CAMBRIDGE, UNITED KINGDOM. Researchers at Cambridge University have confirmed that high blood levels of vitamin C (ascorbic acid) protect against stroke. Their study involved 20,649 men and women between the ages of 40 and 79 years when enrolled during the period 1993-1997. None of the participants had suffered a prior stroke. Blood samples were drawn and analyzed for ascorbic acid content at baseline and participants were then followed for an average of 10 years. During this time a total of 448 strokes occurred corresponding to an average annual stroke rate of 0.2%.
After adjusting for the possible effects of gender, age, smoking, BMI, blood pressure, cholesterol, physical activity, diabetes, heart attack, social class, alcohol consumption, and supplement use the researchers conclude that study participants whose blood plasma levels of vitamin C were above 66 micromol/L had a 42% lower risk of stroke than did those whose levels were below 41 micromol/L. They also observed a 17% reduction in stroke for every 20-micromol/L increase in plasma vitamin C concentration. A 20-micromol/L increase in plasma vitamin C concentration can be achieved by adding one additional serving of fruit and vegetables daily.
It is also of interest to note that six times as many study participants in the high plasma vitamin C group were supplementing with vitamin C as compared to those in the low plasma vitamin C group (10.5% vs 1.9%).
Myint, PK, et al. Plasma vitamin C concentrations predict risk of incident stroke over 10 years in 20,649 participants of the European Prospective Investigation into Cancer. American Journal of Clinical Nutrition, Vol. 87, January 1, 2008, pp. 64-69
Editor’s comment: An average reduction in stroke risk of 42% is indeed impressive and compares favourably with the 25-30% relative risk reduction often quoted for aspirin, and the 50-55% reduction attributed to warfarin, especially since increasing one’s vitamin C intake is not associated with any adverse effects. The Cambridge researchers point out that vitamin C has a very short half-life in the blood (about 30 minutes), so spreading one’s intake (whether through foods or supplements) throughout the day is essential.