The American Alzheimer's Association recommend a diet rich in oily fish due to the benefits associated with omega-3 fatty acids. Consuming fish only once a week will significantly reduce the risk of developing Alzheimer's disease.
Dementias now affect nearly half of the western population aged over 80, with Alzheimer’s disease (AD) being a leading and growing cause. There is no cure and its causes are not well understood. Researchers in at the University of Guelph, Canada, have found only low levels of long-chain fatty acids, notably DHA, in people suffering from dementias, including Alzheimer’s. The study looked at 84 people aged 80 and over. Nineteen were diagnosed as having AD, 10 had non-AD dementia, 36 did not have dementia but were cognitively impaired and 19 had normal cognitive functioning. Levels of EPA and DHA were significantly higher in the final group of 19 than in those with dementias or cognitive impairment. The Guelph researchers concluded that efforts should be made to increase the intake of fish or fish oils in the population in general and in the elderly in particular.
A prospective study in the US followed 815 people aged over 65 from 1993 to 2000. Initially none had Alzheimer’s disease. During the study period 131 developed the disease. When incidence was compared with diet it was seen that those who consumed fish at least once per week had 60% less risk of developing Alzheimer’s disease than those who consumed it less often or not al all.
Three European studies reinforce these observations. A French team tracked a cohort of 1,674 people aged 68 to 75 for seven years. Participants who ate fish or seafood at least once a week had a 44% lower risk of being diagnosed with dementia than those who ate it less often, and a 31% lower risk of being diagnosed with Alzheimer’s disease.
The middle aged can also benefit. In the Netherlands, data was extracted from a cross-sectional population-based study among 1,613 people ranging from 45 to 70 years of age. The authors concluded that consumption of fatty fish and omega-3 fatty acids was associated with a reduced risk of impaired cognitive function, whereas consumption of cholesterol and saturated fat was associated with an increased risk.
Looking for more direct evidence, another team in France used fatty acid levels in red blood cell membranes as a surrogate means of assessing levels in the brain of 246 subjects aged 63–74. These were compared with cognitive status over a four-year period (1995–2000). Those whose cognition declined had significantly lower levels of DHA and EPA and significantly higher levels of omega-6 fatty acids.
The accumulating evidence has led, for example, to the American Alzheimer’s Association including the following in its dietary recommendations, “Eat more oily fish such as salmon, halibut, trout and tuna. They are rich in beneficial omega-3 fatty acids.”