DALLAS, Oct. 6 – Individuals with high blood levels of vitamin C have significantly reduced risk of stroke, according to a long-term study reported in the October issue of Stroke: Journal of the American Heart Association.
Higher intake of fruits, vegetables and other foods rich in vitamin C and potassium have been associated with lower stroke rates in previous studies.
“To my knowledge, this is the first prospective study to make the correlation between vitamin C in the bloodstream and incidence of stroke,” says author Tetsuji Yokoyama, M.D., research associate in epidemiology at the Medical Research Institute of Tokyo Medical and Dental University. “The risk of stroke was inversely related to vitamin C in the bloodstream and frequency of vegetable consumption.”
The researchers examined 880 men and 1,241 women in rural Japan which were divided into four groups according to the level of vitamin C in their blood. Among the participants, 196 strokes occurred during a 20-year period beginning in 1977.
“The risk of stroke was 70 percent higher among those in the lowest quarter than those in the highest,” says Yokoyama.
When researchers examined strokes based on the number of days per week the participants ate fruits and vegetables, they found a similar relationship. The clearest association was for vegetable consumption.
“The risk of all types of stroke was 58 percent lower among those who consumed vegetables six to seven days per week, compared to those who only consumed them up to two days a week,” notes Yokoyama.
Higher concentrations of vitamin C in the blood provided benefits even in patients with other risk factors, such as high blood pressure, heavier alcohol consumption, smoking or lower physical activity. However, these risk factors did reduce the benefits somewhat. The reasons are unclear, but smoking and alcohol may interfere with vitamin C absorption or metabolism.
“Thus, we recommend healthy behaviors such as eating fruits and vegetables frequently, not smoking, avoiding excess drinking, and being moderately physically active,” Yokoyama says.
Although blood vitamin C levels also rise with vitamin C supplements, it was rare to take vitamin supplements in this Japanese community when the study began and therefore researchers cannot confirm the same benefit from them.
The 196 strokes that occurred included 109 cerebral infarctions – a stroke in which blood flow to the brain is blocked – and 54 hemorrhagic strokes, which occur when an artery in the brain bursts. Another 33 strokes were of undetermined typed.
Because a risk reduction was observed in both types of stroke, Yokoyama says the responsible mechanism probably extends beyond vitamin C’s known antioxidant effects. Cerebral infarctions are considered to be the result of atherosclerosis, the build-up of fatty deposits in arteries. Antioxidants can prevent the buildup. Hemorrhagic stroke, on the other hand, results from a ruptured blood vessel in the brain.
“One plausible explanation is that vitamin C may be a marker for higher intake of other nutrients which may protect against stroke,” explains Yokoyama.
Although widespread screening to determine blood vitamin C levels might eventually be a good idea, it is too early to make such a recommendation, Yokoyama suggests.
The researchers are preparing a database to analyze the association between blood levels of vitamin C and subsequent incidence of heart attack in the same population.
Co-authors are Chigusa Date, Ph.D.; Yoshihiro Kokubo, M.D.; Nobuo Yoshiike, M.D.; Yasuhiro Matsumura, Ph.D.; and Heizo Tanaka, M.D.
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