By Ed Edelson
MONDAY, July 7 (HealthDay News) -- High intake of the omega-3 fatty acids in oily fish and vegetable cooking oils appear to help prevent heart attacks, while the omega-6 fatty acids in vegetables and nuts help keep blood pressure low, two international research teams report.
A study in Costa Rica found that high intake of omega-3 fatty acids reduced the risk of heart attack by 59 percent, said a report published in the July 8 online issue of Circulation.
In the Costa Rican study, "we compared those subjects who had heart attacks with those who did not have heart attacks," said study author Hannia Campos, a senior lecturer in nutrition at the Harvard School of Public Health. They had participants fill out food questionnaires and also analyzed body fat samples to determine levels of alpha-linolenic acid, a major omega-3 fatty acid.
A number of other studies have shown that high intake of omega-3 fatty acids is associated with lower risk of death from cardiovascular disease. This is the first study to look at its association with heart attack risk, Campos said.
"We found that the relationship is not completely linear," she said. "It plateaued after a certain level of intake. After that, higher levels do not mean increased protection."
The protective level turned out to be surprising low -- the amount in two teaspoons of soybean oil or canola oil, half a teaspoon of flaxseed oil or six to 10 walnut halves.
That protective effect could be detected, because the people in the Costa Rican study have a low level of omega-3 fatty acids in their diet, Campos said. "Their overall intake of fish is very low, much lower than in the United States, and the fish they eat are tropical, which are not as fatty as cold-water species," she said.
The high blood pressure study, reported in the July 8 online issue of Hypertension, looked at 4,680 men and women aged 40 to 59 from China, Japan, the United States and the United Kingdom. It found a significant relationship between intake of linoleic acid, an omega-6 fatty acid found in vegetables, and lower blood pressure.
The report is the latest in a series of studies designed to describe all the factors contributing to high blood pressure, said Dr. Jeremiah Stamler, a professor of preventive medicine emeritus at Northwestern Feinberg School of Medicine.
"For diet and serum cholesterol, most of the answers came in the 1960s," Stamler said. "The data on diet and blood pressure have come much more slowly."
Previous reports have shown that higher intake of calcium, magnesium and phosphorus are associated with lower blood pressure, Stamler said. Iron from vegetables -- but not meat -- also is associated with lower blood pressure, he said. "An array of macro- and micronutrients influence blood pressure in a variety of ways," Stamler said.
The latest study indicates that raising linoleic acid intake by 9 grams a day reduces systolic blood pressure (the higher of the 120/80 reading) by about 1.4 points, and diastolic pressure by about 1 point. That small reduction can have a large effect in a big population, the researchers said, with a 2-point reduction reducing coronary heart disease by 4 percent.
"The message of this study is to eat more fruit and more vegetables, more beans, less red meat and less fats," Stamler said. "Fats should be mainly selected to be unsaturated. Vegetable oils should be used but in moderation."
A guide to omega-3 and omega-6 fatty acids is offered by the Vegan Society.