Levels of vitamin D and cardiometabolic disorders: systematic review and meta-analysis

Metabolic syndrome: A review of the role of vitamin D in mediating susceptibility and outcome

Despite the well-recognised role of vitamin D in a wide range of physiological processes, hypovitaminosis is common worldwide (prevalence 30%-50%) presumably arising from inadequate exposure to ultraviolet radiation and insufficient consumption. While generally not at the very low levels associated with rickets, hypovitaminosis D has been implicated in various very different, pathophysiological processes. These include putative effects on the pathogenesis of neoplastic change, inflammatory and demyelinating conditions, cardiovascular disease (CVD) and diabetes. This review focuses on the association between hypovitaminosis D and the metabolic syndrome as well as its component characteristics which are central obesity, glucose homeostasis, insulin resistance, hypertension and atherogenic dyslipidaemia. We also consider the effects of hypovitaminosis D on outcomes associated with the metabolic syndrome such as CVD, diabetes and non-alcoholic fatty liver disease. We structure this review into 3 distinct sections; the metabolic syndrome, vitamin D biochemistry and the putative association between hypovitaminosis D, the metabolic syndrome and cardiovascular risk.

Determinants of vitamin D supplement use in Canadians

OBJECTIVE

To determine the prevalence of vitamin D supplement use in Canadian adults and associations with demographic and socio-economic variables.

DESIGN

Data from the Healthy Aging module of the Canadian Community Health Survey were used to investigate the prevalence of vitamin D supplement use in Canadians aged 45 years and over. The prevalence of supplement use stratified by various behavioural and demographic characteristics was calculated and adjusted models were used to find associations with those factors.

SETTING

The ten provinces of Canada.

SUBJECTS

Canadians aged 45 years and over who participated in the Healthy Aging module of the Canadian Community Health Survey from 2008-2009.

RESULTS

The highest observed prevalence for women was 48·0 % in the 65-69 years age group and the highest prevalence for men was 25·3 % in the 70-74 years age group. Women had higher odds of vitamin D supplement use than men in all age groups. Not using supplements was more common in smokers, those who did not engage in leisure-time physical activities and who were either overweight or obese. Vitamin D supplement use increased with household income and level of education, and decreased with self-perceived health. Supplement use was higher in those with chronic conditions.

CONCLUSIONS

The inverse association with self-perceived health could be partly explained by age, chronic conditions and increased use of health-care services. Associations with higher income and education suggest a strong socio-economic influence and that individuals may not have the expendable income to purchase vitamin D supplements or knowledge of their health benefits.

Is the Association between Vitamin D and Cardiovascular Disease Risk Confounded by Obesity? Evidence from the Andhra Pradesh Children and Parents Study (APCAPS)

Background

Evidence of an association between serum vitamin D and cardiovascular disease risk is inconsistent and comes predominantly from studies in high-income settings. We assessed the association between serum levels of 25-hydroxyvitamin D₃ (25(OH)D) and cardiovascular disease risk factors in a population of young Indian adults.

Methods

Cross-sectional analyses of data from APCAPS (Andhra Pradesh Children and Parents Study); a prospective birth cohort study in rural south India. Participants were 1038 (40.3% females) adults aged 18-24 years. Main outcome measures were blood pressures, fasting serum lipids (cholesterols and triglycerides), fasting glucose, insulin, measures of arterial stiffness (aortic augmentation index and aortic pulse wave velocity (aPWV)), carotid intima-media thickness, body mass index (BMI) and body fat (dual X-ray absorptiometry).

Results

Vitamin D deficiency (≤20ng/ml) was observed in 41.1% of this lean (mean BMI: 19.5) and active (mean minutes of moderate or vigorous physical activity per day: 186) population. Vitamin D deficiency was associated with higher median body fat in both males (15.9% body fat in vitamin D deficient males vs. 14.6% in non-deficient males, p<0.05) and females (29.1% body fat in vitamin D deficient females vs. 27.8% in non-deficient females, p<0.05) but no associations were observed between vitamin D deficiency and mean BMI or median fat mass index (FMI). Except a weak inverse association with fasting insulin in males, there was no clear association between serum vitamin D levels and cardiovascular disease risk factors in fully adjusted models.

Conclusions

We did not find clear evidence for an association between serum vitamin D levels and cardiovascular disease risk factors. Our results, consistent with the limited evidence from randomised trials of vitamin D supplementation and Mendelian randomisation experiments, suggest that the postulated link between serum vitamin D and cardiovascular disease may be non-causal. Instead, it may be attributable to confounding by lifestyle factors such as obesity and physical inactivity which may provide more fruitful targets for cardiovascular disease prevention.

Obesity and vitamin D deficiency: a systematic review and meta-analysis

Over the past decade, there have been an increasing number of studies on the association between vitamin D deficiency and anthropometric state. However, we did not identify any meta-analyses of the relationship between obesity and vitamin D deficiency in different age groups. Thus, we evaluated the association between obesity and vitamin D deficiency. We searched for observational studies published up to April 2014 in PubMed/Medline, Web of Science and Scopus databases. We performed a meta-analysis in accordance with the random-effects model to obtain the summary measurement (prevalence ratio, PR). Among the 29,882 articles identified, 23 met the inclusion criteria. The prevalence of vitamin D deficiency was 35% higher in obese subjects compared to the eutrophic group (PR: 1.35; 95% CI: 1.21-1.50) and 24% higher than in the overweight group (PR: 1.24; 95% CI: 1.14-1.34). These results indicate that the prevalence of vitamin D deficiency was more elevated in obese subjects. The vitamin D deficiency was associated with obesity irrespective of age, latitude, cut-offs to define vitamin D deficiency and the Human Development Index of the study location.

Hypovitaminosis D and organ damage in patients with arterial hypertension: a multicenter double blind randomised controlled trial of cholecalciferol supplementation (HYPODD) : study design, clinical procedures and treatment protocol

INTRODUCTION

At this time, good quality randomized clinical trials assessing the effects of vitamin D supplementation on cardiometabolic outcomes are lacking in the international literature.

AIM

To fill this gap, the Working Group on Vitamin D and Cardiorenal Disorders established jointly by the Italian Society of Hypertension (SIIA) and the Forum in Bone and Mineral Research conceived the HYPODD study (HYPOvitaminosis D and organ Damage).

METHODS

HYPODD is a no-profit multicenter 12-month parallel-group double-blind placebo controlled randomized trial aiming to assess the effects of cholecalciferol supplementation on blood pressure control, antihypertensive drugs consumption and progression of target organ damage in patients with essential hypertension and 25-hydroxyvitamin D serum level lower than 20 ng/ml (vitamin D deficiency). HYPODD is coordinated by the European Society Excellence Center of Hypertension of Federico II University, Naples, and involves 12 academic institutions in Italy (Ancona, Milan, Padua, Perugia, Rome, Siena, Trieste, Turin, Udine, Varese, and Verona).

RESULTS AND CONCLUSION

The HYPODD study has been registered at the Agenzia Italiana del Farmaco-Osservatorio sulla Sperimentazione Clinica del Farmaco (AIFA-OsSC) and EUDRACT sites (n° 2012-003514-14) and has been approved by the Ethical Committees of all the Centers involved in the study. The patients' recruitment is currently underway.

Vitamin D status and metabolic syndrome in the elderly: the Rotterdam Study

OBJECTIVE

The effects of vitamin D in the elderly are inconsistent. The aim of this study was to evaluate the association between vitamin D status and the metabolic syndrome (MetS) in the elderly, as well as between vitamin D status and the components of MetS (i.e. serum glucose, triglycerides (TG), HDL cholesterol (HDL-C), waist circumference (WC), and blood pressure (BP)).

METHODS

The study was embedded in the Rotterdam Study, a population-based cohort of middle-aged and elderly adults. We analyzed data from 3240 people (median age 71.2 years) who did not have type 2 diabetes mellitus at baseline.

RESULTS

We found higher 25-hydroxyvitamin D (25(OH)D) concentrations associated with lower prevalence of MetS (odds ratio (OR); 95% CI: 0.61; 0.49, 0.77 for adequate levels (≥75  nmol/l) vs deficiency (<50  nmol/l). In addition, in analysis of the individual components, the ORs for adequate vs deficient vitamin D levels were: 0.66 (95% CI 0.53, 0.83) for elevated WC, 0.67 (95% CI 0.52, 0.86) for reduced HDL-C, 0.69 (95% CI 0.54, 0.88) for elevated TG, and 0.80 (95% CI 0.65, 0.99) for elevated fasting glucose. Vitamin D was not associated with elevated blood pressure, and ORs for adequacy vs deficiency were 0.82 (95% CI 0.65, 1.03).

CONCLUSION

Higher 25(OH)D concentrations in the elderly are associated with lower prevalence of MetS and, in particular, with more beneficial HDL-C, TG, WC, and serum glucose. Since the prevalence of vitamin D deficiency is common worldwide and its risk increases with age, if causality is proven, benefits of improving vitamin D status among the elderly may be great.

Relations of vitamin D status, gender and type 2 diabetes in middle-aged Caucasians

Vitamin D (Vit D) deficiency may be linked to the development of obesity-associated complications such as insulin resistance and type 2 diabetes. We therefore evaluated the relationship of Vit D serum concentrations with metabolic parameters and type 2 diabetes in middle-aged Caucasian men and women. One thousand six hundred and thirty-one Caucasians (832 males, 58.8 ± 9.7 years; 799 females, 59.7 ± 10.7 years) were evaluated in a cross-sectional study. Vit D status was assessed by measuring the serum concentration of 25-hydroxyvitamin D3 [25(OH)D3]. Type 2 diabetes prevalence was ascertained by medical history, fasting plasma glucose concentrations, oral glucose tolerance testing and/or glycosylated hemoglobin. Men displayed higher crude or seasonally adjusted 25(OH)D3 serum concentrations than women (24.64 ± 10.98 vs. 22.88 ± 11.6 ng/ml; P < 0.001). Strong associations between body mass index (BMI) and 25(OH)D3 were observed in both genders (P < 0.001). Seasonally adjusted levels of 25(OH)D3 revealed stronger associations with type 2 diabetes in women than men (P < 0.001). However, adjustment for BMI and other confounding variables revealed an independent inverse association of 25(OH)D3 with diabetes only in women (P < 0.001), whereas the association was abrogated in men. Using a 15 ng/ml 25(OH)D3 cutoff for binary comparison, adjusted odds ratios for having newly diagnosed or known type 2 diabetes more than doubled (2.95 [95 % CI 1.37-4.89] and 3.26 [1.59-6.68], respectively), in women below the cutoff. We conclude that in women, but not in men, low 25(OH)D3 serum levels are independently associated with type 2 diabetes. These findings suggest sex-specific effects of Vit D in the pathogenesis of type 2 diabetes.

Hypovitaminosis D in type 2 diabetes: relation with features of the metabolic syndrome and glycemic control

AIM

To assess the association of hypovitaminosis D with clinical and biochemical characteristics of type 2 diabetic patients and to determine the effect of glycemic control optimization on 25-hydroxyvitamin D (25(OH)D) concentrations.

METHODS

Cross-sectional study of 63 patients with type 2 diabetes (mean age 60 ± 9.8 years, 69.8% men). Twenty of the 63 patients were also studied before and after glycemic control optimization.

RESULTS

Mean 25(OH)D concentrations were 63.64 ± 25.51 nmol/L and 74.6% of patients had hypovitaminosis D. Compared with patients with vitamin D sufficiency, patients with hypovitaminosis D had higher prevalence of overweight or obesity (72.3% versus 37.5%; p = 0.012) and higher VLDL cholesterol (VLDL-c) (0.71 (0.24-3.59) versus 0.45 (0.13-1.6) mmol/L; p = 0.011) and C-reactive protein (3.28 (0.36-17.69) versus 1.87 (0.18-17.47) mg/L; p = 0.033) concentrations. The composition of HDL particles also differed in both groups, with higher relative content of triglycerides and lower of cholesterol in patients with hypovitaminosis D. After adjustment for age, seasonality and BMI, differences remained significant for VLDL-c and triglyceride content of HDL. No differences were found regarding other diabetes characteristics. Improvement of glycemic control (HbA1c 9.4 (7.6-14.8) versus 7.3 (6.2-8.7)%; p = 0.000) was accompanied by a decrease in 25(OH)D concentrations (72.7 ± 33.3 to 59.0 ± 21.0 nmol/L; p = 0.035). Correlation analysis revealed that changes in 25(OH)D concentrations were negatively associated to changes in HbA1c (r - 0.482; p = 0.032).

CONCLUSION

Hypovitaminosis D is associated with features of the metabolic syndrome in type 2 diabetes and improvement of glycemic control decreases 25(OH)D concentrations.

Nutrients other than carbohydrates: their effects on glucose homeostasis in humans

Besides carbohydrates, other nutrients, such as dietary protein and amino acids; the supply of fat, vitamin D, and vitamin K; and sodium intake seem to affect glucose homeostasis. Although their effect is less pronounced than that of the amount and composition of carbohydrates, it seems reasonable to consider how nutrient intake habits may be modified to support an improved glucose homeostasis. For instance, taking into account the effect of some nutrients to lower blood glucose concentration on a day-by-day basis might support improvement of glucose homeostasis in the long run. On the other hand, lowering sodium intake too much, as recommended to avoid the development of hypertension, particularly in sodium-sensitive people, might lead to insulin resistance and thereby might risk increasing fasting as well as postprandial blood glucose concentrations. This review summarizes the state of our knowledge of how several nutrients other than carbohydrates, such as protein, fatty acids, vitamin D, vitamin K, magnesium, zinc, chromium, and sodium, affect blood glucose concentrations. Sufficient evidence exists to show that, in prospective studies based on randomized controlled trials, these selected nutrients affect blood glucose regulation. The review describes potential mechanisms leading to the observed effect. As much as is possible from the available data, the extent of the effect, is considered.

The relationship between serum 25-hydroxyvitamin D concentration, cardiorespiratory fitness, and insulin resistance in Japanese men

Here, we aim to investigate the independent and combined associations of serum 25-hydroxyvitamin D (25(OH)D) and cardiorespiratory fitness (CRF) with glucose metabolism. Fasting blood samples of 107 men aged 40–79 years were analyzed for 25(OH)D, glucose, insulin, glycated hemoglobin, and lipid profile. Homeostasis model assessment of insulin resistance index (HOMA-IR) was calculated from the fasting concentrations of glucose and insulin. Visceral fat area (VFA) was determined by magnetic resonance imaging and CRF by measuring maximal oxygen uptake. Median 25(OH)D concentration was 36.3 nmol/L, while the prevalence of 25(OH)D deficiency was 74.8%. Participants with high CRF had significantly lower HOMA-IR, glycated hemoglobin, and insulin values than participants with low CRF (p < 0.05). Higher 25(OH)D concentration was strongly correlated with lower HOMA-IR and insulin values independent of VFA (p < 0.01) but significantly affected by CRF. In the high CRF group, participants with higher 25(OH)D concentration had lower HOMA-IR values than participants with low 25(OH)D concentration (p < 0.05). Higher 25(OH)D and CRF are crucial for reducing insulin resistance regardless of abdominal fat. In addition, higher 25(OH)D concentration may strengthen the effect of CRF on reducing insulin resistance in middle-aged and elderly Japanese men with high CRF.

The effect of vitamin D supplementation on serum lipids in postmenopausal women with diabetes: A randomized controlled trial

BACKGROUND & AIMS

Dyslipidemia is a risk factor for cardiovascular disease that has become an increasing public health problem. Dyslipidemia is especially relevant in vulnerable populations such as postmenopausal women. Low serum levels of 25-hydroxyvitamin D have been associated with an unfavourable lipid profile. Due to contradictory findings from intervention trials, we investigated the effect of vitamin D supplementation on serum lipids in postmenopausal women with type 2 diabetes.

METHODS

A total of 104 postmenopausal women with type 2 diabetes were randomly assigned in a double-blind manner to 1 of 2 groups taking a daily tablet for 6 months: a group consuming 4000 IU tablets of a vitamin D supplement (vitamin D group n = 52) or a group consuming placebo tablets (placebo group n = 52).

RESULTS

The study was completed by 99 participants. However, as the analysis was based on an intention-to-treat approach, all 104 women were included in the final analysis. In the vitamin D group mean serum levels of 25(OH)D3 improved significantly at the end of the follow-up period (+25.5 nmol/L; P = <0.001). Our findings revealed no significant changes in low density lipoproteins, high density lipoproteins and total cholesterol concentrations, but did identify a greater decrease in serum triglycerides in the vitamin D group. The average effect of supplementation on the treated group was -34.24 mg/dL (P = 0.021), while the average treatment effect was -31.8 mg/dL (P = 0.023).

CONCLUSIONS

Our results suggest that supplementation with vitamin D (4000 IU/d) may have a beneficial effect on serum triglyceride levels without otherwise affecting levels of other lipids.

TRIAL REGISTRATION

clinicaltrial.gov; identifier NCT01019642.

Does sufficient evidence exist to support a causal association between vitamin D status and cardiovascular disease risk? An assessment using Hill's criteria for causality

Serum 25-hydroxyvitamin D (25(OH)D) levels have been found to be inversely associated with both prevalent and incident cardiovascular disease (CVD) risk factors; dyslipidemia, hypertension and diabetes mellitus. This review looks for evidence of a causal association between low 25(OH)D levels and increased CVD risk. We evaluated journal articles in light of Hill's criteria for causality in a biological system. The results of our assessment are as follows. Strength of association: many randomized controlled trials (RCTs), prospective and cross-sectional studies found statistically significant inverse associations between 25(OH)D levels and CVD risk factors. Consistency of observed association: most studies found statistically significant inverse associations between 25(OH)D levels and CVD risk factors in various populations, locations and circumstances. Temporality of association: many RCTs and prospective studies found statistically significant inverse associations between 25(OH)D levels and CVD risk factors. Biological gradient (dose-response curve): most studies assessing 25(OH)D levels and CVD risk found an inverse association exhibiting a linear biological gradient. Plausibility of biology: several plausible cellular-level causative mechanisms and biological pathways may lead from a low 25(OH)D level to increased risk for CVD with mediators, such as dyslipidemia, hypertension and diabetes mellitus. Experimental evidence: some well-designed RCTs found increased CVD risk factors with decreasing 25(OH)D levels. Analogy: the association between serum 25(OH)D levels and CVD risk is analogous to that between 25(OH)D levels and the risk of overall cancer, periodontal disease, multiple sclerosis and breast cancer.

CONCLUSION

all relevant Hill criteria for a causal association in a biological system are satisfied to indicate a low 25(OH)D level as a CVD risk factor.

Effects of 12 weeks high dose vitamin D3 treatment on insulin sensitivity, beta cell function, and metabolic markers in patients with type 2 diabetes and vitamin D insufficiency - a double-blind, randomized, placebo-controlled trial

OBJECTIVES

Vitamin D insufficiency is common in subjects with type 2 diabetes. Observational studies suggest that vitamin D plays a role in the pathogenesis of type 2 diabetes. However, results of intervention studies have been inconsistent. We investigated the effects of improving vitamin D status on insulin sensitivity, insulin secretion, and inflammatory markers in patients with type 2 diabetes.

MATERIALS/METHODS

A double blind, randomized, placebo controlled trial was conducted. Sixteen patients with type 2 diabetes and hypovitaminosis D were recruited. Eight patients received colecalciferol and (280 μg daily for 2 weeks, 140 μg daily for 10 weeks) and 8 patients received identical placebo tablets for 12 weeks. Before and after intervention, patients underwent IVGTT, hyperinsulinemic euglycemic clamp, assessment of baseline high-frequency insulin pulsatility, glucose-entrained insulin pulsatility, DXA scans, 24-hour-ambulatory blood pressure monitorings, and fasting blood samples.

RESULTS

Serum-25(OH) vitamin D and serum-1,25(OH)₂ vitamin D increased significantly after 12 weeks in the intervention group (p=0.01, p=0.004). Serum-25(OH) vitamin D was also significantly higher in the vitamin D group compared to the placebo group (p=0.02) after intervention. Although no significant changes in insulin sensitivity, inflammation, blood pressure, lipid profile, or HbA1c were found, we observed borderline (p between 0.05 and 0.10) improvements of insulin secretion, in terms of c-peptide levels, first phase incremental AUC insulin and insulin secretory burst mass.

CONCLUSIONS

Improvement in vitamin D status does not improve insulin resistance, blood pressure, inflammation or HbA1c, but might increase insulin secretion in patients with established type 2 diabetes.

Low levels of 25-hydroxy vitamin D and active 1,25-dihydroxyvitamin D independently associated with type 2 diabetes mellitus in older Australian men: the Concord Health and Ageing in Men Project

OBJECTIVES

To examine the associations between serum 25-hydroxyvitamin D (25OHD) levels and the active vitamin D metabolite, 1,25-hydroxyvitamin D (1,25OHD), with type 2 diabetes mellitus (DM) in community-living men aged 70 and older.

DESIGN

Cross-sectional.

SETTING

A population-based, cross-sectional analysis of the baseline phase of the Concord Health and Ageing in Men Project (CHAMP), a large epidemiological study conducted in Sydney between January 2005 and May 2007.

PARTICIPANTS

Community dwelling men aged 70 and older taking part in CHAMP (N = 1,659).

MEASUREMENTS

Serum 25OHD and 1,25OHD levels, presence of DM, age, country of birth, season of blood collection, sun exposure, body mass index, vitamin D supplement use, statin use, income, measures of health, depression, activity of daily living disabilities, parathyroid hormone, estimated glomerular filtration rate, phosphate, and calcium.

RESULTS

The prevalence of DM was 20.0%. There was a significant association between low 25OHD and 1,25OHD levels and DM that remained after adjustment for a wide range of confounders and covariates of clinical significance such as comorbidity, renal function, calciotropic hormones, and medications.

CONCLUSION

25OHD and 1,25OHD levels were associated with DM. The independent association between serum 25OHD and 1,25OHD concentrations and DM raises the question of whether each of the two vitamin D metabolites may influence DM through different biological mechanisms and pathways.

National report on the association of serum vitamin D with cardiometabolic risk factors in the pediatric population of the Middle East and North Africa (MENA): the CASPIAN-III Study

OBJECTIVES

As the first, to our knowledge, nationwide study in the Middle East and North Africa (MENA), this study aimed to investigate the association of serum 25 hydroxy vitamin D [25(OH)D] levels with cardiometabolic risk factors in a nationally representative sample of the pediatric population in Iran. The second objective was to provide the prevalence of hypovitaminosis D and the percentiles of serum 25(OH)D in the study population.

METHODS

This national population-based study was conducted among 1100 Iranian students living in 27 provinces in Iran. The association of 25(OH)D with each cardiometabolic risk factor was determined after adjustment for age, gender, body mass index, and waist circumference.

RESULTS

Participants consisted of 1095 students (52% boys) with a mean age of 14.74 ± 2.61 y. The median 25(OH)D level corresponded to a vitamin D insufficiency level: 12.70 ng/mL in boys and 13.20 ng/mL in girls. Overall, 40% of participants were vitamin D deficient, and 39% had vitamin D insufficiency. There were no significant differences in these findings between boys and girls. Adjusted regression analysis revealed a significant weak inverse association of 25(OH)D with systolic blood pressure, diastolic blood pressure, total cholesterol, and low-density lipoprotein cholesterol. This association was significantly positive with high-density lipoprotein cholesterol, but not with fasting plasma glucose and metabolic syndrome.

CONCLUSION

We found a considerably high prevalence of hypovitaminosis D in the pediatric population of a sunny region. Our findings also revealed an association of hypovitaminosis D with many cardiometabolic risk factors from childhood; these associations were independent of obesity indexes. It is of special concern that the highly prevalent disorders of low 25(OH)D and low high-density lipoprotein cholesterol in children and adolescents of the MENA region had significant association. The clinical importance of our findings needs to be confirmed in longitudinal studies.

The trials and tribulations of vitamin D: time for the 'sunshine' vitamin to come in out of the cold - or just more broken promises?

We are presently faced with the competing notions of modern life being a 'state of vitamin D depletion', implying a widespread need to supplement with vitamin D, or, the opposite view, which is that the present evidence can only support at best selective targeted vitamin D intervention. This is important as there is evidence that over the last 40-50 years there were downwards global trends in serum 25(OH)D concentrations, while individual consumption of vitamin D as supplements rose. For this reason and many others, a large population-based interventional study, the VITAL trial, was designed to try to establish the health value of vitamin D supplementation. VITAL is a huge primary prevention trial looking at the effects of vitamin D repletion in preventing cancer and cardiovascular disease in a fundamentally healthy population. This may seem an unusual approach given that what we mostly know about vitamin D is that is has some effects on the skeleton. This review looks to explore current knowledge about vitamin D in health and disease, and at how this is now undergoing significant reappraisal and revision. We will carefully critique the VITAL study design to see if it will allow for the construction of the detailed portfolio of clinical evidence so urgently needed to allow us better to understand role of vitamin D supplementation in health and disease.

Vitamin D status and its determinants in children and adults among families in late summer in Denmark

The impact of the familial relationship on vitamin D status has not been investigated previously. The objective of the present cross-sectional study was to assess serum 25-hydroxyvitamin D (25(OH)D) concentration and its determinants in children and adults among families in late summer in Denmark (56°N). Data obtained from 755 apparently healthy children (4–17 years) and adults (18–60 years) recruited as families (n 200) in the VitmaD study were analysed. Blood samples were collected in September–October, and serum 25(OH)D concentration was measured by liquid chromatography–tandem MS. Information on potential determinants was obtained using questionnaires. The geometric mean serum 25(OH)D concentration was 72·1 (interquartile range 61·5–86·7) nmol/l (range 9–162 nmol/l), with 9 % of the subjects having 25(OH)D concentrations < 50 nmol/l. The intra-family correlation was 0·27 in all subjects, 0·24 in the adults and 0·42 in the children. Serum 25(OH)D concentration was negatively associated with BMI (P< 0·001) and positively associated with dietary vitamin D intake (P= 0·008), multivitamin use (P= 0·019), solarium use (P= 0·006), outdoor stay (P= 0·001), sun preference (P= 0·002) and sun vacation (P< 0·001), but was not associated with lifestyle-related factors in the adults when these were assessed together with the other determinants. In conclusion, the majority of children and adults among the families had serum 25(OH)D concentrations >50 nmol/l in late summer in Denmark. Both dietary and sun-related factors were determinants of vitamin D status and the familial component was stronger for the children than for the adults.

Vitamin D intakes of adults differ by income, gender and race/ethnicity in the U.S.A., 2007 to 2010

OBJECTIVE

To determine if dietary, supplemental and total vitamin D intakes in the USA are influenced by income, race/ethnicity or gender.

DESIGN

Cross-sectional. US vitamin D intakes were estimated by poverty income ratio (PIR), race/ethnicity and gender using 24 h dietary intake recalls and dietary supplement use questionnaires. Statistical analyses of weighted data were performed using SAS (version 9.2) to estimate means and their standard errors. Race and ethnic intake differences controlling for PIR, gender and age were assessed by ANCOVA.

SUBJECTS

Adults aged ≥19 years.

SETTING

The 2007-2010 National Health and Nutrition Examination Survey, USA.

RESULTS

Total (dietary and supplement) vitamin D intake was greater in the high (10.0 (se 0.30) μg/d) v. the medium (7.9 (se 0.3) μg/d) or the low (8.0 (se 0.3) μg/d) PIR categories. Total vitamin D intake of non-Hispanic Whites (10.6 (se 0.4) μg/d) was greater than that of Hispanics (8.1 (se 0.3) μg/d) and non-Hispanic Blacks (7.1 (se 0.3) μg/d). Supplemental vitamin D intake was greater by females (5.3 (se 0.2) μg/d) than by males (3.3 (se 0.2) μg/d). Participants with high income were more likely to be vitamin D supplement users (33.0%) than those with medium (22.5%) or low (17.6%) income. High-income non-Hispanic Whites had the lowest percentage (57%) not meeting the Estimated Average Requirement for vitamin D. Fortified milk and milk products provided 43.7% of the dietary vitamin D intake.

CONCLUSIONS

Public health efforts should expand the number of vitamin D-fortified foods and encourage the consumption of foods high in vitamin D and use of supplements.

Vitamin D and multiple health outcomes: umbrella review of systematic reviews and meta-analyses of observational studies and randomised trials

OBJECTIVE

To evaluate the breadth, validity, and presence of biases of the associations of vitamin D with diverse outcomes.

DESIGN

Umbrella review of the evidence across systematic reviews and meta-analyses of observational studies of plasma 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D concentrations and randomised controlled trials of vitamin D supplementation.

DATA SOURCES

Medline, Embase, and screening of citations and references.

ELIGIBILITY CRITERIA

Three types of studies were eligible for the umbrella review: systematic reviews and meta-analyses that examined observational associations between circulating vitamin D concentrations and any clinical outcome; and meta-analyses of randomised controlled trials assessing supplementation with vitamin D or active compounds (both established and newer compounds of vitamin D).

RESULTS

107 systematic literature reviews and 74 meta-analyses of observational studies of plasma vitamin D concentrations and 87 meta-analyses of randomised controlled trials of vitamin D supplementation were identified. The relation between vitamin D and 137 outcomes has been explored, covering a wide range of skeletal, malignant, cardiovascular, autoimmune, infectious, metabolic, and other diseases. Ten outcomes were examined by both meta-analyses of observational studies and meta-analyses of randomised controlled trials, but the direction of the effect and level of statistical significance was concordant only for birth weight (maternal vitamin D status or supplementation). On the basis of the available evidence, an association between vitamin D concentrations and birth weight, dental caries in children, maternal vitamin D concentrations at term, and parathyroid hormone concentrations in patients with chronic kidney disease requiring dialysis is probable, but further studies and better designed trials are needed to draw firmer conclusions. In contrast to previous reports, evidence does not support the argument that vitamin D only supplementation increases bone mineral density or reduces the risk of fractures or falls in older people.

CONCLUSIONS

Despite a few hundred systematic reviews and meta-analyses, highly convincing evidence of a clear role of vitamin D does not exist for any outcome, but associations with a selection of outcomes are probable.

Potential benefits of vitamin D supplementation in critically ill patients

AIM

To review potential benefits of vitamin D supplementation in critically ill patients.

METHODS

The data were collected by searching Scopus, PubMed/Medline, ScienceDirect, Clinical trials and Cochrane database systematic reviews. The keywords used as search terms were 'vitamin D', 'critically ill patients', 'ICU' and 'sepsis'.

RESULTS & CONCLUSION

Vitamin D deficiency is common in patients admitted to emergency departments, medical and surgical intensive care units. Positive effects of vitamin D on the immune system through decreasing inflammatory cytokines and increasing natural anti-infective molecules have been reported. Patients with low serum vitamin D concentrations experienced longer hospital stay and were more prone to nosocomial infections, including blood stream and respiratory infections. However, a correlation between vitamin D serum level and patients' mortality is not fully described. Limited studies have assessed effects of vitamin D supplementation on morbidity and mortality in critically ill patients. In the future, well-designed randomized clinical trials should describe the best dose, route and duration of vitamin D supplementation in critically ill patients.

Blood vitamin D status and metabolic syndrome in the general adult population: a dose-response meta-analysis

CONTEXT

Increasing evidence has suggested an association between blood vitamin D levels and metabolic syndrome.

OBJECTIVE

Our objective was to determine the relationship between blood vitamin D status and metabolic syndrome in the general adult population, using a dose-response meta-analysis.

DATA SOURCE

We searched the PubMed, EMBASE, Web of Science, and Cochrane Library databases through July 2013 to identify relevant studies.

STUDY SELECTION

Observational studies, reporting risk ratios with a 95% confidence interval (CI) for metabolic syndrome in ≥3 categories of blood 25-hydroxyvitamin D [25(OH)D] levels, were selected.

DATA EXTRACTION

Data extraction was performed independently by 2 authors, and the quality of the studies was evaluated using the risk of bias assessment tool for nonrandomized studies.

DATA SYNTHESIS

The pooled odds ratio of metabolic syndrome per 25 nmol/L increment in the serum/plasma 25(OH)D concentration was 0.87 (95% CI = 0.83-0.92, I(2) = 85%), based on 16 "cross-sectional studies" and 1.00 (95% CI = 0.98-1.02, I(2) = 0%) for 2 "cohort and nested case-control studies." The dose-response meta-analysis showed a generally linear, inverse relationship between 25(OH)D levels and metabolic syndrome in the cross-sectional studies (P for linear trend < .001).

CONCLUSIONS

Blood vitamin D levels were associated with a risk of metabolic syndrome in cross-sectional studies but not in longitudinal studies. Randomized, clinical trials will be necessary to address the issue of causality and to determine whether vitamin D supplementation is effective for the prevention of metabolic syndrome.

Vitamin D deficiency is associated with mortality and adverse vascular access outcomes in patients with end-stage renal disease

BACKGROUND

Plasma 25 hydroxycholecalciferol (vitamin D) deficiency has been associated with adverse cardiovascular outcomes in epidemiologic studies. Chronic kidney disease is associated with loss of 1α-hydroxylase and consequently vitamin D deficiency. We hypothesized that vitamin D deficiency was associated with increased mortality and increased vascular access failure in patients undergoing permanent vascular access for end-stage renal disease.

METHODS

This retrospective cohort study analyzed 128 patients undergoing permanent vascular access surgery between 2003 and 2012 for whom concurrent plasma vitamin D levels were also available. Levels were considered deficient at <20 ng/mL. Multivariable analysis was used to determine the association between vitamin D and mortality and vascular access outcomes.

RESULTS

The mean age was 66.7 years, 96.8% were male, 32.0% were African American, and 60.9% had diabetes mellitus. In the entire cohort, 55.5% were vitamin D-deficient, despite similar rates of repletion among the vitamin D-deficient and nondeficient groups. During a median follow-up of 2.73 years, there were 40 deaths (31%). Vitamin D-deficient patients tended to be younger (P = .01) and to have higher total cholesterol (P = .001) and lower albumin (P = .017) and calcium (P = .007) levels. Despite their younger age, mortality was significantly higher (P = .026) and vascular access failure was increased (P = .008) in the vitamin D-deficient group. Multivariate logistic regression analysis found vitamin D deficiency (odds ratio [OR], 3.64; 95% confidence interval [CI], 1.12-11.79; P = .031), hemodialysis through a central catheter (OR, 3.08; 95% CI, 1.04-9.12; P = .042), coronary artery disease (OR, 3.08; 95% CI, 1.06-8.94; P = .039), increased age (OR, 1.09; 95% CI, 1.03-1.15; P = .001), and albumin (OR, 0.27; 95% CI, 0.09-0.83; P = .023) remained independent predictors of mortality. Vitamin D deficiency (hazard ratio [HR], 2.34; 95% CI, 1.17-4.71; P = .02), a synthetic graft (HR, 3.50; 95% CI, 1.38-8.89; P = .009), and hyperlipidemia (HR, 0.42; 95% CI, 0.22-0.81; P = .01) were independent predictors of vascular access failure in a Cox proportional hazard model.

CONCLUSIONS

Vitamin D deficiency is highly prevalent in patients undergoing vascular access procedures. Patients who are deficient in vitamin D have worse survival and worse vascular access outcomes. Further study is warranted to assess whether aggressive vitamin D repletion will improve outcomes in this population.

Associations between serum 25-hydroxyvitamin D concentrations and multiple health conditions, physical performance measures, disability, and all-cause mortality: the Concord Health and Ageing in Men Project

OBJECTIVES

To explore associations between serum 25-hydroxyvitamin D (25(OH)D) levels and a wide range of health conditions, physical performance measures, disability, and mortality in a large epidemiological study to identify an optimum range for 25(OH)D concentrations.

DESIGN

Cross-sectional study, with additional prospective data on falls and mortality.

SETTING

Concord Health and Ageing in Men Project, Sydney, Australia.

PARTICIPANTS

Community-dwelling men aged 70 and older (N = 1,659).

MEASUREMENTS

Serum 25(OH)D levels, general health status, self-reported diseases, physical performance measures, disability (activities of daily living and instrumental activities of daily living) and falls.

RESULTS

Fair, poor, and very poor health; self-reported diabetes mellitus; hyperglycemia; depression; muscle weakness; poor balance; and all-cause mortality were all associated with serum 25(OH)D levels less than 50 nmol/L, even after adjustment for confounding. The findings also suggest that, in older men, for a wide range of health conditions, physical performance measures, disability, falls, and mortality, the optimum range of 25(OH)D is between 50.0 and 74.9 nmol/L, with no additional benefit for 25(OH)D levels of 75.0 nmol/L or greater.

CONCLUSION

Programs aimed at achieving an optimum range of serum 25(OH)D at levels between 50.0 and 74.9 nmol/L may have overall health benefits and such levels are adequate for older men.

Effects of a healthy Nordic diet on plasma 25-hydroxyvitamin D concentration in subjects with metabolic syndrome: a randomized, [corrected] controlled trial (SYSDIET)

PURPOSE

At northern latitudes, vitamin D is not synthesized endogenously during winter, causing low plasma 25-hydroxyvitamin D (25(OH)D) concentrations. Therefore, we evaluated the effects of a healthy Nordic diet based on Nordic nutrition recommendations (NNR) on plasma 25(OH)D and explored its dietary predictors.

METHODS

In a Nordic multi-centre trial, subjects (n = 213) with metabolic syndrome were randomized to a control or a healthy Nordic diet favouring fish (≥300 g/week, including ≥200 g/week fatty fish), whole-grain products, berries, fruits, vegetables, rapeseed oil and low-fat dairy products. Plasma 25(OH)D and parathyroid hormone were analysed before and after 18- to 24-week intervention.

RESULTS

At baseline, 45 % had vitamin D inadequacy (<50 nmol/l), whereas 8 % had deficiency (<25 nmol/l). Dietary vitamin D intake was increased by the healthy Nordic diet (P < 0.001). The healthy Nordic and the control diet reduced the prevalence of vitamin D inadequacy by 42 % (P < 0.001) and 19 % (P = 0.002), respectively, without between-group difference (P = 0.142). Compared with control, plasma 25(OH)D (P = 0.208) and parathyroid hormone (P = 0.207) were not altered by the healthy Nordic diet. Predictors for 25(OH)D were intake of vitamin D, eicosapentaenoic acids (EPA), docosahexaenoic acids (DHA), vitamin D supplement, plasma EPA and plasma DHA. Nevertheless, only vitamin D intake and season predicted the 25(OH)D changes.

CONCLUSION

Consuming a healthy Nordic diet based on NNR increased vitamin D intake but not plasma 25(OH)D concentration. The reason why fish consumption did not improve vitamin D status might be that many fish are farmed and might contain little vitamin D or that frying fish may result in vitamin D extraction. Additional ways to improve vitamin D status in Nordic countries may be needed.

Vitamin D intake and cardiometabolic risk factors in adolescents

BACKGROUND

A growing body of research suggests that vitamin D might play an important role in overall health. No data exist on vitamin D intake for the Azorean adolescent population. The purpose of this study was to assess vitamin D intake and investigate a possible association between vitamin D intake and cardiometabolic risk factors in Azorean adolescents.

METHODS

A cross-sectional school-based study was conducted on 496 adolescents (288 girls) aged 15-18 years from the Azorean Islands, Portugal. Anthropometric measurements (waist circumference and height), blood pressure (systolic), and plasma biomarkers [fasting glucose, insulin, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TGs)] were measured to assess metabolic risk. Homeostasis model assessment (HOMA), TC-to-HDL-C ratio, and waist-to-height ratio were calculated. For each of these variables, a Z-score was computed by age and sex. A metabolic risk score was constructed by summing the Z-scores of all individual risk factors. High risk was considered when the individual had ≥1 standard deviation (SD) of this score. Vitamin D intake was assessed with a semiquantitative food frequency questionnaire. Participants were classified into quartiles of vitamin D intake. Logistic regression was used to determine odds ratios for high cardiometabolic risk scores after adjusting for total energy intake, pubertal stage, fat mass percentage, and cardiorespiratory fitness.

RESULTS

Mean (SD) vitamin D intake was 5.8 (6.5) μg/day, and 9.1% of Azorean adolescents achieved the estimated average requirement of vitamin D (10 μg/day or 400 IU). Logistic regression showed that the odds ratio for a high cardiometabolic risk score was 3.35 [95% confidence interval (CI) 1.28-8.75] for adolescents in the lowest vitamin D intake quartile in comparison with those in the highest vitamin D intake quartile, even after adjustment for confounders.

CONCLUSION

A lower level of vitamin D intake was associated with worse metabolic profile among Azorean adolescents.

The role of the intraplaque vitamin d system in atherogenesis

Vitamin D has been shown to play critical activities in several physiological pathways not involving the calcium/phosphorus homeostasis. The ubiquitous distribution of the vitamin D receptor that is expressed in a variety of human and mouse tissues has strongly supported research on these "nonclassical" activities of vitamin D. On the other hand, the recent discovery of the expression also for vitamin D-related enzymes (such as 25-hydroxyvitamin D-1 α -hydroxylase and the catabolic enzyme 1,25-dihydroxyvitamin D-24-hydroxylase) in several tissues suggested that the vitamin D system is more complex than previously shown and it may act within tissues through autocrine and paracrine pathways. This updated model of vitamin D axis within peripheral tissues has been particularly investigated in atherosclerotic pathophysiology. This review aims at updating the role of the local vitamin D within atherosclerotic plaques, providing an overview of both intracellular mechanisms and cell-to-cell interactions. In addition, clinical findings about the potential causal relationship between vitamin D deficiency and atherogenesis will be analysed and discussed.

Does vitamin D sufficiency equate to a single serum 25-hydroxyvitamin D level or are different levels required for non-skeletal diseases?

Objective: Clarify the concept of vitamin D sufficiency, the relationship between efficacy and vitamin D status and the role of Vitamin D supplementation in the management of non-skeletal diseases. We outline reasons for anticipating different serum vitamin D levels are required for different diseases. Method: Review the literature for evidence of efficacy of supplementation and minimum effective 25-hydroxyvitamin D (25-OHD) levels in non-skeletal disease. Results: Evidence of efficacy of vitamin supplementation is graded according to levels of evidence. Minimum effective serum 25-OHD levels are lower for skeletal disease, e.g., rickets (25 nmol/L), osteoporosis and fractures (50 nmol/L), than for premature mortality (75 nmol/L) or non-skeletal diseases, e.g., depression (75 nmol/L), diabetes and cardiovascular disease (80 nmol/L), falls and respiratory infections (95 nmol/L) and cancer (100 nmol/L). Conclusions: Evidence for the efficacy of vitamin D supplementation at serum 25-OHD levels ranging from 25 to 100 nmol/L has been obtained from trials with vitamin D interventions that change vitamin D status by increasing serum 25-OHD to a level consistent with sufficiency for that disease. This evidence supports the hypothesis that just as vitamin D metabolism is tissue dependent, so the serum levels of 25-OHD signifying deficiency or sufficiency are disease dependent.

Vitamin D deficiency in alcohol-use disorders and its relationship to comorbid major depression: a cross-sectional study of inpatients in Nepal

BACKGROUND

Mounting evidence suggests that deficiency of vitamin D may be associated with major health problems, including alcohol-use disorders (AUD) and major depression (MD). This study aimed to identify the vitamin D status of Nepalese inpatients with an AUD. We explored socio-demographic and alcohol-use related correlates and the relationship between vitamin D deficiency and comorbid MD.

METHODS

A cross-sectional study was conducted on AUD inpatients (N=174) at eight alcohol/drug treatment centres around Kathmandu. Structured questionnaires were administered to assess the socio-demographic and alcohol-use parameters and to establish DSM-IV diagnoses of AUD and MD. Vitamin D deficiency was defined as a serum 25-hydroxyvitamin D (25(OH)D) concentration of <50 nmol/L.

RESULTS

The prevalence of vitamin D deficiency was 64%. Higher age, having a stable job or business, shorter time since last alcohol intake and winter serum samples were related to having lower 25(OH)D levels. Several features of AUD severity were associated with low vitamin D levels: guilt about drinking, using alcohol as eye-opener, and history of relapse after alcohol treatment (p ≤ 0.03). Patients with a comorbid major depression, in particular secondarily depressed cases, were less likely to have vitamin D deficiency (X(2)=6.8; p=0.01).

CONCLUSIONS

This study confirms high rates of vitamin D deficiency in alcohol treatment sample and shows a positive association between vitamin D deficiency and severity of alcohol-use disorders. Competing risk and other confounders may help explain the vitamin D status among patients with alcohol-use disorders and comorbid major depression.

Effect of diet on vascular health

Cardiovascular disease (CVD) is a major cause of morbidity and mortality in the Western world in older people. Diet and lifestyle change can reduce CVD risk in older people, and this evidence base is reviewed. For example, diets low in trans fats can reduce CVD risk, while for saturated fats the CVD-lowering effect depends on what is substituted for the saturated fat. Diets rich in fish reduce CVD risk, although n-3 supplements have not been shown to have a consistent effect on CVD end-points. Antioxidant and B-group vitamin supplementation are unlikely to reduce CVD risk, but diets rich in these micronutrients (e.g. rich in fruits and vegetables and the Mediterranean diet) are associated with lower CVD risk, while, for the Mediterranean diet, this has been supported by randomized controlled trials. Maintaining a healthy weight and being physically active reduce CVD risk factors and CVD incidence and mortality.

The relationship between vitamin D status and HIV-related complications in HIV-infected children and young adults

BACKGROUND

In HIV-infected adults, we and others have shown that vitamin D deficiency is independently associated with increased carotid intima-media thickness (cIMT), a surrogate marker for cardiovascular disease (CVD). This study explored for the first time the relationship between vitamin D and CVD risk in HIV-infected youth.

METHODS

This is a cross-sectional assessment of cIMT, inflammation, metabolic markers and vitamin D status in HIV-infected youth and healthy controls. We measured serum 25-hydroxyvitamin D (25(OH)D), fasting lipids, insulin, glucose, inflammatory markers and cIMT.

RESULTS

Thirty HIV-infected subjects and 31 controls were included. Among HIV-infected subjects, median age was 11 years (37% males; 73% black; similar to controls). HIV-infected subjects' mean (standard deviation) serum 25(OH)D was 24 (35) ng/mL; 70% had 25(OH)D<20 ng/mL (deficient), 23% between 20-30 ng/mL (insufficient) and 7%>30 ng/mL (sufficient); proportions were similar to controls (P=0.17). After adjusting for season, sex and race, there was no difference in serum 25(OH)D between groups (P=0.11). Serum 25(OH)D was not significantly correlated with cIMT, inflammatory markers or lipids. Serum 25(OH)D was negatively correlated with body mass index, insulin resistance, HIV duration, and cumulative use of antiretroviral therapy, non- and nucleoside reverse transcriptase inhibitors.

CONCLUSIONS

Most HIV-infected youth have vitamin D deficiency or insufficiency. Despite no direct association between serum 25(OH)D and cIMT, there were notable associations with some CVD risk factors, particularly inverse correlation with insulin resistance. Studies are needed to determine whether CVD risk, including insulin resistance, could be improved with vitamin D supplementation.

Vitamin D - a systematic literature review for the 5th edition of the Nordic Nutrition Recommendations

BACKGROUND

The present literature review is part of the NNR5 project with the aim of reviewing and updating the scientific basis of the 4th edition of the Nordic Nutrition Recommendations (NNR) issued in 2004.

OBJECTIVES

The overall aim was to review recent scientific data on the requirements and health effects of vitamin D and to report it to the NNR5 Working Group, who is responsible for updating the current dietary reference values valid in the Nordic countries.

METHODS

The electronic databases MEDLINE and Swemed were searched. We formulated eight questions which were used for the search. The search terms related to vitamin D status and intake and different health outcomes as well as to the effect of different vitamin D sources on vitamin D status. The search was done in two batches, the first covering January 2000-March 2010 and the second March 2009-February 2011. In the first search, we focused only on systematic literature reviews (SLRs) and in the second on SLRs and randomized control trials (RCTs) published after March 2009. Furthermore, we used snowballing for SLRs and IRCTs published between February 2011 and May 2012. The abstracts as well as the selected full-text papers were evaluated in pairs.

RESULTS

We found 1,706 studies in the two searches of which 28 studies were included in our review. We found 7 more by snowballing, thus 35 papers were included in total. Of these studies, 31 were SLRs and 4 were RCTs. The SLRs were generally of good or fair quality, whereas that of the included studies varied from good to poor. The heterogeneity of the studies included in the SLRs was large which made it difficult to interpret the results and provide single summary statements. One factor increasing the heterogeneity is the large variation in the assays used for assessing 25-hydroxyvitamin D concentration [25(OH)D], the marker of vitamin D status. The SLRs we have reviewed conclude that the evidence for a protective effect of vitamin D is only conclusive concerning bone health, total mortality and the risk of falling. Moreover, the effect was often only seen in persons with low basal 25(OH)D concentrations. In addition, most intervention studies leading to these conclusions report that intervention with vitamin D combined with calcium and not vitamin D alone gives these benefits. It was difficult to establish an optimal 25(OH)D concentration or vitamin D intake based on the SLRs, but there are evidence that a concentration of ≥50 nmol/l could be optimal. The dose-response studies relating vitamin D intake (fortification and supplementation) to S-25(OH)D suggested that an intake of 1-2.5 µg/day will increase the serum concentration by 1-2 nmol/l but this is dependent on the basal concentration with a response being greater when the basal concentration is low.

CONCLUSION

Data show that a S-25(OH)D concentration of 50 nmol/l would reflect a sufficient vitamin D status. Results from this review support that the recommendation in NNR 2004 needs to be re-evaluated and increased for all age groups beyond 2 years of age. We refer to the total intake from food as well as supplements, given minimal sun exposure. Limited sunshine, however, does not reflect the situation for the majority of the Nordic population in the summertime. It should also be emphasized that there are large differences in results depending on assay methods and laboratories measuring 25(OH)D, adding to the uncertainty of determining an appropriate target concentration. Moreover, the dose-response of vitamin D on serum 25(OH)D-concentrations is not well established and is dependent on the basal concentrations, sunshine exposure and dietary intake. We advise that these uncertainties should be taken into account when setting the final Nordic recommendations.

Maternal vitamin D status in type 1 diabetic pregnancy: impact on neonatal vitamin D status and association with maternal glycaemic control

Objective

The first aim of this study was to assess 25-hydroxy vitamin D (25OHD) concentrations in women with type 1 diabetes (T1DM) during pregnancy, post-delivery and also foetal (cord blood) 25OHD concentrations and to examine relationships between these. The second aim of the study was to investigate potential interactions between maternal body mass index (BMI) and foetal vitamin D status. A further study aim was to examine potential relationships between maternal 25OHD and glycosylated haemoglobin (HbA_1c) throughout pregnancy.

Research Design and Methods

This was an observational study of 52 pregnant controls without diabetes and 65 pregnant women with T1DM in a university teaching hospital. Maternal serum 25OHD was measured serially throughout the pregnancy and post-delivery. Cord blood 25OHD was measured at delivery. 25OHD was measured by liquid chromatography tandem mass spectrometry (LC-MS/MS).

Results

Vitamin D deficiency (25OHD <25 nmol/L) was apparent in both the T1DM subjects and controls at all 3 pregnancy trimesters. Vitamin D levels in all cord blood were <50 nmol/L. Maternal 25OHD correlated positively with cord 25OHD at all 3 trimesters in the T1DM group (p = 0.02; p<0.001; p<0.001). 25OHD levels within cord blood were significantly lower for women with diabetes classified as obese vs. normal weight at booking [normal weight BMI <25 kg/m² vs. obese BMI >30 kg/m² (nmol/L±SD); 19.93±11.15 vs. 13.73±4.74, p = 0.026]. In the T1DM group, HbA_1c at booking was significantly negatively correlated with maternal 25OHD at all 3 trimesters (p = 0.004; p = 0.001; p = 0.05).

Conclusion

In T1DM pregnancy, low vitamin D levels persist throughout gestation and post-delivery. Cord blood vitamin D levels correlate with those of the mother, and are significantly lower in obese women than in their normal weight counterparts. Maternal vitamin D levels exhibit a significant negative relationship with HbA_1c levels, supporting a potential role for this vitamin in maintaining glycaemic control.

The association between vitamin D and cognition: a systematic review

Vitamin D insufficiency and deficiency are a major health care problem. The association between vitamin D levels and cognitive function is still under debate. We conducted a systematic review to assess the association between levels of vitamin D and cognition. Therefore, the databases of Embase and Pubmed were searched through June 2012 for observational studies relating vitamin D levels to cognition. Our initial search yielded 2182 articles. After applying exclusion criteria, there were 28 studies eligible for inclusion: 25 cross-sectional and 6 prospective studies (3 studies show cross-sectional as well as prospective data). The main finding of the 25 cross-sectional studies was a statistically significant worse outcome on one or more cognitive function tests or a higher frequency of dementia with lower vitamin D levels or intake in 18 out of 25 (72%) studies, whereas 7 (28%) studies failed to show an association. Four out of 6 (66.7%) prospective studies showed a higher risk of cognitive decline after a follow-up period of 4-7 years in participants with lower vitamin D levels at baseline. In conclusion, this review supports the hypothesis that hypovitaminosis D is associated with worse outcome on one or more cognitive function tests or a higher frequency of dementia in cross-sectional as well as prospective studies. Further studies should focus on the role of vitamin D supplementation in the prevention of cognitive decline in participants with low vitamin D levels.

Vitamin D and the cardiovascular system

Vitamin D, a secosteroid hormone, affects multiple biological pathways via both genomic and nongenomic signalling. Several pathways have potential benefit to cardiovascular health, including effects on parathyroid hormone, the renin-angiotensin-aldosterone system, vascular endothelial growth factor and cytokine production, as well as direct effects on endothelial cell function and myocyte calcium influx. Observational data supports a link between low vitamin D metabolite levels and cardiovascular health. Cross-sectional data shows associations between low 25-hydroxyvitamin D levels and stroke, myocardial infarction, diabetes mellitus, hypertension, and heart failure. Longitudinal data also suggests a relationship with incident hypertension and new cardiovascular events. However, these associations are potentially confounded by reverse causality and by the effects that other cardiovascular risk factors have on vitamin D metabolite levels. Intervention studies to date suggest a modest antihypertensive effect of vitamin D, no effect on serum lipids, a small positive effect on insulin resistance and fasting glucose, and equivocal actions on arterial stiffness and endothelial function. Analysis of cardiovascular event data collected from osteoporosis trials does not currently show a clear signal for reduced cardiovascular events with vitamin D supplementation, but results may be confounded by the coadministration of calcium, and by the secondary nature of the analyses. Despite mechanistic and observational data that suggest a protective role for vitamin D in cardiovascular disease, intervention studies to date are less promising. Large trials using cardiovascular events as a primary outcome are needed before vitamin D can be recommended as a therapy for cardiovascular disease.

Serum 25-hydroxyvitamin D levels, obesity and the metabolic syndrome among Korean children

BACKGROUND AND AIM

Evidence of the relationship between serum vitamin D levels and cardiovascular risk factors in children is limited. We investigated the associations between serum vitamin D levels (25-hydroxyvitamin D [25(OH)D]) and obesity and metabolic syndrome and its components in Korean children.

METHODS AND RESULTS

We recruited 1660, nine-year-old, Korean children (904 boys and 756 girls) who voluntarily participated in this study while being examined during school-based health examinations. We measured anthropometric variables (height and weight), metabolic parameters (blood pressure, fasting plasma glucose, triglyceride, and HDL cholesterol levels) and serum vitamin D levels. We analyzed the data using multivariate logistic regression models. Mean 25(OH)D levels were lower in children defined as obese or abdominally obese (P <0.001). When serum levels of 25(OH)D were divided into quartiles, BMI, waist circumference, and triglyceride levels were lower, and HDL cholesterol levels were higher, as vitamin D levels increased. Using children from the highest quartile of 25(OH)D levels as a referent, the adjusted ORs (95% CI) for obesity in those in the third, second, and lowest quartiles of 25(OH)D levels were 1.55 (1.01-2.40), 1.87 (1.22-2.85), and 2.59 (1.71-3.90), respectively (P for trend <0.001). For abdominal obesity the ORs (CI) were 2.08 (1.20-3.60), 2.32 (1.36-3.95), and 2.96 (1.75-5.00) (P for trend<0.001), and for metabolic syndrome they were 2.60 (1.08-6.30), 4.00 (1.73-9.26), and 4.25 (1.84-9.85), respectively (P for trend <0.05).

CONCLUSIONS

We found low vitamin D levels in Korean children to be associated with obesity and metabolic syndrome. Insufficient serum vitamin D levels in children may be a risk factor of obesity and metabolic syndrome.

Decreased circulating 25-(OH) Vitamin D concentrations in obese female children and adolescents: positive associations with Retinol Binding Protein-4 and Neutrophil Gelatinase-associated Lipocalin

OBJECTIVE

Hypovitaminosis D has been associated with adult as well as childhood obesity. Retinol-binding-protein-4 (RBP-4) and Neutrophil Gelatinase-associated Lipocalin (NGAL) are altered in obese individuals. The aim of this study was to examine circulating 25-(OH) Vitamin D (25-(OH) D) concentrations according to BMI and its associations with RBP-4 and NGAL in female children and adolescents.

DESIGN

Seventy-nine (79) children, aged 8-16 years, were studied and divided into four groups: 19 control (BMI z-score range -2.15 - 1.24), 20 overweight (1.34 - 2.49), 20 obese (2.50 - 2.87) and 20 ultra-obese (3 - 4.37). Patients were derived from a Pediatric Obesity Clinic. Plasma 25-(OH) D, RBP-4 and NGAL concentrations were measured with specific assays.

RESULTS

Plasma 25-(OH) D concentrations were decreased significantly in the ultra-obese (p=0.005) and marginally in the obese group (p=0.05) compared to the control group. In the entire BMI range, Spearman correlations revealed strong positive associations between 25-(OH) D and RBP-4 (r=0.349, p=0.002) and between 25-(OH) D and NGAL (r=0.338, p=0.003).

CONCLUSIONS

25-(OH) D is deficient in a clinical population of obese female children and adolescents, whereas in the entire BMI range 25-(OH) D is associated with RBP4 and NGAL concentrations. Longitudinal studies are needed to reveal the role of these associations in metabolic alterations related to childhood and adolescent obesity and associated metabolic morbidities.

Benefits of ultraviolet-B irradiance and vitamin D in youth

A large and growing body of journal literature reports the health benefits of solar ultraviolet-B (UVB) irradiance and vitamin D. Most of the literature relates to the effects of vitamin D later in life, when chronic diseases are more likely to manifest and when the innate immune system is weaker, leading to increased rates of some infectious diseases. However, a significant body of literature exists on the health effects of solar UVB irradiance and serum 25-hydroxyvitamin D [25(OH)D] concentrations in youth. The goal of this paper is to review representative evidence of health benefits and risks of solar UVB irradiance and vitamin D for those aged from about 5 to 18 years. The topics discussed include physical development, athletic performance, infectious diseases, autoimmune diseases, metabolic syndrome, and cancer. Some of the effects of higher solar UVB irradiance and serum 25(OH)D concentrations are evident in youth, although some may become apparent later in life. This article is part of a Special Issue entitled 'Vitamin D Workshop'.