The link between good health and fish emerged in 1978, after a group of researchers from Denmark reported that the Inuit of northwest Greenland had one-tenth the death rate from heart attack as that of their Danish neighbors.
The scientists concluded that the Inuit diet, primarily made up of fish, seal and herring oil, protected them from high cholesterol, obesity, diabetes and heart disease.
Most societies do not have a diet like that, so the medical community took note in 1985 when Dutch scientists reported that only about 7 ounces of fish a week in a Western diet cut the coronary death rate by 50% in a group of 850 Dutch men who'd been tracked for 20 years.
Four years later, scientists in Wales reported that men who ate 6 to 12 ounces of fatty fish for two years after suffering a heart attack had a 29% lower mortality rate.
Fish eaters also have fewer strokes: In a study of 80,000 female nurses, eating fish twice a week reduced the incidence of stroke by about 50%. In a similar study of male physicians, only one fish meal per month cut the incidence of strokes by 44%.
A growing body of research suggests that the omega-3 fats that fish contains -- DHA and EPA -- seem to help the heart in several ways. Fish oils reduce elevated triglycerides, blood fats that are markers for heart disease risk, by as much as 30%. They inhibit development of plaques in arteries: One theory is that DHA and EPA may alter the way molecules adhere to the vascular walls. And higher fish consumption seems to improve blood vessel elasticity, thereby helping to reduce blood pressure.
The most consistently reported benefit of omega-3s appears to be a stabilizing effect on the heart muscle itself, reducing the risk of heart arrhythmias, the most common cause of sudden cardiac death.
"The amount of omega 3s we need for protection of cardiac arrhythmias is small, roughly what we get in two servings of fish a week," says Dr. Walter Willett, professor of epidemiology and nutrition at the Harvard School of Public Health. "It's remarkable that there is so much benefit for such a modest amount."
New research indicates that fish may feed the brain as well as the heart. In one study, older individuals who ate fish once a week or more had a 60% lower risk of Alzheimer's disease, compared with those who avoided seafood. Likewise, elderly Chicago residents who ate fish twice a week slowed their rate of cognitive decline by 13% on standardized tests.
This link makes good sense, says Martha Clare Morris, the lead researcher on these studies on fish and cognition, and an associate professor of preventive medicine at the Rush University Medical Center in Chicago.
Omega-3s are vital to the overall function of nerve cells in the brain and for keeping the nerve cells healthy, she says. "DHA is one of the primary lipids in the human brain, and the primary lipid in areas of the brain that work the hardest." As we age, we lose DHA, so replacing it with food may be helpful.
Indeed, DHA has been shown to have a positive effect on the aging brain in animals.
The list of possible omega-3 benefits is growing longer. Fish oil seems to elevate mood and improve depression: In a group of Finnish women, the risk of developing depression was 2.6 times greater in women who rarely ate fish compared with the regular fish eaters. People who suffer from depression and schizophrenia improve when omega-3s are added to their medications.
Fish may also prevent a common eye disease associated with aging. The journal Archives of Ophthalmology recently reported a 40% reduction in macular degeneration, the leading cause of blindness in people older than 49, among those who ate fish once a week.
Studies also suggest that eating fish slows the progression of prostate cancer, the No. 1 cancer in men, and reduces the risk of colon cancer, the nation's second largest cancer killer.