October 17, 2005
Eating fish at least once a week may slow memory loss in seniors, a new study reports. The findings, published in the medical journal Archives of Neurology from the American Medical Association, add to a growing body of evidence that fish, particularly those rich in "good" fats called "omega-3s," may benefit both the heart and brain.
Researchers at Rush University Medical Center in Chicago found that men and women aged 65 and up who ate fish one or more times a week had, on average, a 10 percent slower rate of cognitive decline as they aged compared to those who rarely ate fish. Over time, the benefits added up to the equivalent of being three to four years younger mentally, the researchers estimate.
"Dietary intake of fish was inversely associated with cognitive decline over six years in this older, biracial community study," the researchers report. "The rate of decline was reduced by 10 percent to 13 percent per year among persons who consumed one or more fish meals per week compared with those with less than weekly consumption. The rate reduction is the equivalent of being three to four years younger in age."
"This study suggests that eating one or more fish meals per week may protect against cognitive decline associated with older age," the authors conclude. "More precise studies of the different dietary constituents of fish should help to understand the nature of the association."
The "Good" Fats in Fish
Fish contain fats called omega-3s that may have benefits for the heart and blood vessels, helping to lower the risk of heart attacks and strokes. Omega-3s have also been shown to be essential for brain development and healthy brain function. Research is ongoing to determine whether fish oils may help to ward off Alzheimer's disease and other forms of dementia as well.
One form of omega-3 called DHA, or docosahexaenoic acid, may have particular benefits for the brain. Earlier this year, researchers at the University of California, Los Angeles reported that mice fed fish-oil supplements containing a form of omega-3 called DHA had less buildup of amyloid in the brain. (See the article, "Fish Oil Shows Promise in Alzheimer's Fight") An excess of this sticky protein is thought to form plaques and patches in the brain and damage the memory of those with Alzheimer's disease.
Population studies suggest that men and women who eat lots of fish may be less likely to develop dementia as they age. Scientists have discovered that the brains of persons with Alzheimer's disease also tend to be low in DHA. Nutritionists say that many Americans do not get enough omega-3s in their daily diets.
What the Study Showed
The current study was conducted in more than 6,000 older men and women, both whites and African-Americans, living in the Chicago area. They were first interviewed between 1993 and 1997, then given regular follow-up exams after three years and again three years after that. They were given memory tests as well as dietary questionnaires about how often they ate 139 different foods, including fish. They were also asked about their daily activities, how often they exercised, how much alcohol they drank, and any medical problems.
After six years, the researchers found that those who ate one fish meal a week had a 10 percent slower rate of cognitive decline compared to those who ate fish less often. Those seniors who ate fish two or more times a week had a 13 percent lower rate of mental decline. The investigators examined whether other "heart-healthy" foods may have accounted for the association of cognitive decline and fish consumption, but the rate differences did not change after adjusting for consumption of such foods as fruits and vegetables.
Oily, coldwater fish, such as salmon, halibut, mackerel, sardines, and herring, are particularly rich in DHA and other omega-3s. DHA/omega-3 dietary supplements are also widely available in pharmacies and health-food stores. Other foods high in these "good" fats include almonds, walnuts and many other types of nuts, as well as canola, walnut, soybean and flaxseed oils. Because many of these foods are a rich source of calories, however, it is best to eat them in place of, rather than in addition to, other foods.
More research is needed to help determine whether fish or fish oil really help keep the mind sharp. In addition, fish oils are now being tested in clinical trials in people in the early stages of Alzheimer's to see if they help slow the disease, but results will likely not be available for several years. In the meantime, it may be a good idea to "eat your fish," just as your mother advised.
Martha Clare Morris; Denis A. Evans; Christine C. Tangney; et al: "Fish Consumption and Cognitive Decline With Age in a Large Community Study." Archives of Neurology, early online release (doi:10.1001/archneur.62.12.noc50161).