DALLAS, Sept. 22--Diets rich in fruits, vegetables and whole grain cereals may reduce a person's risk of stroke, especially in individuals with high blood pressure, according to a study in today's Circulation: Journal of the American Heart Association.
"This beneficial effect appears to be due to the high potassium content of these diets, but other components of fruits and vegetables may also contribute to the reduced risk of stroke," says Alberto Ascherio, M.D., Dr.P.H., lead author of the study and associate professor of nutrition and epidemiology at Harvard School of Public Health.
In a study of almost 44,000 men, researchers found that individuals in the top fifth of dietary potassium intake had a 38 percent lower risk of stroke than those in the bottom fifth. The major difference between the diets of the two groups was in their consumption of fruits and vegetables -- about nine servings daily in the highest potassium group compared with four in the lowest. Sources of dietary potassium include tomatoes, spinach, bananas, oranges and other fruits and vegetables.
"While the data do not prove a causal relationship, there is strong support for a stroke- preventive effect from diets rich in potassium, magnesium and cereal fiber. This was found to be particularly true in individuals with high blood pressure, further suggesting that high-potassium diets might be beneficial in this segment of the population," says Ascherio.
The results of smaller investigations and animal studies have suggested that high levels of dietary potassium could help reduce the risk of stroke. Ascherio and his research colleagues set out to determine whether these findings would still hold true in a larger study.
Researchers questioned 43,738 men who were part of the Health Professionals Follow-up Study, a dietary investigation of men who were free of heart disease, diabetes and had not had a stroke. The men were asked how many times a day during the past year they had eaten any of 131 different foods and whether they used vitamin and mineral supplements during the past year. Researchers chose foods for the list of 131 that provided a comprehensive assessment of each individual's diet. In addition, researchers asked about the use of potassium and magnesium supplements. Follow-up questionnaires were given every two years to update dietary information and potential risk factors for heart disease and to identify newly diagnosed strokes. During the eight-year study 328 individuals had strokes.
Men without high blood pressure whose diets were high in magnesium and cereal fiber also had a reduced risk of stroke when compared to men who ate lower levels of these nutrients. Those with high intakes of magnesium had a 30 percent decreased risk of stroke and those with high intakes of cereal fiber had a 40 percent decreased risk compared with those who ate low levels of these nutrients.
Individuals who had high blood pressure (8,520 men) and were taking potassium supplements (about one gram per day) had a 60 percent reduced risk of stroke when compared to those with high blood pressure who weren't taking supplements. Potassium supplements are often prescribed to individuals taking diuretics. The drugs are used to treat high blood pressure, but they can deplete the body of potassium.
"Even a person taking potassium-depleting diuretics can increase their potassium levels through dietary means," he says. "In this group, however, physicians may consider the use of supplements.
"Diuretics are extremely effective in reducing the risk of stroke in people with high blood pressure and it appears that their effectiveness can be further increased with adequate potassium intake," Ascherio says.
It is not necessary, Ascherio says, for people not on these drugs to take potassium supplements. "Two tomatoes and one serving of cooked spinach provide about one gram of potassium," he says. "This is the typical amount contained in supplements.
Ascherio recommends that people with high blood pressure consult a physician before using supplements because they may be harmful, especially for people with kidney problems.
Though other studies have shown that a high potassium diet may reduce high blood pressure, Ascherio says the decrease in stroke did not appear to be due to changes in blood pressures. "Blood pressure changes that were observed were too small to cause such a dramatic decrease in stroke risk," says Ascherio. Co-authors include: E.B. Rimm, Sc.D.; M.A. Herman, M.D.; M. J. Stumper, M.D., Dr.P.H.; W.C. Willett, M.D., Dr.P.H.; I. Kawachi, M.D., Dr.P.H.; and E.L. Giovannucci, M.D., Sc.D.