Bananas typically contain 450 mg of potassium and are naturally free of fat, cholesterol and sodium.
The study, published in the American Heart Association's (AHA) journal Stroke, also suggests that postmenopausal women derive greater benefit from potassium-rich foods if they do not have high blood pressure.
Stroke is one of the leading causes of death in the US, and 60% of all stroke cases are female. Potassium has previously been associated with a lower risk of stroke, but up until now there has been little data regarding its effects in older women or on different types of stroke.
"Previous studies have shown that potassium consumption may lower blood pressure. But whether potassium intake could prevent stroke or death wasn't clear," explains Sylvia Wassertheil-Smoller, PhD, senior author of the study from Albert Einstein College of Medicine, Bronx, NY.
Potassium is used by the body to maintain a normal water balance between cells and body fluids. This element is also essential for muscle contraction, how nerves respond to stimulation and for the efficient working of cellular enzymes.
Unfortunately, the study indicates that many older American women are not getting the recommended amount of potassium in their diets - at least 4,700 mg of potassium daily, according to the US Department of Agriculture.
"Only 2.8% of women in our study met or exceeded this level," says Wassertheil-Smoller. "The World Health Organization's daily potassium recommendation for women is lower, at 3,510 mg or more. Still, only 16.6% of women we studied met or exceeded that."
Investigating potassium intake
The researchers followed a total of 90,137 postmenopausal women, aged from 50 to 79, for an average of 11 years. During this period, they monitored how much potassium the participants consumed as well as the incidence of different stroke types and death.
All of the women were stroke-free when the study began. Their average dietary potassium intake was 2,611 mg per day, and the researchers based the results of the study on potassium intake from foods rather than supplements.
The researchers found that the women who consumed the most potassium (more than 3193.6 mg a day) were 16% less likely to have an ischemic stroke and 12% less likely to have a stroke in general than the women who ate the least (less than 1925.5 mg of potassium a day).
The women who ate the most potassium were also less likely to die during the follow-up period than those who had the lowest potassium consumption.
Hypertension had an impact on the results. Among the participants who did not have hypertension, the women who ate the most potassium were 27% less likely to suffer an ischemic stroke and 21% less likely to have a stroke in general than those who ate the least potassium.
The women who did suffer from hypertension did not lower their stroke risk through a high intake of potassium, although they did have a lower risk of death during the follow-up period than those who ate a lower amount of potassium.
'Another reason to eat fruit and vegetables'
From these findings, the researchers suggest that a diet featuring a higher consumption of potassium could be more beneficial before hypertension develops. They also note that a lack of evidence for an association between potassium intake and hemorrhagic stroke may be due to the low incidence within the study.
The authors acknowledge that their study is an observational one focusing on potassium, and so caution should be used when interpreting their findings for causation. For instance, sodium consumption may have had an impact on the participants' risk of stroke and death during the follow-up period.
Despite the study's limitations, Wassertheil-Smoller says their findings suggest that women should eat more potassium-rich foods, although they should check with their doctor as to how much potassium they should eat:
"Our findings give women another reason to eat their fruits and vegetables. Fruits and vegetables are good sources of potassium, and potassium not only lowers postmenopausal women's risk of stroke, but also death."
To increase potassium intake, the AHA name the following foods among others as being high in potassium:
Previously, Medical News Today reported on a study that suggested a high-protein diet could lower the risk of stroke.