Conclusions Vitamin D supplementation did not improve EF .
The significant effect of vitamin D in diabetics and a tendency for an association with BMI may indicate a role of excess adiposity and insulin resistance in modulating the effects of vitamin D on vascular function .
Abstract Background In addition to regulating calcium homoeostasis and bone health , vitamin D influences vascular and metabolic processes including endothelial function ( EF ) and insulin signalling .
Vitamin D supplementation and endothelial function in vitamin D deficient HIV-infected patients: a randomized placebo-controlled trial.
BACKGROUND Studies suggest that vitamin D deficiency is a risk factor for cardiovascular disease and diabetes . Vitamin D deficiency is prevalent in HIV patients but the effect of vitamin D supplementation on cardiovascular risk in this population is unknown . METHODS We conducted a r and omized , double-blind , placebo-controlled trial among 45 HIV-infected adults in Clevel and ( OH , USA ) on stable antiretroviral therapy with durable virological suppression and a baseline serum 25-hydroxyvitamin D level of ≤20 ng/ml . Participants were r and omized 2:1 to vitamin D3 4,000 IU daily or placebo  for 12 weeks . The primary outcome was a change in flow-mediated brachial artery dilation ( FMD ) . RESULTS Baseline demographics were similar except for age ( vitamin D versus placebo , mean ±sd 47 ±8 versus 40 ±10 years ; P=0.009 ) . Both groups had reduced FMD at baseline ( median values 2.9 % [ IQR 1.6 - 4.8 ] for vitamin D versus 2.5 % [ IQR 1.7 - 6.4 ] for placebo ; P=0.819 ) . Despite an increase in the concentration of serum 25-hydroxyvitamin D from baseline to 12 weeks ( 5.0 ng/ml [ IQR -0.9 - 7.4 ] versus -1.9 ng/ml [ IQR -4.0 - 0.1 ] for vitamin D versus placebo , respectively ; P=0.003 ) , there was no difference in FMD change ( 0.55 % [ IQR -1.05 - 2.13 ] versus 0.29 % [ IQR -1.61 - 1.77 ] ; P=0.748 ) . Vitamin D supplementation was associated with a decrease in total and non-high-density lipoprotein cholesterol , and an increase in indices of insulin resistance . CONCLUSIONS Among HIV-infected individuals with vitamin D deficiency , supplementation with 4,000 IU vitamin D3 daily for 12 weeks modestly improved vitamin D status and cholesterol but worsened insulin resistance without change in endothelial function . The mechanisms of resistance to st and ard doses of vitamin D and the complex role of vitamin D in glucose metabolism in this population require further investigation
Conclusions Vitamin D supplementation did not improve EF .
The significant effect of vitamin D in diabetics and a tendency for an association with BMI may indicate a role of excess adiposity and insulin resistance in modulating the effects of vitamin D on vascular function .
Abstract Background In addition to regulating calcium homoeostasis and bone health , vitamin D influences vascular and metabolic processes including endothelial function ( EF ) and insulin signalling .