A ten-year study of a Japanese rural community (published in the October issue of
The Shibata study, conducted by a multicenter team of Japanese researchers, followed a cohort of 880 men and 1,241 women who were free of stroke in 1977. Subjects were stratified into four groups according to serum vitamin C levels, and interviewed yearly to determine incidence of stroke. Strong inverse associations were observed between serum vitamin C concentration and all stroke (sex-adjusted and age-adjusted hazard ratios were 0.93, 0.72 and 0.59, respectively, for the second, third and fourth quartiles compared with the first quartile;
When the researchers reanalyzed the stroke incidence data according to number of days per week the subjects ate fruit and vegetables, they found a similarly strong association. "The risk of all types of stroke was 58% 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 lead researcher Yokoyama. Additional adjustments for blood pressure, serum total cholesterol, body mass index, physical activity, smoking, alcohol drinking, antihypertensive medication, atrial fibrillation and history of ischemic heart disease did not attenuate these associations markedly.
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, whereas hemorrhagic stroke 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," the authors suggest. 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.