January 5, 2010
There's more good news on the fish front: A large study conducted in developing countries found that a diet rich in fish may lower the risk of Alzheimer's disease and other forms of dementia. And the more fish people ate, the less likely they were to develop the serious memory loss of dementia. The study adds to a growing body of evidence that a fish-rich diet may offer benefits for brain health.
Past research has suggested that eating fish may help to ward off dementia, but most of those studies were carried out in the United States other developed countries. Studies of people living in Italy, France and Spain who eat a traditional Mediterranean diet rich in fish as well as fruits and vegetables, for example, have shown that the diet may have brain-protective effects.
Dietary studies can be unreliable and difficult to analyze, because they typically rely on people reporting their daily food intake over many years and generally don't take into consideration many other dietary and life-style variables that may affect health. But review of large populations can be helpful for suggesting possible associations between diet and diseases like Alzheimer's.
The study, a survey of nearly 15,000 men and women ages 65 and older, was conducted in a broad swath of developing countries across Asia, Latin American and the Caribbean. Among adults living in China, India, Cuba, Venezuela, Mexico, Peru and the Dominican Republic, those who ate fish almost every day were almost 20 percent less likely to develop dementia than those who ate fish a few days a week. Those who ate fish a few times a week were, in turn, were 20 percent less likely to develop dementia than those who rarely or never ate fish.
The findings are consistent with earlier reports that suggest that eating oily fish like tuna, salmon, mackerel, sardines and anchovies may help to keep the mind and memory sharp. Eating fish may also help to ease the agitation and depression of Alzheimer's, other research shows.
Fish oils contain omega-3 fatty acids like EPA and DHA, which are known to be good for cardiovascular health. They also may help protect the brain against strokes and memory loss. DHA, or docosahexaenoic acid, and EPA, or eicosapentaenoic acid, are both thought to have disease-fighting properties.
Researchers speculate that the DHA and EPA in omega-3s may quell inflammation, which is emerging as a possible underlying cause of heart disease and other ills, including Alzheimer's disease. Omega-3s may also help to block the formation of the beta-amyloid plaques that can clog the brains of those with Alzheimer's disease.
In addition to fish, DHA and omega-3 dietary supplement pills 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.
Still, more research is needed to help determine whether fish or fish oil supplements really help keep the mind sharp. Some concern has also been raised about mercury and other nerve-damaging toxins that tend to collect in certain species of fish, though supplements tend to be low in toxins. Scientists continue to study the effects of diet on brain health. In the meantime, a varied diet that includes fish is probably a good idea.
Emiliano Albanese, Alan D Dangour, Ricardo Uauy, et al: "Dietary fish and meat intake and dementia in Latin America, China, and India: a 10/66 Dementia Research Group population-based study." American Journal of Clinical Nutrition, Volume 90, pages 392-400, first published online June 24, 2009; doi:10.3945/ajcn.2009.27580