Four studies published this month report benefits for fish and omega-3 fatty acid consumption with regards to heart disease and Alzheimer disease. These studies are of particular note for people with diabetes because they are at an increased risk of developing both of these conditions.
Heart health. One review of multiple studies, published in the October 18 issue of The Journal of the American Medical Association, found that 1–2 servings per week of fish and shellfish, especially species high in the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), reduced risk of death from heart disease by 36% and overall risk of death by 17%. The researchers concluded that these potential benefits far outweighed any health risks posed by methylmercury, dioxin, and polychlorinated biphenyl (PCB) contamination of fish. Levels of these contaminants in store-bought fish, the researchers said, were low.
The report specified that women who are pregnant or nursing or could become pregnant should avoid the four fish species that are highest in methylmercury (which can lead to developmental problems in newborns). These species are king mackerel, shark, swordfish, and golden bass (also known as tilefish). These women should also consume less than six ounces per week of albacore (or “white”) tuna, which can also be high in methylmercury. The researchers recommend that these women consume a variety of all other species of fish, however, since there is evidence that higher fish intake and DHA levels in mothers are associated with improved infant brain development.
A second report released at the same time by the Institute of Medicine (IOM), a subsidiary of the National Academy of Sciences, was not quite as optimistic but concluded that fish and shellfish intake may reduce people’s overall risk of heart disease. This report, also based on a review of several studies, emphasized that it is not clear whether seafood is beneficial to heart health because it replaces fatty cuts of meat (which are sources of saturated fat and cholesterol) in people’s diets or because the omega-3 fatty acids found in seafood have a protective effect on the heart. It did acknowledge that maternal consumption of omega-3 fatty acids from seafood have been shown to be beneficial to infants’ vision and cognitive development. Both studies emphasized that fatty, cold-water fish—such as salmon, mackerel, sardines, anchovies, and herring—are the richest sources of omega-3 fatty acids.
Alzheimer disease. An additional two studies, both published in the October issue of the journal Archives of Neurology, showed possible benefits for fish and omega-3 fatty acid consumption in preventing or slowing the progression of Alzheimer disease. The first study showed that people who eat a “Mediterranean” diet—which includes fish among several other components—have a lower risk of developing Alzheimer disease. In this study, researchers collected data on almost 2,000 people with an average age of 76, 194 of whom had developed Alzheimer disease. The researchers analyzed the study participants’ diets over the previous year and discovered that the more closely a participant had followed a Mediterranean diet (which is rich in fruits, vegetables, olive oil, legumes, cereals, and fish, low in meat and dairy, and includes mild to moderate alcohol consumption), the lower his risk of developing Alzheimer disease.
The second study showed that omega-3 fatty acid supplements slowed cognitive decline in a small group of people who already had very mild Alzheimer disease. The study examined 174 people with Alzheimer disease who were given either a daily omega-3 supplement containing 1.7 grams of DHA and 0.6 grams of EPA or a placebo. The researchers found no significant difference in cognitive decline between the two groups after six months. However, in a subgroup of 32 participants who had very mild cognitive impairment at the beginning of the study, those who received the omega-3 supplements experienced less cognitive decline than those who received placebos. What’s more, when the participants in the placebo group were switched to an omega-3 supplement, their cognitive decline decreased after an additional six months.
While the reason the supplements were helpful only to people with very mild Alzheimer disease is not clear, the researchers theorized that the anti-inflammatory effect of omega-3 fatty acids may only play a beneficial role in the disease’s early stages.
Experts have concluded that diet probably plays a role in the development of Alzheimer disease, and that steps taken to reduce cardiovascular risk may also help reduce people’s risk of Alzheimer disease.