SAN DIEGO — An extra banana or a helping of fresh broccoli a day could provide important protection against death from stroke by increasing the body's potassium, a study by the University of California, San Diego, School of Medicine indicates.
The findings show that a diet high in potassium can lower the risk of stroke as much as 40% regardless of other risk factors, such as age, weight, smoking habits, cholesterol levels or blood pressure, Dr. Elizabeth Barrett-Connor said here Wednesday.
But she cautioned that individuals should not take potassium supplements in a pill, or in any other non-food form. And she said a high-potassium diet per se cannot be categorically recommended as a sure way to prevent stroke until other studies confirm this finding.
"A supplement could possibly interfere with something else (biochemically in the body) and I don't think people should be fooling around with potassium that way," Barrett-Connor said. She also recommended that people with kidney or hypertension problems consult their doctors before changing diets.
"But in the context of fresh fruits and vegetables being helpful in possibly preventing cardiovascular disease and some forms of cancer as well, an extra helping (of potassium-rich foods) is in no way harmful to the general public and could be quite beneficial," she said.
Other foods high in potassium include avocado, cantaloupe, dates, prunes, raisin, potatoes with skins, Brussels sprouts, cauliflower and mushrooms.
Barrett-Connor and co-author Kay-Tee Khaw, an epidemiologist at both UCSD and Cambridge University School of Medicine in England, published their results in this week's New England Journal of Medicine.
They based their findings on data from an ongoing heart and chronic diseases study at UCSD, begun in 1972, involving more than 5,000 residents of suburban Rancho Bernardo. The potassium data came from 859 white men and women between the ages of 50 and 79.
In 1975, the participants were asked detailed questions by dietitians about their food consumption for a 24-hour period, including the size of portions and whether or not the diet was representative of their daily intake. The information was coded for trace minerals, vitamins, and other nutrients. Since then, the participants have been followed closely.
It turned out that the 24 who died had significantly lower levels of potassium in their diet than survivors and those who died from other causes, Barrett-Connor said.
Small Amount Needed
The researchers found that the stroke risk in men whose daily potassium intake was below 59 millimoles, a very small amount, was about three times that of men with higher consumption. (One serving of raw fruit or vegetables contains about 10 millimoles of potassium.) For women, the risk for those who took in less than 49 millimoles each day was five times that of women who ate more.
The researchers calculated that a 10-millimole increase in daily potassium intake was associated with a 40% reduction in risk. Typically, Americans consume between 60 and 70 millimoles of potassium each day.
The reason for potassium having an apparent effect in preventing stroke is not clear from the type of study done, Barrett-Connor said. It has been known from clinical work previously published by Khaw that potassium lowers the blood pressure in individuals.
But Barrett-Connor said that any stroke prevention action by potassium is independent of the effect that potassium has on lowering blood pressure. Those with high dietary potassium levels had a lower risk of stroke regardless of their blood pressure. That relationship held true even for people who smoked, who were older, who had higher blood cholesterol levels or who had any other factor associated with higher stroke risk.
After heart attacks and cancer, strokes are the third-leading cause of death in this country. About 400,000 Americans a year experience strokes, which are caused by blood flow being cut off to the brain because of blocked or burst blood vessels or arteries, and about 155,000 of them die.
Stroke deaths have been declining since the late 1940s, when consumption of fresh fruits and vegetables began to increase--a phenomenon that may be explained in part by her data. "This may be part of the missing link," Barrett-Connor said.