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Vitamin D deficiency is well known to be associated with osteoporosis, but two studies published this week have shown that lack of the “sunshine vitamin” also increases the risk of heart disease and is linked to poorer prognosis for some cancers.
A follow-up study of 1739 offspring of the original participants in the Framingham heart study, with no cardiovascular disease, showed that those with low concentrations of vitamin D (below 15 ng/ml) had twice the risk of a first cardiovascular event, such as a myocardial infarction, heart failure or stroke, in the five years from baseline than those with higher concentrations (Circulation doi: 10.1161.circulationaha.107.706127).
After adjusting for the usual cardiovascular risk factors, including high cholesterol concentrations, diabetes, and hypertension, the researchers found that risk of a cardiovascular event remained 62% higher in people with low vitamin D concentrations (hazard ratio 1.62 (95% confidence interval 1.11 to 2.36). The risk was greatest in people with hypertension; in this group the risk of a cardiovascular event among those with a low vitamin D concentration was twice that among those with higher concentrations (hazard ratio 2.13 (1.3 to 3.48)).
Thomas Wang, a resident in internal medicine at Massachusetts General Hospital, Boston, and the study’s lead author, said, “A growing body of evidence suggests that low levels of vitamin D may adversely affect the cardiovascular system.” He noted that vitamin D receptors are widely distributed, occurring in the vascular smooth muscle and endothelium.
“Our data raise the possibility that treating vitamin D deficiency, via supplementation or lifestyle measures, could reduce cardiovascular disease,” he said, although he cautioned that further studies are needed to show causation. The American Heart Association recommends that everyone, including people with coronary heart disease, should eat a healthy diet that is based on a variety of foods in moderation, including those rich in vitamin D such as milk and oily fish, rather than supplements.
Vitamin D deficiency was common in the study participants, with 28% of people having concentrations below 15 ng/ml and 9% having concentrations below 10 ng/ml. Only 10% of the study sample had a concentration above 30 ng/ml, considered the optimal level for bone metabolism. Dr Wang warned that the study had important public health implications, as vitamin D deficiency is common, with moderate to severe deficiency affecting 20% to 30% of the US population. Much of this deficiency is due to lack of sun exposure, pigmented skin, which prevents penetration of the sun’s rays, and inadequate dietary intake of foods containing vitamin D.
A second study says that warnings to avoid sunlight because of the risk of skin cancer from solar radiation may have to be balanced against the health benefits of exposure to sunlight, given that vitamin D improves outcomes in patients with major internal cancers, including prostate, breast, and colon cancers.
The study calculated the average yield of vitamin D in people in different locations around the world and compared this with the age adjusted incidence of a range of cancers and mortality from those cancers (Proceedings of the National Academy of Sciences of the United States of America doi: 10.1073/pnas.0710615105). The study showed that vitamin D production generated by solar radiation was 3.4 times greater in countries below the equator than in the United Kingdom and 4.8 times greater than in Scandinavia. Although the incidences of major internal cancers were higher in countries at lower latitudes, the survival prognosis improved significantly.
The authors said that the better prognosis may be due to greater exposure to sunlight, given that previous research has shown that optimal concentrations of vitamin D protect against internal cancers. They concluded, “Epidemiological data for cancer argue for an overall positive role of sun-induced vitamin D. Authorities should pay attention not only to skin cancer research, but also to research on vitamin D-sun-health relationships occurring worldwide.”
Limiting sun exposure and using a sunscreen, as recommended in many skin cancer campaigns, reduces the production of vitamin D induced by exposure to sunlight.