Plasma 25-hydroxyvitamin D, hormonal contraceptive use, and the plasma proteome in Caucasian, East Asian, and South Asian young adults

Vitamin D deficiency in western dwelling South Asian populations: an unrecognised epidemic

Vitamin D deficiency (25-hydroxyvitamin D; 25(OH)D) is at epidemic proportions in western dwelling South Asian populations, including severe deficiency (<12⋅5 nmol/l) in 27-60% of individuals, depending on season. The paper aimed to review the literature concerning vitamin D concentrations in this population group. Research from the UK and Europe suggests a high prevalence of South Asians with 25(OH)D concentration <25 nmol/l, with most having a 25(OH)D concentration of <50 nmol/l. In Canada, South Asians appear to have a slightly higher 25(OH)D concentration. There are few studies from the United States, South Africa and Australasia. Reasons for vitamin D deficiency include low vitamin D intake, relatively high adiposity, sun exposure avoidance and wearing of a covered dress style for cultural reasons. Possible health effects of deficiency include bone diseases such as rickets and hypocalcaemia in children and osteomalacia in adults. Vitamin D deficiency may also increase the risk of other chronic diseases. Increased fortification of food items relevant to South Asian groups (e.g. chapatti flour), as well as increased use of vitamin D supplements may help reduce this epidemic. Introducing culturally acceptable ways of increasing skin exposure to the sun in South Asian women may also be beneficial but further research is needed to assess the effectiveness of different approaches. There may be a need for a South Asian specific vitamin D dietary intake guideline in western countries. To conclude, vitamin D deficiency is epidemic in South Asians living in western countries and there is a clear need for urgent public health action.

Sex-specific vitamin D effects on blood coagulation among overweight adults

BACKGROUND

Overweight adults are at increased risk for cardiovascular disease and vitamin D deficiency, whereas an important feature to vitamin D physiology is its sex dependence. The aim of this study was to examine whether vitamin D status improvement exerts a sexually dimorphic effect on serum proteins associated with cardiovascular risk among overweight adults.

MATERIALS AND METHODS

Unprocessed serum from age- and BMI-matched men (n = 26) and premenopausal women (n = 24) with vitamin D deficiency and after they achieved sufficiency through a 12-month nutritional intervention was analysed using our previously published depletion-free quantitative proteomics method. Key findings were verified with ELISA. Differentially expressed proteins were subjected to in silico bioinformatics assessment using principal component analysis, hierarchical clustering and Metacore^™ pathway analysis. All mass spectrometry proteomic data are available via ProteomeXchange (identifier: PXD003663).

RESULTS

A total of 282 proteins were differentially expressed after the intervention between men and women (P-value ≤ 0·05), in which the blood coagulation pathway was significantly enriched. In agreement with the proteomics findings, ELISA measurements showed vitamin K-dependent protein C, von Willebrand factor, fibrinogen gamma chain and multimerin-1 proteins, of relevance to blood coagulation, to be differentially affected (P-value ≤ 0·05) between sexes after vitamin D status correction.

CONCLUSIONS

This study identified novel protein-level molecular indicators on the sexually dimorphic effect of vitamin D status correction associated with blood coagulation among overweight adults. These sex-mediated vitamin D effects should be factored in the design and interpretation of vitamin D observational and interventional studies testing cardiometabolic outcomes.

Plasma 25-hydroxyvitamin D, hormonal contraceptive use, and cardiometabolic disease risk in an ethnically diverse population of young adults

OBJECTIVES

The relationship between vitamin D and cardiometabolic disease risk across ethnic groups is unclear, and it is not known whether the use of hormonal contraceptives (HCs), which affect vitamin D metabolism and are also associated with cardiometabolic disease risk, modifies this relationship. Our objectives were to determine the prevalence of vitamin D deficiency (plasma 25-hydroxyvitamin D [25(OH)D] < 30 nmol/L) to assess seasonal variation in concentrations of 25(OH)D, and to examine whether 25(OH)D is associated with cardiometabolic biomarkers across ethnic groups and across men, female HC nonusers, and female HC users in an ethnically diverse population of young adults living in Canada.

METHODS

The study population consisted of Caucasian, East Asian, and South Asian individuals (n = 1384, 69% female) aged 20-29 years. Participants provided overnight fasting blood samples, from which plasma 25(OH)D and cardiometabolic biomarkers were measured. Vitamin D status distributions were compared using χ(2) tests, and analysis of covariance (ANCOVA) was used to examine seasonal variations in 25(OH)D, as well as the association between 25(OH)D and cardiometabolic biomarkers, across groups.

RESULTS

Plasma 25(OH)D concentrations fluctuated seasonally among Caucasians and East Asians and across men, female HC nonusers, and female HC users, but they remained low year-round in South Asians, half of whom were vitamin D deficient. Vitamin D deficiency was associated with higher insulin, homeostasis model assessment-estimated insulin resistance (HOMA-IR), and homeostasis model assessment (HOMA)-beta among Caucasians and East Asians and among men and female HC nonusers and with higher triglycerides among men only. No biomarkers were associated with 25(OH)D among South Asians and female HC users, although nonsignificant trends were observed for higher markers of glycemic dysregulation in those who were vitamin D deficient in both groups.

CONCLUSIONS

Vitamin D deficiency varies between ethnic groups and is particularly high among South Asians, and it is associated with biomarkers of glycemic dysregulation; however, HC use among women may attenuate this association. Given the widespread use of HCs by women throughout the world, a better understanding of the extent to which these medications may modify the relationship between vitamin D and processes related to disease is warranted.

Ability of vitamin D to reduce inflammation in adults without acute illness

In vitro studies and some clinical studies suggest that vitamin D plays an important role in reducing inflammation. The objective of this review was to examine recent evidence that vitamin D status influences the level of inflammation in adults without acute illness or injury. Five large cross-sectional studies and two randomized controlled trials are the focus of this review. Associations between 25-hydroxyvitamin D (25OHD) and inflammation markers are significant and inverse in study populations with low 25OHD levels (<21 ng/mL). They are also inverse in adults with relatively high inflammation levels. These associations in the few available randomized controlled vitamin D intervention trials have been null; this may be because they were not examined in populations with sufficiently low levels of 25OHD or high levels of inflammation.

Genetic variation in the vitamin D receptor, plasma 25-hydroxyvitamin D, and biomarkers of cardiometabolic disease in Caucasian young adults

BACKGROUND/AIMS

Vitamin D regulates gene transcription by binding to the vitamin D receptor (VDR), potentially affecting cardiometabolic disease risk. However, studies of 25-hydroxyvitamin D [25(OH)D] and cardiometabolic disease are inconsistent. Inconsistencies may result from unaccounted for interactions between VDR genetic variants and 25(OH)D. We examined the effect of 25(OH)D on the association between VDR variants and cardiometabolic disease biomarkers.

METHODS

The relationship between 25(OH)D, 24 VDR variants, and 10 cardiometabolic biomarkers was examined in 488 Caucasians aged 20-29 years. Covariate-adjusted general linear models were used to examine the interaction effect of 25(OH)D × VDR on each biomarker. When interactions were significant (p < 0.05), relationships were further examined with analysis of covariance, stratified by tertiles of 25(OH)D and adjusted for multiple comparisons.

RESULTS

In the lowest tertile of 25(OH)D, major allele homozygotes for rs3819545 had higher insulin and HOMA-IR than minor allele carriers (p ≤ 0.002). Fasting insulin and HOMA-IR were lower in the highest than the lowest tertile of 25(OH)D among major allele homozygotes (p < 0.0001), but minor allele carriers had similar levels regardless of vitamin D status.

CONCLUSIONS

We identified 25(OH)D-dependent associations between rs3819545 and glycemic dysregulation biomarkers. Major allele homozygotes with low vitamin D status may be at increased risk of insulin resistance.