Evidence Finally Links Dietary Fat, Sodium to Stroke
Public health guidelines may change.
Internal Medicine News
March 1, 2005

By Mitchel L. Zoler, Philadelphia Bureau

New Orleans -- For the first time, physicians have evidence independently linking high dietary levels of fat and sodium to an increased risk of ischemic stroke, based on findings from an epidemiologic study in New York.

Experts who heard these findings at the 30th International Stroke Conference hailed them as a key step for changing U.S. public health guidelines.

Until now, "there has not been evidence of a strong association" between dietary fat and sodium and stroke, said Lawrence Brass, M.D., professor of neurology, epidemiology and public health at Yale University, New Haven.

"These new data will allow us to make a stronger statement," added Dr. Brass, a member of the American Stroke Association's committee that writes guidelines for the primary prevention of stroke. "I can't speak for the whole committee, but this is the type of information that may prompt us to [look again at] the guidelines," he said.

A link between fat and sodium and stroke "may sound like common sense, but guidelines are based on available scientific data. Without the data we can't include them," said Ralph Sacco, M.D., professor of neurology and epidemiology at Columbia University in New York and the senior investigator for both of the new studies.

Both studies used data collected in the Northern Manhattan Study of 3,298 people living in northern Manhattan in 1993. The subjects were thoroughly assessed at baseline, and 3,183 answered a food frequency questionnaire that was used to calculate dietary fat and sodium intake. At entry, this group had a mean age of 70 years; 63 percent were women, 21 percent were white, 24 percent were African American, and 52 percent were Hispanic. They were followed for an average of 5.5 years, during which 142 had an ischemic stroke.

The analysis of the link between stroke incidence and dietary fat assessed fat intake both as a continuous variable, with 65 g / day as the dividing line between a low- and high-fat diet. The National Cholesterol Education Program recommends that fat should be about 30 percent of total caloric intake; a person who eats 2,000 calories per day should have a daily fat intake of no more than 65 g. About 36 percent of people in the study reported eating more than 65 g of fat daily.

In the dichotomous analysis, the ischemic stroke incidence was 60 percent higher in people who consumed more than 65 g of fat daily, compared with those who at 65 g or less, reported Halina White, a researcher at Columbia. This analysis controlled for a variety of demographic, clinical, and dietary variables. When adjusted for total caloric intake, the increased risk of stroke linked with a high-fat diet rose to 90 percent.

"These are reasonable hazard rates that are close to the increased risk for stroke in patients with hypertension," said Dr. Sacco, who is also director of stroke and clinical care at Columbia. He speculated that atherosclerosis may be the mechanistic link between high dietary fat and stroke. High-fat diets usually lead to increased serum levels of total cholesterol and LDL cholesterol, he said.

The sodium analysis divided participants into three groups with mean daily sodium intakes of 4 g or more, 2.4 g or less, or between 2.4 g and 4 g. In an analysis that controlled for potential confounding variables including hypertension, people who ate 4 g or more per day had an 84 percent higher risk of ischemic stroke than people who consumed 2.4 g or less per day, reported Armistead D. Williams III, M.D., a neurologist at Columbia.

People who ate between 2.4 and 4 g per day had a slightly but not significantly increased risk of stroke, compared with those with the lowest intake. Because the analysis controlled for differences in blood pressure, it's possible that some other, unknown biological mechanism explains the link between dietary sodium and stroke risk. But blood pressure could still play a role, Dr. Sacco said at the meeting, sponsored by the American Stroke Association.

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