A new randomized controlled trial finds that vitamin D supplementation only minimally improves vascular health among women of South Asian origin.
Those with darker skin who migrate to northern latitudes have a much more difficult time producing vitamin D. This is because, with their darker skin, they need more sun exposure to produce the same amount of vitamin D that people with lighter skin produce.
South Asian migrants are also at increased risk of various cardiovascular and metabolic illnesses such as hypertension and diabetes. The reasons behind this are still being researched, and little has been done on effective ways to target this high risk population.
Researchers in the present study speculated that normal cardiovascular risk factors, such as smoking and insulin resistance, didn’t explain the prevalence in South Asian migrants. Might vitamin D play a role? Some research shows vitamin D plays a role in cardiovascular health.
The researchers conducted a randomized controlled trial to determine the effects of short term vitamin D supplementation on cardiovascular health markers. Eighty-four women of South Asian origin living in the United Kingdom were approached for the study. Fifty women entered the trial and were randomly assigned to a supplement group or placebo group.
Baseline serum 25(OH)D levels and vascular health markers were measured. Vascular health was measured using flow mediated dilation, measuring arterial stiffness, and through blood samples which looked at Plasminogen activator inhibitor-1 antigen (PAI-1) and tissue plasminogen activator antigen (t-PA) levels.
PAI-1 and t-PA are important markers in vascular health. T-PA is an especially important protein involved in the breakdown of blood clots. It is often used as an important medicine administered for stroke and head trauma. Reduced t-PA activity, therefore, could lead to buildup of blood clots and further the risk of atherosclerosis, a common arterial stiffening in cardiovascular events. Despite t-PA improving blood clot breakdown, high levels of PAI-1 and t-PA, together, may be associated with cardiovascular disease.
The researchers administered a single 100,000 IU vitamin D dose to the participants, or a placebo dose. After 4 and 8 weeks, the researchers measured cardiovascular health markers again. This is what they found:
- Vitamin D levels in the supplement group increased significantly. Mean baseline levels were 10.8 ng/ml. At 4 weeks mean vitamin D levels increased to 17.2 ng/ml, and at 8 weeks mean levels increased to 21.2 ng/ml.
- After 8 weeks, the vitamin D group experienced significant reductions in t-PA and PAI-1 levels compared to placebo.
- There were no significant changes in any other vascular, metabolic, or inflammatory markers.
The researchers concluded,
“We found no effect of a single large dose of oral vitamin D3 on a range of vascular and metabolic markets in this trial. Small reductions were however seen in t-PA and PAI-1 levels after vitamin D supplementation; these reductions were seen at 4 weeks and became significant by 8 weeks.”
The research team noted that while South Asians living in the UK have high rates of vascular disease, the participants they recruited lacked any sort of baseline disease. This may help explain why vitamin D did not improve vascular health in this study. Additionally, the single 100,000 IU of vitamin D administered was not effective in bringing vitamin D levels to at least 30 ng/ml.
They call for future studies to include participants with high risk markers such as elevated blood pressure or high levels of insulin resistance.
Witham, M., et. al. Effects of short-term vitamin D supplementation on markers of vascular health in South Asian women living in the UK – A randomized controlled trial. Atherosclerosis, 2013.