The results of a large urban multiethnic study show that high fat and high sodium diets are both risk factors for stroke, investigators with the Northern Manhattan Study (NOMAS) reported here Thursday.

NOMAS is an ongoing epidemiological study being conducted at Columbia University Medical School in New York. Investigators administered dietary questionnaires to 3,183 area residents. The average age of the subjects was 70 years; 21 percent were white, 24 percent black and 52 percent Hispanic. During 5.5 years of follow-up, 142 strokes have occurred.

The participants were divided into four subgroups according to the level of fat in their diet. These amounts were compared dietary fat levels recommended by the American Heart Association, which are 65 grams of fat per day - based on a 2,000 calorie diet with 30 percent of calories derived from fat.

The subjects who ate the most fat each day had a 64 percent greater chance of having a stroke compared with those who ate the lowest levels, postgraduate research fellow Halina White reported at the American Stroke Association’s International Stroke Conference 2005.

This figure was obtained after other factors that affect stroke risk were considered including age, gender, education level, race, ethnicity, high blood pressure, heart disease, diabetes, moderate alcohol consumption, smoking, body mass index and physical activity. She said subjects in the lowest dietary fat group consumed about 24 grams per day, while those in the highest group consumed more than 115 grams per day.

“Fat, particularly saturated fat…has an almost hormonal effect on the blood, causing the release of cholesterol, among other effects,” White told Reuters Health. “Polyunsaturated fats have the opposite effect.”

Neurology resident Armistead D. Williams, III, also presented data from NOMAS showing that a high sodium intake increases stroke risk. The same group of subjects was divided into four subgroups according to daily sodium consumption - more than 4 grams, 3 to 4 grams, 2.4 to 3 grams, and less than 2.4 grams.

About one fifth of the study group consumed more than 4 grams of sodium a day, Williams noted.

The investigators used 2.4 grams as a reference level because an intake of 2.4 grams sodium daily or less meets the American Heart Association recommendation.

Consumption of more than 4 grams sodium a day increased stroke risk by 90 percent compared with the reference group, Williams reported. This was consistent regardless of whether or not the subject had high blood pressure, he added.

NOMAS lead investigator Dr. Ralph L. Sacco noted that “we can’t exclude the blood pressure effect, but it is small.”

Williams told AMN Health that it is possible that the sodium is increasing the rigidity of the artery walls. “That’s one of the things we’re going to look at when we get back to New York.”