Fish Diet Aids Heart Health : Nutrition: Unlike past evidence, which was based on animal studies, new data comes from significant human tests.
Two significant studies--one recently published in the New England Journal of Medicine, the other presented before a meeting of scientists here--have demonstrated that eating two to three meals of fish per week can lower blood pressure in humans, a hypothesis that previously had been based solely on animal models and thus had been challenged.
Researchers now have evidence that people who consume large amounts of omega-3, a type of fatty acid primarily found in fish, have lower mortality rates from cardiovascular disease and experience fewer chronic or inflammatory illnesses such as rheumatoid arthritis, psoriasis and diabetes.
In the past, human trials had yielded conflicting results because, according to experts in the area, the body has a sophisticated regulatory mechanism that easily adapts to changes in blood pressure so that changes back to normal are stubbornly achieved.
But both findings, discussed at the II International Conference on the Health Effects of Omega-3 Polyunsaturated Fatty Acids in Seafoods, verify that fish oil does indeed lower blood pressure, the scientists reported. It should be noted that declines are observed as tiny increments compared to the results achieved with drug therapy, so fish oil intervention earlier in life is most effective.
In the first study, a population-based 10-week trial conducted by Dr. Kristian Bjerve and his colleagues in Norway, 156 men and women with previously untreated, stable mild hypertension were given either six grams of a highly concentrated form of fish oil or the same amount of corn oil. The average systolic blood pressure in the fish-oil group fell by 4.6 millimeters of mercury (mm Hg) and diastolic pressure by 3.0 mm Hg. There was no significant change in the corn-oil group.
Dietary supplementation with fish oil did not, however, change the mean blood pressure in those subjects who ate fish three or more times a week as part of their normal diet before the trial. This means that Americans could expect a greater decline in blood pressure since fish consumption in this country is low, Bjerve said.
In the other study, Professor David Mills of the University of Waterloo, Ontario, Canada, found that fish oil had a positive effect on the baroflex, a part of the brain that reacts to environmental stresses. This thermostat-like system responds to external stimuli such as stress or nervousness by causing either constriction or dilation of blood vessels, which, in turn, maintains arterial pressure.
The new evidence shows that fish oil’s positive effect on the brain could reduce one of the major causes of hypertension and stress and eventually reduce risk for cardiovascular disease.
“I’m looking at, in animal and human models, the prevention of the disorder rather than reversal once the disorder is there,” Mills said, “. . . especially in increased-risk populations (and) before the disease fully manifests itself. It appears that fish oil might have some usefulness.
“High blood pressure is symptomless and by the time (hypertensives) reach the clinical intervention stage, (they) already have a body change. The brain is like a thermostat, and it sets (itself) to a certain blood pressure level. It resists (change) no matter what you give. Giving fish oil before the arteries are plugged is like changing the oil (in your car) 20,000 miles earlier--before there’s been damage.”
Normal blood pressure for an adult is about 120/80 mm Hg, which denotes the force of the blood as it pushes against the arteries as blood is pumped from the heart. The reading, 120/80, is a ratio of systolic pressure over diastolic. (The word systole (systolic) describes blood as it is ejected from the heart to other parts of the body, whereas diastolic pressure is recorded when the valves relax and is called diastole. )
When the arteries are healthy, they are muscular and elastic and have an ability to stretch or contract when the heart pumps blood through them. The amount of stretching depends on the amount of force the blood exerts. Thus, if the passageways are narrowed, it’s harder for blood to pass through and blood pressure rises.
If blood pressure goes up, the heart works correspondingly harder. And if the pressure in a person’s arteries increases to 140/90 or higher and remains there, high blood pressure is diagnosed and the person is defined as hypertensive.
Blood pressure can be influenced in a number of ways. Inherited tendencies over which a person has little or no control include sex, age, race, family history and sensitivity to sodium. Plus, there are external factors that affect blood pressure. Some of these are alcohol consumption, the use of oral contraceptives, a sedentary lifestyle and environmental stress.
This is where fish meals have a role.
Adding a few fish meals a week to a balanced diet can help keep blood flowing through the narrow passageways to the heart, experts assert. It also reduces blood’s tendency to clot--a process that occurs naturally after an injury to arteries, such as cholesterol build-up--which leads to heart attack and stroke.
“We think this will encourage people to see the benefit of eating fish earlier in life,” said Dr. Kristian Bjerve of the department of clinical chemistry, University of Trondheim, Norway.
“Omega-3 probably is an unusual blood-pressure lowering agent since the corn oil groups don’t respond. In America, you might expect to have a larger than mean decline--on the average--because if they are eating fewer than two meals of fish a week you will probably get a beneficial effect.”
Bjerve explained that since those volunteers already eating fish had a reduced effect from fish oil supplementation, it could be significant in the United States, where fish consumption is low. Another important note, Bjerve said, is that his study achieved the benefit with fish meals--not just highly concentrated capsules.
“We (found) the same effect on blood pressure whether the fish oil was taken as meals or as capsules,” Bjerve said. “Omega-3 taken in during an ordinary diet has the same effect. Of course, you cannot (maintain) a high sodium intake or a high fat intake and expect omega-3 (capsules to lower blood pressure). You’ll need to reduce the salt and fat content of the diet. It’s important not to forget about the other risk factors. They are still important.”
