"A large percentage of people aged between 20 and 60 have a rise in blood pressure and by middle age many have high pressure, " said a professor of preventive medicine who took part in the study.
Dr. Jeremiah Stamler, of Northwestern University in Chicago, went on, "We're looking at dietary factors that may help prevent that rise, and omega-3 fatty acids are a small, but important piece of the action." The study looked at diet and its relation to blood pressure in 4,680 men and women aged 40 to 59 and living in Britain, Japan, China and the United States.
They provided details of diet and alcohol consumption, gave urine samples and had their blood pressure measured twice at each of four study visits.
Researchers adjusted for 17 variables known to influence blood pressure, such as age, gender, weight, salt intake and exercise.
The people with diets rich in omega-3 fatty acids had slightly lower blood pressure on average than people who ate food with less of the nutrient, the researchers reported in the American Heart Association journal Circulation.
Dr. Hirotsugu Ueshima of Shiga University in Otsu, Japan, said, "With blood pressure, every millimeter counts. The effect of each nutrient is apparently small but independent, so together they can add up to a substantial impact on blood pressure.
"If you can reduce blood pressure a few millimeters then you've made a big difference." His advice includes eating less salt, losing a few pounds, avoiding heavy drinking, eating more vegetables, whole grains and fruits -- for their fiber, minerals, vegetable protein and other nutrients -- and getting more omega-3 fatty acids.
However, when it comes to omega-3 fatty acids, not all fish or nuts are equal. Fatty fish such as trout, salmon and mackerel are rich in this crucial group of nutrients.
Walnuts, flaxseed and canola oil are also good for omega-3 fatty acids.
People who got their omega-3s from these sources enjoyed just as much benefit as those deriving them by eating fish, the study found.
Omega-3 fatty acid intake has also been linked to better brain development and a lower overall risk of cancer and heart disease.
A diet rich in oily fish can also dramatically reduce the chances of kidney cancer in women, according to research in Sweden.
Eating one portion of fish such as salmon, mackerel, herring or sardines slashed the risk by more than 70%, the study found.
Women with renal cell carcinoma were less likely to eat oily fish regularly, said scientists.
From the June 18, 2007, Prepared Foods e-Flash
