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."