRNA and the ratio of 25(OH)D3 to cholecalciferol. These results indicate that decreased expression of CYP2R1 contributes to the reduced serum levels of 25(OH)D in aging.

Effect of Vitamin D Supplementation on Weight Loss, Glycemic Indices, and Lipid Profile in Obese and Overweight Women: A Clinical Trial Study

Introduction

Vitamin D (vit D) deficiency has defined as a health problem worldwide. World Health Organization (WHO) has declared that obesity is an epidemic of the 21^st century. Previous studies have shown that obesity may increase the risk of Vit D deficiency. Furthermore, other studies have demonstrated that vit D insufficiency was accompanied with higher risk of type 2 diabetes, cardiovascular diseases, hypertension, and obesity. The aim of this study was to survey the effect of vit D supplementation on weight loss among overweight and obese women aged 20-40 years in Isfahan.

Methods

This double-blind clinical trial was done on 50 overweight and obese women who were divided into two groups, in which one group received vit D supplements and the other group received placebo. Intervention group received vit D with dozes 50,000 IU/w for 6 weeks. The levels of total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-c), high-density lipoprotein cholesterol (HDL-c), fasting blood sugar (FBS), insulin (ins), homeostasis model assessment of ins resistance (IR), C-reactive protein (CRP), height, weight (WT), waist circumference (WC), hip circumference (HC), and blood pressure (BP) were measured before and after intervention.

Results

After using vit D supplementation for 6 weeks, WT, WC, and body mass index (BMI) were decreased significantly and serum vit D increased significantly compared to control group (P < 0.001). Other factors including TC, TG, LDL-c, HDL-c, FBS, CRP, ins, IR, and waist to hip ratio (WHR) did not change significantly (P > 0.05).

Conclusions

After 6 weeks of intervention, the means of WT, BMI, WC, and HC decreased significantly. Previous studies have shown that vit D deficiency was more prevalence in obese people and there was an inverse association among vit D with BMI and WC. The relationship between vit D and lipid profiles such as glycemic indexes, anthropometric indexes, CRP, and BP is not clear and needs more study in the future.

Fat Mass Is Associated with Serum 25-Hydroxyvitamin D Concentration Regardless of Body Size in Men

There are no large community-based studies examining the association of body size vs. body fat with vitamin D status. Association of serum 25-hydroxyvitamin D (25OHD) with body weight and subcategories of body weight defined by fat mass were evaluated in a large, free living population. Out of a total of 29,235 subjects from the 2008–2010 Korean National Health and Nutrition Examination Survey, the relevant data included 6458 subjects over 50 years of age who were analyzed cross-sectionally. Serum 25OHD concentrations were compared in men (n = 3164) and in women (n = 3294) by tertiles of body weight and body fat mass, as measured by Dual-energy X-ray Absorptiometry (DXA) within sex-specific tertiles of body weight. Serum 25OHD was weakly inversely correlated with body weight in the men and the women after adjustment for age (r = −0.075 and −0.073, respectively, p < 0.001 for both). Within each tertile of body weight, serum 25OHD decreased progressively as fat mass increased in men. This pattern was similar in the women but not consistently significant. Whereas body weight predicted a small decrease in serum 25OHD in the men and the women, greater adiposity, for any given weight, predicted larger decreases in the men, but not consistently in women.

Associations between 25-hydroxyvitamin D levels, body composition and metabolic profiles in young women

BACKGROUND/OBJECTIVES

Cardiovascular disease (CVD) is a major cause of mortality and morbidity globally. Results from previous studies are inconsistent and it remains unclear whether low-serum 25 OHD levels are associated with an increased risk of CVD. These associations have been little studied in young women. The aim of this study was to assess the relationship between serum 25 OHD and obesity, body composition, metabolic profiles and blood pressure in young women.

SUBJECTS/METHODS

Women aged 16-25 years living in Victoria, Australia, were recruited through Facebook advertising in this cross-sectional study. Participants completed an online survey and attended a site visit in a fasted state, where parameters, including blood pressure, anthropometry, metabolic profiles, serum 25 OHD levels and body composition (using dual energy X-ray absorptiometry) were measured.

RESULTS

A total of 557 participants were recruited into this study. Multiple linear regression analysis showed that after adjusting for visceral fat, season, smoking, physical activity, age, alcohol intake, oral contraceptive use, country of birth, taking multivitamins and taking vitamin D supplement, a 10 nmol/L increase in 25 OHD levels was associated with 0.65% greater HDL levels (p = 0.016) and 0.92% greater triglyceride levels (p = 0.003). It was also associated with 0.48% lower BMI (p < 0.001), 0.50% lower total fat percentage (p < 0.001), 0.09% lower visceral fat percentage (p < 0.001), 0.14% lower visceral fat to total fat ratio (p < 0.001) and 0.36% lower trunk fat to total fat ratio (p < 0.001), after adjustment for season, smoking, physical activity, age, alcohol intake, oral contraceptive use, country of birth, taking multivitamins and taking vitamin D supplements. Although these associations were statistically significant, they were very small in magnitude and of uncertain clinical significance.

CONCLUSIONS

These findings may help to explain an association between 25 OHD levels and CVD risk factors through associations with HDL, BMI, total body and visceral fat mass. Possible underlying mechanisms warrant further investigation.

The use of conjunctival ultraviolet autofluorescence (CUVAF) as a biomarker of time spent outdoors

PURPOSE

Conjunctival ultraviolet autofluorescence (CUVAF) has been used in previous Southern Hemisphere myopia research as a marker for time spent outdoors. The validity of CUVAF as an indicator of time spent outdoors is yet to be explored in the Northern Hemisphere. It is unclear if CUVAF represents damage attributed to UV exposure or dry eye. This cross-sectional study investigated the association between CUVAF measures, self-reported time spent outdoors and measures of dry eye.

METHODS

Participants were recruited from University staff and students (n = 50, 19-64 years; mean 41). None were using topical ocular medications (with the exception of dry eye treatments). Sun exposure and dry eye questionnaires (Ocular Surface Disease Index and McMonnies) were completed by the participant. Dryness was also assessed using slit lamp biomicroscopy and invasive tear break up time. Images of the temporal and nasal conjunctiva from the right and left eye were captured using a bespoke photography system. The total CUVAF area, average CUVAF pixel intensity per mm(2) and total CUVAF pixel intensity were analysed using MATLAB R2013a (The MathWorks Inc).

RESULTS

Of the 50 participants, 42% were classified as having dry eye. Self-reported sunglasses use was negatively associated with all CUVAF measures (Kruskal Wallis total CUVAF area, p = 0.04, ptrend  = 0.03, average CUVAF pixel intensity p = 0.02, ptrend  = 0.02, total CUVAF pixel intensity: p = 0.04, ptrend  = 0.02). Time spent outdoors was positively associated with all CUVAF measures (Spearman's correlation coefficients, total CUVAF area: r = 0.37, p = 0.01, average CUVAF pixel intensity: r = 0.36, p = 0.01, total CUVAF pixel intensity: r = 0.37, p = 0.01) and remained significant when sunglasses use was controlled for (partial correlation, total CUVAF area: r = 0.32, p = 0.03, average CUVAF pixel intensity: r = 0.39, p = 0.01, total CUVAF pixel intensity: r = 0.39, p = 0.03). Neither CUVAF area nor intensity measures were associated with any dry eye measure (Ocular Surface Disease Index: all p ≥ 0.41, corneal staining: all p ≥ 0.38, McMonnies: all r ≤ 0.09 all p ≥ 0.52, slit lamp biomicroscopy: all r ≤ 0.20 all p ≥ 0.17, invasive tear break up time: all r ≤ -0.07 all p ≥ 0.31).

CONCLUSIONS

CUVAF area and intensity were not associated with clinical measures of dry eye. Greater CUVAF area and intensity were associated with wearing sunglasses less frequently and spending more time outdoors. If sunglass wear is accounted for, CUVAF may be a useful biomarker of time spent outdoors in future myopia studies.

Vitamin D prohormone in the treatment of secondary hyperparathyroidism in patients with chronic kidney disease

Secondary hyperparathyroidism (sHPT) represents the adaptive and very often, finally, maladaptive response of the organism to control the disturbed homeostasis of calcium, phosphorus, and vitamin D metabolism caused by declining renal function in chronic kidney disease (CKD). sHPT leads to cardiovascular and extravascular calcifications and is directly linked to an increased risk of cardiovascular morbidity and mortality as well as excess all-cause mortality. Vitamin D plays an important role in the development of sHPT. CKD patients are characterized by a high prevalence of hypovitaminosis D. Supplementation with both vitamin D prohormones cholecalciferol and ergocalciferol enables the achievement and maintenance of a normal vitamin D status when given in adequate doses over an appropriate treatment period. In patients with earlier stages of CKD, sHPT is influenced by and can be successfully treated with vitamin D prohormone supplementation, whereas in patients with very late stages of CKD and those requiring dialysis, treatment with prohormones seems to be of limited efficacy. This review gives an overview of the pathogenesis of sHPT, summarizes vitamin D metabolism, and discusses the existing literature regarding the role of vitamin D prohormone in the treatment of sHPT in patients with CKD.

Vitamin D status and the prevalence of deficiency in lactating women from eight provinces and municipalities in China

BACKGROUND

Vitamin D deficiency has become prevalent worldwide in recent years. However, less evidence was available for lactating women.

OBJECTIVE

The purpose of the study was to understand vitamin D status and prevalence of deficiency in lactating women and associated risk factors for vitamin D deficiency from eight provinces and municipalities in China.

METHODS

Lactating women within 1-10 months postpartum were recruited in 2011-2013 from eight provinces and municipalities in China. Radioimmunoassay was used to measure serum 25-hydroxyvitamin D [25(OH)D] concentration. Standardized questionnaire was used to collect information on season, living site, ethnicity and socio-demographic characteristics.

RESULTS

Totally 2004 lactating women were recruited. The median (p25, p75) of 25(OH)D was 15.8 (10.5, 24.0) nmol/L. The prevalence of vitamin D deficiency was 85.3% as 25(OH)D <30nmol/L. Serum 25(OH)D levels of lactating women were significantly lower during October-January (14.0nmol/L) than during February-May (18.0nmol/L) (P<0.001), and were significantly higher in Dai ethnicity (22.5nmol/L) than in Hui ethnicity (Chinese Muslims) (9.0nmol/L) (P<0.001). For every 10,000 CNY annual income per capita increasing, serum 25(OH)D levels significantly increased 1.04 times (P<0.001). The odds of vitamin D deficiency in winter were 2.56 times higher than that in spring (OR 2.56, 95%CI: 1.91-3.43).

CONCLUSIONS

Vitamin D deficiency of lactating women was highly prevalent in the eight provinces and municipalities in China. It is urgent to study the strategy and intervention ways for improving vitamin D status of lactating women, especially for certain population groups during low sunlight exposure season.

A mouse model of vitamin D insufficiency: is there a relationship between 25(OH) vitamin D levels and obesity?

Background

Vitamin D insufficiency (serum 25-OH vitamin D > 10 ng/ml and < 30 ng/ml) is prevalent in the obese (body mass index (BMI) > 30 kg/m²), yet relationships between the two are poorly understood. Objectives of this study include identification of the impact of obesity on reducing serum 25-OH vitamin D concentration, particularly in response to altered vitamin D₃ supplementation, and to elucidate the longitudinal impact of serum 25-OH vitamin D on body mass index.

Methods

Twenty four-week-old lean and obese male C57BL/6 J mice were fed low, standard, or high levels of cholecalciferol supplementation and followed for 24 weeks. Longitudinal measurements include serum 25-OH and 1,25-(OH)₂ vitamin D, intact PTH, and calcium concentrations, as well as BMI, bone density and body fat/lean mass.

Results

Baseline serum 25-OH concentrations were not different in lean and obese mice (lean 32.8 ± 4.4 ng/ml versus obese 30.9 ± 1.6 ng/ml p = 0.09). Lean mice receiving low supplementation exhibited rapid declines in serum 25-OH vitamin D concentrations, falling from 33.4 ± 5.4 ng/ml to 14.5 ± 3.4 ng/ml after 2 weeks, while obese mice declined at a lower rate, falling from 30.9 ± 1.5 to 19.0 ± 0.9 ng/ml within the same time period. Surprisingly, high vitamin D₃ supplementation did not substantially increase serum vitamin D concentrations above standard supplementation, in either lean or obese mice. No differences in serum 1,25-(OH)₂ vitamin D, intact parathyroid hormone (PTH) or serum calcium were observed between lean and obese mice within the same vitamin D supplementation group. Yet obese mice exhibited lower serum calcitriol, higher serum PTH, and lower bone mineral density (BMD) than did lean mice. Additionally, neither body mass index nor body fat % was significantly correlated with vitamin D concentrations. Interestingly, lean mice with high vitamin D supplementation consumed significantly more food than did lean mice with standard or low supplementation (14.6 ± 1.7 kcal/mouse/day versus 11.8 ± 1.4 and 12.3 ± 1.7 respectively, p < 0.0001 for both).

Conclusions

Low cholecalciferol supplementation in both lean and obese mice significantly and sustainably reduces serum 25-OH vitamin D concentrations. Interestingly, obesity slowed the rate of decline. Over the period of the study, vitamin D insufficiency was not subsequently correlated with greater BMI/body fat, although lean mice with high supplementation consumed greater calories with no apparent BMI increase.

Lifestyle and Other Factors Explain One-Half of the Variability in the Serum 25-Hydroxyvitamin D Response to Cholecalciferol Supplementation in Healthy Adults

BACKGROUND

Many factors have been associated with serum 25-hydroxyvitamin D [25(OH)D] concentrations in observational studies, with variable consistency. However, less information is available on factors affecting the magnitude of changes in serum 25(OH)D resulting from vitamin D supplementation.

OBJECTIVE

This study aimed to identify factors associated with the serum 25(OH)D response to supplementation with 1000 IU cholecalciferol/d during the first year of a large, multicenter, randomized, placebo-controlled colorectal adenoma chemoprevention trial.

METHODS

Eligible older adults who were not vitamin D-deficient [serum 25(OH)D ≥12 ng/mL] were randomly assigned in a modified 2 × 2 factorial design to 1 of 4 groups: daily 1000 IU cholecalciferol, 1200 mg Ca as carbonate, both, or placebo. Women could elect 2-group (calcium ± cholecalciferol) random assignment. In secondary analyses, we used multivariable models to assess factors associated with serum 25(OH)D concentrations in all enrollees (n = 2753) and with relative changes in serum 25(OH)D after 1 y cholecalciferol supplementation among those randomly assigned (n = 2187).

RESULTS

In multivariable models, 8 factors accounted for 50% of the variability of proportional change in serum 25(OH)D after cholecalciferol supplementation. Larger increases were associated with being female (34.5% compared with 20.5%; P < 0.001) and with lower baseline serum 25(OH)D (P < 0.0001), optimal adherence to study pill intake (P = 0.0002), wearing long pants and sleeves during sun exposure (P = 0.0002), moderate activity level (P = 0.01), use of extra vitamin D-containing supplements during the trial (P = 0.03), and seasons of blood draw (P ≤ 0.002). Several genetic polymorphisms were associated with baseline serum 25(OH)D and/or serum response, but these did not substantially increase the models' R² values. Other factors, including body mass index, were associated with serum 25(OH)D at baseline but not with its response to supplemental cholecalciferol.

CONCLUSIONS

The factors that most affected changes in serum 25(OH)D concentrations in response to cholecalciferol supplementation included sex, baseline serum 25(OH)D, supplement intake adherence, skin-covering clothes, physical activity, and season. Genetic factors did not play a major role. This trial was registered at www.clinicaltrials.gov as NCT00153816.

Prediction of winter vitamin D status and requirements in the UK population based on 25(OH) vitamin D half-life and dietary intake data

On a population basis, there is a gradual decline in vitamin D status (plasma 25(OH)D) throughout winter. We developed a mathematical model to predict the population winter plasma 25(OH)D concentration longitudinally, using age-specific values for 25(OH)D expenditure (25(OH)D₃t_1/2), cross-sectional plasma 25(OH)D concentration and vitamin D intake (VDI) data from older (70+ years; n=492) and younger adults (18-69 years; n=448) participating in the UK National Diet and Nutrition Survey. From this model, the population VDI required to maintain the mean plasma 25(OH)D at a set concentration can be derived. As expected, both predicted and measured population 25(OH)D (mean (95%CI)) progressively declined from September to March (from 51 (40-61) to 38 (36-41)nmol/L (predicted) vs 38 (27-48)nmol/L (measured) in older people and from 59 (54-65) to 34 (31-37)nmol/L (predicted) vs 37 (31-44)nmol/L (measured) in younger people). The predicted and measured mean values closely matched. The predicted VDIs required to maintain mean winter plasma 25(OH)D at 50nmol/L at the population level were 10 (0-20) to 11 (9-14) and 11 (6-16) to 13(11-16)μg/d for older and younger adults, respectively dependent on the month. In conclusion, a prediction model accounting for 25(OH)D₃t_1/2, VDI and scaling factor for the 25(OH)D response to VDI, closely predicts measured population winter values. Refinements of this model may include specific scaling factors accounting for the 25(OH)D response at different VDIs and as influenced by body composition and specific values for 25(OH)D₃ t_1/2 dependent on host factors such as kidney function. This model may help to reduce the need for longitudinal measurements.

Serum 25-hydroxyvitamin D and insulin resistance in people at high risk of cardiovascular disease: a euglycaemic hyperinsulinaemic clamp study

CONTEXT

In observational studies, low serum 25-hydroxyvitamin D (25-OHD) concentration is associated with an increased risk of type 2 diabetes mellitus (DM). Increasing serum 25-OHD may have beneficial effects on insulin resistance or beta-cell function. Cross-sectional studies utilizing suboptimal methods for assessment of insulin sensitivity and serum 25-OHD concentration provide conflicting results.

OBJECTIVE

This study examined the relationship between serum 25-OHD concentration and insulin resistance in healthy overweight individuals at increased risk of cardiovascular disease, using optimal assessment techniques.

METHODS

A total of 92 subjects (mean age 56·0, SD 6·0 years), who were healthy but overweight (mean body mass index 30·9, SD 2·3 kg/m(2) ), underwent assessments of insulin sensitivity (two-step euglycaemic hyperinsulinaemic clamp, HOMA2-IR), beta-cell function (HOMA2%B), serum 25-OHD concentration and body composition (DEXA).

RESULTS

Mean total 25-OHD concentration was 32·2, range 21·8-46·6 nmol/l. No association was demonstrated between serum 25-OHD concentration and insulin resistance.

CONCLUSIONS

In this study using optimal assessment techniques to measure 25-OHD concentration, insulin sensitivity and body composition, there was no association between serum 25-OHD concentration and insulin resistance in healthy, overweight individuals at high risk of developing cardiovascular disease. This study suggests the documented inverse association between serum 25-OHD concentration and risk of type 2 DM is not mediated by a relationship between serum 25-OHD concentration and insulin resistance.

Vitamin D and insulin resistance

Vitamin D is a steroid hormone, which in active form binds to the vitamin D receptor. Expression of the vitamin D receptor in diverse cell types (pancreatic islet cells, myocytes, hepatocytes and adipocytes) raises the suspicion that vitamin D may be involved in multiple cellular processes, including the response to insulin. Insulin resistance is a characteristic feature of type 2 DM, and its attenuation may reduce the incidence of type 2 DM and cardiovascular disease. In observational studies, low serum 25-hydroxyvitamin D (25-OHD) concentrations are associated with an increased risk of type 2 DM. It has been suggested that increasing serum 25-OHD concentrations may have beneficial effects on glucose and insulin homeostasis. However, cross-sectional and interventional studies of vitamin D supplementation provide conflicting results and demonstrate no clear beneficial effect of vitamin D on insulin resistance. These studies are complicated by inclusion of different patient cohorts, different 25-OHD assays and different doses and preparations of vitamin D. Any possible association may be confounded by alterations in PTH, 1,25-dihydroxyvitamin D or tissue vitamin D concentrations. We identified 39 studies via MEDLINE and PUBMED. We review the evidence from 10 studies (seven observational and three interventional) examining vitamin D and type 2 DM incidence, and 29 studies (one prospective observational, 12 cross-sectional and 16 interventional trials) examining vitamin D and insulin resistance. Based on this data, it is not possible to state that vitamin D supplementation has any effect on type 2 DM incidence or on insulin resistance. Data from the multiple ongoing randomized controlled trials of vitamin D supplementation due to report over the next few years should help to clarify this area.

Prevalence and Correlates of Vitamin D Deficiency and Insufficiency in Luxembourg Adults: Evidence from the Observation of Cardiovascular Risk Factors (ORISCAV-LUX) Study

Evidence on vitamin D status and related risk factors in Luxembourg adults is lacking. This study aimed to determine the prevalence of vitamin D deficiency and insufficiency and related risk factors among healthy adults in Luxembourg. Based on clinicians’ observations, it was hypothesized that vitamin D deficiency and insufficiency might be common in our population, constituting a significant public health concern. A nationally representative random sample of 1432 adults was enrolled in the ORISCAV-LUX study, 2007–2008. The participants were divided into four categories according to their serum concentrations of 25-hydroxyvitamin D [25(OH)D]. Descriptive, univariate and multivariate statistical analyses used weighted methods to account for the stratified sampling scheme. Only 17.1% of the population had a “desirable” serum 25(OH)D level ≥75 nmol/L, whereas 27.1% had “inadequate” [serum 25(OH)D level 50–74 nmol/L], 40.4% had “insufficient” [serum 25(OH)D level 25–49 nmol/L], and 15.5% had “deficient” [serum 25(OH)D level <25 nmol/L)]. The prevalence of vitamin D deficiency was greater among current smokers, obese subjects, those having reduced HDL-cholesterol level and fair/poor self-perception of health, compared to their counterparts. The prevalence of vitamin D insufficiency was additionally higher among nondrinkers of alcohol, Portuguese and subjects from non-European countries. The final multivariate logistic regression analyses revealed that smoking status and obesity were independent correlates of vitamin D deficiency and insufficiency, respectively. Inadequate vitamin D status is highly prevalent among adults in Luxembourg and is associated with specific lifestyle factors. Along with the effect of vitamin D deficiency and insufficiency on the risk of several diseases, cancer and mortality, our findings have practical implications for public health dietary recommendations, and of particular importance for healthcare practitioners and policy makers.

Efficacy and safety of body weight-adapted oral cholecalciferol substitution in dialysis patients with vitamin D deficiency

Background

Vitamin D deficiency is highly prevalent in dialysis patients. Whether substitution of native vitamin D in these patients is beneficial is a matter of ongoing discussion, as is the optimal dosing schedule. The purpose of this study was to investigate the efficacy and safety of a body-weight adapted oral dosing regimen of cholecalciferol in dialysis patients.

Methods

In a prospective single-center study 56 prevalent dialysis patients with a baseline 25OHD₃ level <20 ng/mL received 100 IU of cholecalciferol per kg body weight once weekly orally for 26 weeks. 25OHD₃ was measured at baseline and at study end, iPTH every three months, serum calcium and phosphorous monthly. Concurrent medication including phosphate binders, calcitriol and cinacalcet and dialysate calcium concentration remained unchanged throughout the study.

Results

Baseline 25OHD₃ was 9.9 ± 4.1 ng/mL and increased to 26.1 ± 8.8 ng/mL (P = 0.01). Fourteen patients (27 %) achieved a level >30 ng/mL and all others above 20 ng/mL. Cinacalcet therapy was positively associated with the increase in 25OHD₃ (P = 0.024). The plasma iPTH level significantly decreased from median 362 pg/mL to 297 pg/mL (P = 0.01). This decline was more pronounced in patients with higher baseline iPTH levels (P < 0.01) and differed significantly dependent on concurrent calcitriol therapy. A significant iPTH decrease was observed in patients receiving calcitriol (P = 0.031). Serum calcium and phosphorous did not change significantly throughout the study period. Cholecalciferol substitution was well tolerated without adverse effects.

Conclusion

The dosing regimen of oral cholecalciferol supplementation with 100 IU per kg body weight per week for 26 weeks in dialysis patients with vitamin D deficiency causes a significant increase in 25OHD₃ close to the supposed target level of 30 ng/mL and a significant reduction in iPTH, without affecting serum calcium or phosphorous levels.

Effect of vitamin D supplementation alone or with calcium on adiposity measures: a systematic review and meta-analysis of randomized controlled trials

CONTEXT

The independent or interactive effects of vitamin D and calcium on adiposity remain inconclusive.

OBJECTIVE

The objective of this systematic review and meta-analysis was to assess whether vitamin D and calcium supplements cause changes in adiposity.

DATA SOURCES

MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials databases were searched for literature published from 1966 to March 2014.

STUDY SELECTION

A systematic search was conducted for randomized clinical trials with ≥ 50 participants aged ≥ 18 years at baseline who had received at least 12 weeks of treatment. Among the inclusion criteria were supplementation with vitamin D with or without calcium and measurement of adiposity (weight, body mass index [BMI], and/or fat mass).

DATA EXTRACTION

The primary endpoints assessed were changes in weight, BMI, or fat mass.

DATA SYNTHESIS

Of 953 trials identified, 26 randomized clinical trials (n = 12, vitamin D alone; n = 10, vitamin D plus calcium versus calcium control; n = 4, vitamin D plus calcium versus placebo) with a total of 42,430 participants (median duration, 12 months) met the inclusion criteria. When compared with placebo, vitamin D supplementation had no significant effect on BMI (weighted mean difference [WMD], -0.06 kg/m(2); 95% confidence interval [95%CI], -0.14 to 0.03), weight (WMD, -0.05 kg; 95%CI, -0.32 to 0.23), or fat mass (WMD, -0.43 kg; 95%CI, -1.69 to 0.84). Likewise, no significant reduction in BMI (WMD, 0.02 kg/m(2); 95%CI, -0.11 to 0.14), weight (WMD, 0.12 kg; 95%CI, -0.24 to 0.49), or fat mass (WMD, 0.12 kg; 95%CI, -0.22 to 0.45) was observed in participants who received vitamin D plus calcium compared with those who received calcium control.

CONCLUSIONS

Supplementation with vitamin D showed no effect on adiposity measures in adults.

Vitamin D and obesity: current perspectives and future directions

In recent years, new functional roles of vitamin D beyond its traditional role in calcium homoeostasis and bone metabolism have emerged linking the fat-soluble vitamin to various non-communicable diseases. Vitamin D deficiency (25-hydroxyvitamin D (25(OH)D) < 25-30 nmol/l) and sub-optimal status (25(OH)D < 50-100 nmol/l) are increasingly associated with unfavourable metabolic phenotypes, including insulin resistance, type 2 diabetes and CVD; conditions also commonly linked with overweight and obesity. Early studies reported poor vitamin D status in the morbidly obese. More recently, it has been observed that a graded relationship between vitamin D status and BMI, or specifically adiposity, exists in the general population. A number of hypotheses have been proposed to explain the potential mechanisms whereby alterations in the vitamin D endocrine system occur in the obese state. Plausible explanations include sequestration in adipose tissue, volumetric dilution or negative feedback mechanisms from increased circulating 1,25-dihydroxyvitamin D3. Others hypothesise that heavier individuals may partake in less outdoor activity, may also cover-up and wear more clothing than leaner individuals, thus decreasing sun exposure and limiting endogenous production of cholecalciferol in the skin. Moreover, in some but not all studies, BMI and adiposity have been negatively associated with the change in vitamin D status following vitamin D supplementation. It therefore remains unclear if body size and/or adiposity should be taken into account when determining the dietary requirements for vitamin D. This review will evaluate the current evidence linking vitamin D status and supplementation to overweight and obesity, and discuss the implications for setting dietary requirements.

Vitamin D and nifedipine in the treatment of Chinese patients with grades I-II essential hypertension: a randomized placebo-controlled trial

OBJECTIVES

Low vitamin D status has been shown to be associated with hypertension. We planned to research the effect of vitamin D and nifedipine in the treatment of patients with essential hypertension.

METHODS

Patients with grades I-II essential hypertension were enrolled in this single-center, double-blind, placebo-controlled trial in Beijing. All patients received a conventional antihypertensive drug (nifedipine, 30 mg/d). One hundred and twenty-six patients were randomly assigned to receive vitamin D (n=63, 2000 IU/d) or a placebo (n=63) as an add-on to nifedipine, by the method of permutated block randomization. Ambulatory blood pressure monitoring was performed at baseline (month 0), at month 3 and at month 6.

RESULTS

In vitamin D supplementation group, there was a significant increase in mean 25-hydroxyvitamin D levels from baseline (19.4 ± 11.6 ng/ml) to 6 months (34.1 ± 12.2 ng/ml; p<0.001). At 6 months, the primary end points, a difference in the fall of 24-h mean blood pressure, between the groups was -6.2 mmHg (95% CI -11.2; -1.1) for systolic blood pressure (p<0.001) and -4.2 mmHg (95% CI -8.8; -0.3) for diastolic blood pressure (p<0.001) under intention to treat analysis. In patients with vitamin D <30 ng/ml at baseline (n=113), 24-h mean blood pressure decreased by 7.1/5.7 mmHg (p<0.001). Safety and tolerability were similar among the two groups.

CONCLUSIONS

Vitamin D supplementation can reduce blood pressure in patients with hypertension, it can be an adjuvant therapy for patients with grades I-II essential hypertension.

CLINICAL TRIAL REGISTRATION

This study was registered in the Chinese Clinical Trial Registry, it is available in Website: http://www.chictr.org/cn/;

REGISTRATION NUMBER

ChiCTR-ONC-13003840.

Vitamin D: link between osteoporosis, obesity, and diabetes?

Vitamin D (1,25(OH)₂D₃) is a steroid hormone that has a range of physiological functions in skeletal and nonskeletal tissues, and can contribute to prevent and/or treat osteoporosis, obesity, and Type 2 diabetes mellitus (T2DM). In bone metabolism, vitamin D increases the plasma levels of calcium and phosphorus, regulates osteoblast and osteoclast the activity, and combats PTH hypersecretion, promoting bone formation and preventing/treating osteoporosis. This evidence is supported by most clinical studies, especially those that have included calcium and assessed the effects of vitamin D doses (≥800 IU/day) on bone mineral density. However, annual megadoses should be avoided as they impair bone health. Recent findings suggest that low serum vitamin D is the consequence (not the cause) of obesity and the results from randomized double-blind clinical trials are still scarce and inconclusive to establish the relationship between vitamin D, obesity, and T2DM. Nevertheless, there is evidence that vitamin D inhibits fat accumulation, increases insulin synthesis and preserves pancreatic islet cells, decreases insulin resistance and reduces hunger, favoring obesity and T2DM control. To date, there is not enough scientific evidence to support the use of vitamin D as a pathway to prevent and/or treat obesity and T2DM.

Vitamin D supplementation for prevention of mortality in adults

BACKGROUND

Available evidence on the effects of vitamin D on mortality has been inconclusive. In a recent systematic review, we found evidence that vitamin D3 may decrease mortality in mostly elderly women. The present systematic review updates and reassesses the benefits and harms of vitamin D supplementation used in primary and secondary prophylaxis of mortality.

OBJECTIVES

To assess the beneficial and harmful effects of vitamin D supplementation for prevention of mortality in healthy adults and adults in a stable phase of disease.

SEARCH METHODS

We searched The Cochrane Library, MEDLINE, EMBASE, LILACS, the Science Citation Index-Expanded and Conference Proceedings Citation Index-Science (all up to February 2012). We checked references of included trials and pharmaceutical companies for unidentified relevant trials.

SELECTION CRITERIA

Randomised trials that compared any type of vitamin D in any dose with any duration and route of administration versus placebo or no intervention in adult participants. Participants could have been recruited from the general population or from patients diagnosed with a disease in a stable phase. Vitamin D could have been administered as supplemental vitamin D (vitamin D3 (cholecalciferol) or vitamin D2 (ergocalciferol)) or as an active form of vitamin D (1α-hydroxyvitamin D (alfacalcidol) or 1,25-dihydroxyvitamin D (calcitriol)).

DATA COLLECTION AND ANALYSIS

Six review authors extracted data independently. Random-effects and fixed-effect meta-analyses were conducted. For dichotomous outcomes, we calculated the risk ratios (RRs). To account for trials with zero events, we performed meta-analyses of dichotomous data using risk differences (RDs) and empirical continuity corrections. We used published data and data obtained by contacting trial authors.To minimise the risk of systematic error, we assessed the risk of bias of the included trials. Trial sequential analyses controlled the risk of random errors possibly caused by cumulative meta-analyses.

MAIN RESULTS

We identified 159 randomised clinical trials. Ninety-four trials reported no mortality, and nine trials reported mortality but did not report in which intervention group the mortality occurred. Accordingly, 56 randomised trials with 95,286 participants provided usable data on mortality. The age of participants ranged from 18 to 107 years. Most trials included women older than 70 years. The mean proportion of women was 77%. Forty-eight of the trials randomly assigned 94,491 healthy participants. Of these, four trials included healthy volunteers, nine trials included postmenopausal women and 35 trials included older people living on their own or in institutional care. The remaining eight trials randomly assigned 795 participants with neurological, cardiovascular, respiratory or rheumatoid diseases. Vitamin D was administered for a weighted mean of 4.4 years. More than half of the trials had a low risk of bias. All trials were conducted in high-income countries. Forty-five trials (80%) reported the baseline vitamin D status of participants based on serum 25-hydroxyvitamin D levels. Participants in 19 trials had vitamin D adequacy (at or above 20 ng/mL). Participants in the remaining 26 trials had vitamin D insufficiency (less than 20 ng/mL).Vitamin D decreased mortality in all 56 trials analysed together (5,920/47,472 (12.5%) vs 6,077/47,814 (12.7%); RR 0.97 (95% confidence interval (CI) 0.94 to 0.99); P = 0.02; I(2) = 0%). More than 8% of participants dropped out. 'Worst-best case' and 'best-worst case' scenario analyses demonstrated that vitamin D could be associated with a dramatic increase or decrease in mortality. When different forms of vitamin D were assessed in separate analyses, only vitamin D3 decreased mortality (4,153/37,817 (11.0%) vs 4,340/38,110 (11.4%); RR 0.94 (95% CI 0.91 to 0.98); P = 0.002; I(2) = 0%; 75,927 participants; 38 trials). Vitamin D2, alfacalcidol and calcitriol did not significantly affect mortality. A subgroup analysis of trials at high risk of bias suggested that vitamin D2 may even increase mortality, but this finding could be due to random errors. Trial sequential analysis supported our finding regarding vitamin D3, with the cumulative Z-score breaking the trial sequential monitoring boundary for benefit, corresponding to 150 people treated over five years to prevent one additional death. We did not observe any statistically significant differences in the effect of vitamin D on mortality in subgroup analyses of trials at low risk of bias compared with trials at high risk of bias; of trials using placebo compared with trials using no intervention in the control group; of trials with no risk of industry bias compared with trials with risk of industry bias; of trials assessing primary prevention compared with trials assessing secondary prevention; of trials including participants with vitamin D level below 20 ng/mL at entry compared with trials including participants with vitamin D levels equal to or greater than 20 ng/mL at entry; of trials including ambulatory participants compared with trials including institutionalised participants; of trials using concomitant calcium supplementation compared with trials without calcium; of trials using a dose below 800 IU per day compared with trials using doses above 800 IU per day; and of trials including only women compared with trials including both sexes or only men. Vitamin D3 statistically significantly decreased cancer mortality (RR 0.88 (95% CI 0.78 to 0.98); P = 0.02; I(2) = 0%; 44,492 participants; 4 trials). Vitamin D3 combined with calcium increased the risk of nephrolithiasis (RR 1.17 (95% CI 1.02 to 1.34); P = 0.02; I(2) = 0%; 42,876 participants; 4 trials). Alfacalcidol and calcitriol increased the risk of hypercalcaemia (RR 3.18 (95% CI 1.17 to 8.68); P = 0.02; I(2) = 17%; 710 participants; 3 trials).

AUTHORS' CONCLUSIONS

Vitamin D3 seemed to decrease mortality in elderly people living independently or in institutional care. Vitamin D2, alfacalcidol and calcitriol had no statistically significant beneficial effects on mortality. Vitamin D3 combined with calcium increased nephrolithiasis. Both alfacalcidol and calcitriol increased hypercalcaemia. Because of risks of attrition bias originating from substantial dropout of participants and of outcome reporting bias due to a number of trials not reporting on mortality, as well as a number of other weaknesses in our evidence, further placebo-controlled randomised trials seem warranted.

A parallel group double-blind RCT of vitamin D3 assessing physical function: is the biochemical response to treatment affected by overweight and obesity?

Vitamin D may affect skeletal muscle function. In a double-blind, randomised, placebo-controlled trial, we found that vitamin D3 supplementation (400 or 1,000 I.U. vs. placebo daily for 1 year with bimonthly study visits) does not improve grip strength or reduce falls.

INTRODUCTION

This study aimed to test the supplementation effects of vitamin D3 on physical function and examine associations between overweight/obesity and the biochemical response to treatment.

METHODS

In a parallel group double-blind RCT, healthy postmenopausal women from North East Scotland (latitude-57° N) aged 60-70 years (body mass index (BMI), 18-45 kg/m(2)) were assigned (computer randomisation) to daily vitamin D3 (400 I.U. (n = 102)/1,000 I.U. (n = 101)) or matching placebo (n = 102) (97, 96 and 100 participants analysed for outcomes, respectively) from identical coded containers for 1 year. Grip strength (primary outcome), falls, diet, physical activity and ultraviolet B radiation exposure were measured bimonthly, as were serum 25(OH)D, adjusted calcium (ACa) and phosphate. Fat/lean mass (dual energy X-ray absorptiometry), anthropometry, 1,25-dihydroxyvitamin D and parathyroid hormone were measured at baseline and 12 months. Participants and researchers were blinded throughout intervention and analysis.

RESULTS

Treatment had no effect on grip strength (mean change (SD)/year = -0.5 (2.5), -0.9 (2.7) and -0.4 (3.3) kg force for 400/1,000 I.U. vitamin D3 and placebo groups, respectively (P = .10, ANOVA)) or falls (P = .65, chi-squared test). Biochemical responses were similar across BMI categories (<25.25-29.99, ≥30 kg/m(2)) with the exception of a small change at 12-months in serum ACa in overweight compared to non-overweight participants (P = .01, ANOVA; 1,000 I.U. group). In the placebo group, 25(OH)D peak concentration change (winter to summer) was negatively associated with weight (r = -.268), BMI (r = -.198), total (r = -.278) and trunk fat mass (r = -.251), with total and trunk fat mass predictive of winter to summer 25(OH)D change (P = .01/.004 respectively, linear regression).

CONCLUSION

We found no evidence of an improvement in physical function following vitamin D3 supplementation for 1 year.

Induction of STEAP4 correlates with 1,25-dihydroxyvitamin D3 stimulation of adipogenesis in mesenchymal progenitor cells derived from human adipose tissue

The vitamin D receptor (VDR) is expressed in human adipocytes and is transiently induced during early adipogenesis in mesenchymal progenitor cell models. VDR null mice exhibit enhanced energy expenditure and reduced adiposity even when fed high fat diets. Adipocyte-specific transgenic-expression of human VDR in mice enhances adipose tissue mass, indicating that VDR activation in adipocytes enhances lipid storage in vivo. In these studies, we conducted genomic profiling and differentiation assays in primary cultures of human adipose-derived mesenchymal progenitor cells to define the role of the VDR and its ligand 1,25-dihydroxyvitamin D3 (1,25D) in adipogenesis. In the presence of adipogenic media, 1,25D promoted lipid accumulation and enhanced the expression of FABP4, FASN, and PPARγ. Mesenchymal cells derived from 6-month old VDR null mice exhibited impaired adipogenesis ex vivo but differentiation was restored by stable expression of human VDR. STEAP4, a gene that encodes a metalloreductase linked to obesity, insulin sensitivity, metabolic homeostasis and inflammation, was highly induced in human adipose cells differentiated in the presence of 1,25D but was minimally affected by 1,25D in undifferentiated precursors. These studies provide a molecular basis for recent epidemiological associations between vitamin D status, body weight and insulin resistance which may have relevance for prevention or treatment of metabolic syndrome and obesity.

Vitamin D status predicts hand-grip strength in young adult women living in Auckland, New Zealand

The identification of the vitamin D receptor (VDR) in skeletal muscle tissue and research in muscle strength and development in VDR-null mice confirms a role for vitamin D in muscle function. The relationship between muscle strength and vitamin D status has been explored to some degree in older populations with regard to fall prevention, but there has been very little research in younger adults. This cross-sectional study considered the predictors of muscle strength in 137 young women (19-29 years) living in New Zealand. The following measurements were taken in the latter months of winter: plasma 25OHD, dominant (HGD) and non-dominant hand-grip (HGND) strength (hand-grip dynamometer), counter measure jump, and recreational physical activity (RPA) assessed from a recent physical activity questionnaire (RPAQ). Dietary intake was measured with a four-day food diary, and body composition using air displacement plethysmography. This was a relatively inactive group of women; total RPA ranged from 0 to 3.93h per week, mean (SD) 0.86(0.74) h, approximately 50% comprised outdoor activities. Mean 25OHD was 54(28)nmol/l, HGD and HGND were significantly different (t=6.049, p<0.001) at 27.3(5.8) and 25.6(5.7)kg respectively. Total RPA and 25OHD were entered into a linear regression model with handgrip strength as the dependent variable (Model R(2)=0.11, p=0.001 non-dominant, R(2)=0.13, p<0.001 dominant). Serum 25OHD was significantly associated with HGD (B(SE)=0.05(0.02), p=0.016) and HGND (B(SE)=0.04(0.02), p=0.019), independent of recreational physical activity. Recreational activity had an association with both hand-grip strength and serum 25OHD, and when each were adjusted to remove this association, 25OHD accounted for 4.3% of HGND and 4.5% of HGD. These results suggest that vitamin D status does have a small but significant association with hand-grip strength in this group of young women. Further investigation in this age group with a randomised controlled trial is justified. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Dietary vitamin D intake is not associated with 25-hydroxyvitamin D3 or parathyroid hormone in elderly subjects, whereas the calcium-to-phosphate ratio affects parathyroid hormone

This cross-sectional study investigates whether serum 25-hydroxyvitamin D3 [25(OH)D3] and intact parathyroid hormone (iPTH) are affected by vitamin D, calcium, or phosphate intake in 140 independently living elderly subjects from Germany (99 women and 41 men; age, 66-96 years). We hypothesized that habitual dietary intakes of vitamin D, calcium, and phosphate are not associated with 25(OH)D3 or iPTH and that body mass index confounds these associations. Serum 25(OH)D3 and iPTH were measured by an electrochemiluminescence immunoassay. Dietary intake was determined using a 3-day estimated dietary record. The median dietary intake levels of vitamin D, calcium, and phosphate were 3 μg/d, 999 mg/d, and 1250 mg/d, respectively. Multiple regression analyses confirmed that dietary vitamin D and calcium did not affect 25(OH)D3 or iPTH; however, supplemental intakes of vitamin D and calcium were associated with 25(OH)D3 after adjustment for age, sex, body composition, sun exposure, physical activity, and smoking. In addition, phosphate intake and the calcium-to-phosphate ratio were associated with iPTH after multiple adjustments. In a subgroup analysis, calcium and vitamin D supplements, as well as phosphate intake, were associated with 25(OH)D3 and/or iPTH in normal-weight subjects only. Our results indicate that habitual dietary vitamin D and calcium intakes have no independent effects on 25(OH)D3 or iPTH in elderly subjects without vitamin D deficiency, whereas phosphate intake and the calcium-to-phosphate ratio affect iPTH. However, vitamin D and calcium supplements may increase 25(OH)D3 and decrease iPTH, even during the summer, but the impact of supplements may depend on body mass index.

Serum 25-hydroxy vitamin D levels in relation to body mass index: a systematic review and meta-analysis

BACKGROUND

Although several cross-sectional studies have investigated serum vitamin D levels in relation to body mass index (BMI), findings are inconsistent.

OBJECTIVE

This systematic review and meta-analysis of published cross-sectional data was conducted to summarize the evidence on the link between serum vitamin D levels and BMI in adults.

METHODS

PubMed, ISI Web of Science, Scopus and Google scholar database were searched to May 2012 for all relevant published papers. We found 34 articles that reported the correlation coefficients between serum 25-hydroxy vitamin D (25(OH)D) levels and BMI in apparently healthy adults (>18 years). The primary analysis was done on these 34 papers that reported 37 correlation coefficients. To find the source of between-study heterogeneity, our secondary analysis was confined to eight studies that had used random sampling method and reported the correlations for the whole population.

RESULTS

Our meta-analysis on 34 relevant papers revealed an overall significant inverse, but weak, association between serum 25(OH)D levels and BMI (Fisher's Z = -0.15, 95% CI: -0.19, -0.11) with a significant heterogeneity between studies. In the subgroup analysis based on gender and study location (East vs. West), the inverse associations were significant in both genders (male: Fisher's Z = -0.11, 95% CI: -0.14, -0.08 and female: -0.14, 95% CI: -0.21, -0.08) and both study locations (East: -0.09, 95% CI: -0.14, -0.04 and West: -0.23, 95% CI: -0.31, -0.17). In the subgroup analysis based on developmental status of countries, the weak inverse association remained significant in developed countries (-0.17, 95% CI: -0.21, -0.14), but not in developing nations (-0.10, 95% CI: -0.20, 0.01). Using meta-regression, we found that latitude (P = 0.91) or longitude (P = 0.2) of cities did not significantly contribute to the computed effect sizes. When we restricted our analysis to eight selected studies that used random sampling method, we reached the same findings. In this analysis, gender and developmental status of countries explained the between-study heterogeneity.

CONCLUSION

There is a significant inverse weak correlation between serum 25(OH)D levels and BMI in adult population, except for women living in developing countries. Further research particularly in developing countries and populations living near the equator is needed.

The association between vitamin D and cardiometabolic risk factors in children: a systematic review

The objective of this systematic review was to evaluate the association between serum 25-hydroxyvitamin D (25OHD) and cardiometabolic risk in children and the effect of vitamin D supplementation on risk. We included 35 clinical trials, cross-sectional studies, case-control studies, and cohort studies that evaluated the relationship between 25OHD and blood pressure, lipid levels, insulin/glucose metabolism, endothelial dysfunction, and arterial stiffness. One randomized clinical trial that randomized adolescents to 2000 or 400 IU/d of vitamin D and found improvement in arterial stiffness in the high-dose group and worsening in the low-dose group. One cross-sectional study found no relationship between 25OHD and endothelial dysfunction. Of 12 cross-sectional studies, 10 found an inverse association between 25OHD and systolic blood pressure, although 2 trials found no relationship. There was no consistent association between 25OHD and lipid levels or insulin/glucose metabolism. Insufficient evidence was available to conclude that vitamin D supplementation yields cardiometabolic benefit.

25-Hydroxyvitamin D Supplementation and BMI Change: A Meta-Analysis of Randomized Controlled Trials

The impact of 25-hydroxyvitamin D (25[OH]D) supplementation on weight change remains controversial. The objective of this study was to summarize the effects of 25[OH]D supplementation (cholecalciferol or ergocalciferol) on BMI change through a meta-analysis of published clinical trials. We completed a systematic review of English articles, using MEDLINE (Ovid, Pubmed) from January 1, 1998 through January 1, 2013. The articles selected focused on 25[OH]D supplementation and body mass index (BMI) in randomized controlled trials (RCT’s). The association between 25[OH]D and mean BMI change was estimated utilizing a random effects model. A total of 30 studies were reviewed and 9 were included in the meta-analysis. Total participants included 1651 adults (82.6% women and mean age 47.9 years) and mean follow-up ranged between 6 to 196 weeks and mean daily 25[OH]D dose ranged from 200 IU to 1,110 IU. Five of the 9 studies included calcium supplementation in both groups. Average baseline BMI was 30.7 and 30.4 kg/m² in the intervention and control groups, respectively. Five studies suggested a beneficial effect for 25[OH]D supplementation for BMI change whereas 3 studies showed no effect of 25[OH]D supplementation on BMI change, and one showed a non-perceptible change. Meta-analysis of BMI values at end of trial showed no statistically significant difference in BMI change by use of 25[OH]D supplementation. Based on existing published trials, oral 25[OH]D supplementation does not significantly impact BMI change.