Increased vitamin D intake linked with lower stroke risk over 34 years of follow-up
Friday, May 25, 2012. An article published on May 24, 2012 in the American Heart Association journal Stroke reports a protective effect for greater vitamin D intake against the risk of ischemic stroke in Japanese-American men. To the authors' knowledge, there has only been one other longitudinal cohort study (which had fewer subjects and a shorter follow-up) that evaluated dietary vitamin D intake and stroke risk.
Gotaro Kojima, MD of the University of Hawaii and colleagues utilized data obtained from 7,385 Japanese-American men residing in Oahu who were between the ages of 45 to 68 upon enrolling in the Honolulu Heart Program between 1965 and 1968. Dietary recall interviews conducted upon enrollment were analyzed for the intake of vitamin D from food. (The authors note that regular use of dietary supplements was uncommon in the 1960s.)
Over the 34-year follow-up period, stroke was documented in 960 subjects. For men whose vitamin D intake was among the lowest 25 percent of participants, the adjusted risk of stroke was 22 percent higher than the risk experienced by those whose intake was among the top 25 percent. When stroke was analyzed by type, the risk of thromboembolic stroke was 27 percent higher for those whose vitamin D intake was lowest in comparison with the highest group, and no significant association was found between the vitamin and the risk of hemorrhagic stroke.
"Our study confirms that eating foods rich in vitamin D might be beneficial for stroke prevention," concluded Dr Kojima, who is a geriatric medicine fellow at the University of Hawaii's John A. Burns School of Medicine.
In their discussion of the findings, the authors remark that vitamin D deficiency is associated with vascular disease risk factors such as hypertension, insulin resistance, diabetes, and inflammation, and they note that the vitamin influences numerous genes involved in cellular proliferation and blood vessel formation. While sunlight is considered by some individuals to be the best source of vitamin D, Dr Kojima remarked that synthesizing the vitamin from sunlight becomes more difficult with age, making supplementation or increased intake of vitamin D-fortified foods advisable for older men and women. "Based on the results of this and other epidemiological studies, higher vitamin D intake or vitamin D supplementation may be beneficial for stroke prevention," the authors conclude. "Large prospective placebo controlled randomized studies are needed to confirm this relationship. We await the results of VITAL, the Vitamin D and Omega-3 Trial, the first large randomized clinical trial of vitamin D supplementation with/without fish oil launched in 2010 to study cardiovascular diseases, cancer, and other chronic diseases."
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Having an optimal serum level of vitamin D appeared to reduce the risk of dying from cardiovascular disease or any cause in men and women with metabolic syndrome who were followed for a period of 7.7 years. The finding was described in an article published online on March 7, 2012 in the journal Diabetes Care.
G. Neil Thomas, PhD of the University of Birmingham in England and his associates evaluated data from 1,801 men and women with metabolic syndrome who were enrolled in the Ludwigshafen Risk and Cardiovascular Health study, which included patients referred for coronary angiography from 1997 to 2000. Fasting blood samples were analyzed for 25-hydroxyvitamin D [25(OH)D], glucose and other factors. Four hundred sixty-two deaths occurred over follow up, of which 267 were due to cardiovascular causes.
For those whose vitamin D levels were classified as optimal at over 75 nanomoles per liter, there was a 75 percent lower risk of mortality over follow-up compared to the risk experienced by those who were categorized as severely deficient with levels of less than 25 nanomoles per liter. The risk of dying of cardiovascular causes was 67 percent lower for those with optimal levels of vitamin D, however, this reduction was limited to sudden death and congestive heart failure, for which this group had 85 percent and 37 percent lower risks compared to severely deficient subjects.
"In summary, 25(OH)D levels were dose-dependently associated with a robust reduction in all-cause and cardiovascular mortality in subjects with the metabolic syndrome," the authors conclude. "We hope these findings will spur interventional randomized, controlled trials to confirm the effects of vitamin D on mortality and, if positive, help establish recommendations for supplementation in these subjects."
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