The greatest benefits of the supplements were observed in people with vitamin D deficiency, researchers from the University of Kansas report in the American Journal of Cardiology.
The findings could have implications for current guidelines, said the researchers, since supplements providing at least 1,000 International Units (IU) per day may be needed to avoid deficiency. The Institute of Medicine recently increased the recommended daily allowance (RDA) to 600 IU.
“Because vitamin D deficiency is widespread, strategies directed at population-based supplementation programs could prove beneficial,” wrote the researchers.
“To date, however, prospective studies evaluating vitamin D supplementation are few and have not consistently shown benefit. It is possible that the lack of benefit in these studies resulted from suboptimal levels of vitamin D supplementation or other unknown factors.
“Many previous studies of vitamin D supplementation have used doses of 400 to 800 IU, which might not be adequate to ensure optimal serum levels, with more appropriate daily supplement doses suggested as 1,000 to 2,000 IU.”
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 and -2 diabetes.
Led by James Vacek, MD, the Kansas-based researchers studies how vitamin D levels and supplementation may affect disease risk and mortality in 10,899 people with an average age of 58. Participants were classified as vitamin D deficient if their blood levels of 25(OH)D were lower than 30 ng/ml.
Results showed that the mean vitamin D level was 24 ng/ml, and that 70% of the people were deficient.
Vacek and his co-workers note that deficiency was associated with significantly higher incidence of cardiovascular-related diseases, such as hypertension, coronary artery disease, and diabetes.
In addition, the risk of all-cause mortality was 164% higher in people with vitamin D deficiency, they noted.
On the other hand, vitamin D supplements were associated with a 61% increase in survival in this study population.
“Additional investigation with long-term prospective studies of various vitamin D dosage levels in both healthy and diseased populations are indicated to firmly establish the role of vitamin D supplementation on overall outcomes and mortality,” wrote the researchers.
“Our study suggests a significant association of vitamin D supplement use and improved survival in deficient subjects, supporting the potential benefit of this intervention.”
Source: American Journal of Cardiology
Volume 109, Number 3, Pages 359-363, doi: 10.1016/j.amjcard.2011.09.020
“Vitamin D deficiency and supplementation and relation to cardiovascular health”
Authors: J.L. Vacek, S.R. Vanga, M. Good, S.M. Lai, D. Lakkireddy, P.A. Howard