Diet clearly plays a role in controlling hypertension and overweight, two potent risk factors for stroke, with multiple nutrients, including antioxidants, minerals, fat, and fiber, likely coming into play. A study reported in a recent issue of the journal Stroke adds to what clinicians know about the link between one antioxidant -- vitamin C -- and the long-term risk of stroke.

Data analysis

Researchers in Finland measured serum vitamin C levels in 2,419 middle-aged male participants of the ongoing Kuopio Ischemic Heart Disease Risk Factor Study. Men with a history of stroke were excluded from this analysis. Participants were followed for up to 10 years; the outcome of interest was development of stroke.

During the follow-up period 120 participants suffered a stroke. After controlling for potential confounders -- including age, BMI, smoking, blood pressure, and serum cholesterol -- the researchers found that men with a serum vitamin C level less than 28.4 µmol/liter were more than twice as likely as those with levels greater than 64.96 µmol/liter to experience a stroke (RR=2.10, 95% CI 1.17-3.80).

Interaction of multiple factors

Using a stepwise Cox model, the researchers then looked for a relationship between hypertension and overweight, serum vitamin C status, and risk of stroke. They found an interaction between hypertension and vitamin C status. Hypertensive men with plasma vitamin C levels less than 28.4 µmol/liter were at markedly increased risk for stroke (RR=2.61, 95% CI 1.52-4.48). Likewise, men with a BMI greater than 25 (an indication of overweight) who also had low serum vitamin C levels were more than twice as likely as normal weight men with high vitamin C levels to suffer a stroke (RR=2.69, 95% CI 1.48-4.90).

Proposed pathway

The authors of this study say that these results point to poor vitamin C status as a compounding factor in stroke risk, particularly among hypertensive and overweight men. They suggest a pathway that might explain this effect. As a potent antioxidant, vitamin C may help to control the oxidation that contributes to endothelial dysfunction, a step in the development of hypertension. To support this view, they point to several key studies that show a link between vitamin C status and risk of hypertension. Vitamin C may also figure into the research that has shown a definitive link between intake of fruits and vegetables and a reduced risk of hypertension.

The authors admit, however, that it is very difficult to analyze the effect of vitamin C independent of all the other nutrients that contribute to good health. A diet that is high in fruits and vegetables supplies a variety of antioxidants and phytochemicals, as well as potassium and magnesium. This type of diet also tends to be high in fiber and lower in fat and sodium. All of these factors likely contribute to some extent to the reduced stroke risk attributed, in this study, to vitamin C.

Advice to patients

This study adds yet more weight to the claim that a healthful diet should include at least five servings a day of fruits and vegetables. This becomes even more pressing with advancing age, as the body contends with the accumulating effects of oxidative stress. Remind your patients that it's never too late to eat more healthfully. Prompt them to take a look at what they usually eat and see if there is room for more fruits and vegetables, especially those rich in vitamin C.