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Vitamin D deficiency is highly prevalent among non-western immigrants in The Netherlands and associated with poor physical performance. The aim of this study was to assess the effect of vitamin D supplementation on physical performance, exercise capacity, and daily physical activity in vitamin D-deficient, overweight non-western immigrants. A randomized double-blind, placebo-controlled trial was conducted to assess the effect of vitamin D on physical performance. A total of 130 participants were included. Eligibility criteria included overweight (BMI >27 kg/m²), 25-hydroxy vitamin D (25(OH)D) ≤50 nmol/l, and an age range of 20–65 years. The intervention group received 1200 IU vitamin D3 daily for 4 months; the control group received placebo. Both groups received 500 mg calcium daily. Outcome measures included physical performance (physical performance score), exercise capacity (a 6-min walk test (6-MWT)), and daily physical activity (questionnaire and accelerometer). There was no significant effect on physical performance, exercise capacity, or physical activity in the intention to treat analysis. In an explorative post hoc analysis restricted to participants reaching a serum 25(OH)D concentration of >60 nmol/l after intervention, there was an improvement of 19 m in the 6-MWT compared with the control group (P=0.053). Moderate dose vitamin D supplementation did not significantly improve physical performance, exercise capacity, or physical activity. However, when 25(OH)D concentrations reached >60 nmol/l after intervention, there was a borderline significant improvement in exercise capacity. Although the clinical relevance is not clear, this is a promising result, as all participants were overweight and did not improve their overall activity levels.

Maternal vitamin D deficiency is linked to adverse pregnancy outcomes including spontaneous preterm birth (SPB). Placental corticotropin-releasing hormone (CRH) has been proposed to be part of a clock that governs the length of gestation in humans, with elevated maternal serum levels predicting early delivery. In this study, we test the hypothesis that vitamin D could contribute to the prevention of preterm labor by inhibiting CRH and other pro-labor mediators. The biological activity of vitamin D occurs via two pathways: non-genomic and genomic responses, both of which involve binding of 1,25-dihydroxyvitamin D (1,25(OH)2D), the active metabolite of vitamin D binding to the vitamin D receptor (VDR). By using chromatin immunoprecipitation followed by sequencing (ChIP-seq), we found that 1,25(OH)2D stimulates association of VDR with a number of miRNA genes including MIR181B2 and MIR26B, and their mature products miR-181b-5p and miR-26b-5p are predicted to target CRH and cyclooxygenase-2 (COX-2) mRNA at 3′-untranslated region (UTR), respectively. We performed RT-qPCR analysis to validate that expression of mature miR-181b-5p and miR-26b-5p in term human syncytiotrophoblast increased in response to treatment with 1,25(OH)2D. miR-181b-5p- or miR-26b-5p-mediated inhibition of CRH or COX-2 was further assessed by the use of miRNA mimics/inhibitors and a luciferase reporter assay. Taken together, this study has identified novel mechanisms by which vitamin D downregulates pro-labor genes and could lower the risk of preterm delivery.

A systematic review of publications addressing change in vitamin D status (25-hydroxyvitamin D (25OHD)) after exposure to UV radiation identified 2001 independent peer-reviewed publications. Of these, 21 used artificial sources of UV radiation, met all inclusion criteria and were quality assured; 13 publications used solar radiation and met sufficient inclusion criteria to be retained as supporting evidence; 1 further included publication used both solar and artificial sources. The review consistently identified that low dose, sub-erythemal doses are more effective for vitamin D synthesis than doses close to a minimum erythema dose; increasing skin area exposed increases the amount of vitamin D synthesised although not necessarily in a linear manner; constant dosing leads to a dose-dependent plateau in 25OHD, and dose–response is greatest at the start of a dosing regime; there is a large interpersonal variation in response to UV exposure. Fourteen of the studies using artificial sources of radiation were used to determine a dose–response relationship for change in 25OHD on whole-body exposure to repeated sub-erythemal doses of UV radiation, taking the form Δ25OHD (nmol/L) = A ln(standard vitamin D dose) + B. This helps quantify our understanding of UV as a source of vitamin D and enables exposure regimes for safe synthesis of vitamin D to be assessed. Specific studies of people with pigmented skin (Fitzpatrick skin types 5 and 6) were rare, and this dose–response relationship is only applicable to white-skinned individuals as skin type is a determinant of response to UV radiation. Findings provide information for vitamin D guidance updates.

To assess the effect of vitamin D supplementation on parameters of insulin sensitivity/resistance (IS/IR) and insulin secretion in subjects with polycystic ovarian syndrome (PCOS). A prospective double-blind randomized control trial was conducted to assess the effect of vitamin D on insulin kinetics in women with PCOS. The trial was conducted in a tertiary care research hospital. A total of 36 subjects with PCOS, aged 18–35 years, were included in this study. Vitamin D3 4000 IU/day versus placebo was given once a month for 6 months and both groups received metformin. IS (by whole-body IS index or Matsuda index), IR (by homeostasis model assessment IR (HOMA-IR)), and insulin secretion (by insulinogenic index; II₃₀) were the main outcome measures. Secondary outcome included blood pressure (BP), lipid profile, disposition index (DI), and vascular stiffness. Out of 36 subjects who consented, 32 completed the study. Subjects were randomized into two groups: group A (n=15; metformin and vitamin D 4000 IU/day) or group B (n=17; metformin and placebo). Oral glucose tolerance tests with 75 g glucose were carried out at baseline and 6 months after supplementation. Hypovitaminosis D was observed in 93.8% of all subjects with mean serum 25 hydroxy vitamin D level of 7.30±4.45 ng/ml. After 6 months of vitamin D supplementation, there was no significant difference in any of the parameters of IS/IR (area under curve (AUC)–glucose, AUC–insulin, insulin:glucose ratio, HOMA-IR, Matsuda index, insulinogenic index, and DI), II₃₀, and cardiovascular risk factors between the two groups. Supplementation of vitamin D, at a dose of 4000 IU/day for 6 months, did not have any significant effect on parameters of IS/IR and insulin secretion in subjects with PCOS.

The measurement of vitamin D metabolites aids in assessing vitamin D status and in diagnosing disorders of calcium homeostasis. Most laboratories measure total 25-hydroxyvitamin D (25(OH)D), while others have taken the extra effort to measure 25(OH)D₂ and 25(OH)D₃ separately and additional metabolites such as 1,25-dihydroxyvitamin D and 24,25-dihydroxyvitamin D. The aim of this review is to provide an updated overview of the main markers of vitamin D metabolism, define the intended measurands, and discuss the advantages and disadvantages of the two most widely used assays, automated assays and liquid chromatography–tandem mass spectrometry (LC-MS/MS). Whether using the easy and fast automated assays or the more complex LC-MS/MS, one should know the pitfalls of the used technique in order to interpret the measurements. In conclusion, automated assays are unable to accurately measure 25(OH)D in all patient groups, including persons using D₂. In these cases, an LC-MS/MS method, when appropriately developed and standardized, produces a more reliable measurement.

Data on dietary calcium and vitamin D intake from Latin America are scarce. We explored the main correlates and dietary sources of calcium and vitamin D in a probabilistic, population-based sample from Colombia. We studied 1554 participants aged 18–75 from five different geographical regions. Dietary intake was assessed by employing a 157-item semi-quantitative food frequency questionnaire and national and international food composition tables. Daily vitamin D intake decreased with increasing age, from 230 IU/day in the 18–39 age group to 184 IU/day in the 60–75 age group (P -trend < 0.001). Vitamin D intake was positively associated with socioeconomic status (SES) (196 IU/day in lowest vs 234 in highest SES, P-trend < 0.001), and with educational level (176 IU/day in lowest vs 226 in highest education level, P-trend < 0.001). Daily calcium intake also decreased with age, from 1376 mg/day in the 18–39 age group to 1120 mg/day in the 60–75 age group (P -trend < 0.001). Calcium intake was lowest among participants with only elementary education, but the absolute difference in calcium intake between extreme education categories was smaller than for vitamin D (1107 vs 1274 mg/day, P-trend = 0.023). Daily calcium intake did not correlate with SES (P -trend = 0.74). Eggs were the main source of overall vitamin D, albeit their contribution decreased with increasing age. Dairy products contributed at least 48% of dietary calcium in all subgroups, mostly from cheese-containing traditional foods. SES and education were the key correlates of vitamin D and calcium intake. These findings may contribute to shape public health interventions in Latin American countries.