Fatty fish is high in the long chain fatty acids docosahexanoic acid (DHA, C22:6 (n-3)) and eicosapentanoic acid (EPA, C20:5 (n-3)) that have been shown to have health benefits. In particular, DHA and EPA are able to inhibit inflammation because they accumulate in cell membranes and are metabolised to the anti-inflammatory series 3 eicosanoids. In contrast, meat contains arachidonic acid, which is incorporated into cell membranes and converted to the pro-inflammatory series 2 eicosanoids. The amount of meat and fatty fish in the diet therefore has an influence on the degree of inflammation, and chronic systemic inflammation is thought to contribute to the development of dementia. Fatty fish may offer protection from dementia because DHA is preferentially sequestered by the brain from plasma where it is thought to decrease tissue inflammation, increase neuronal membrane fluidity, improve neurotransmitter efficiency and possibly allow neurogenesis.
Research1 has investigated the association between fish and meat consumption with dementia in low and middle income countries using a cross-sectional survey. Residents over 65 years in China, India, Cuba, the Dominican Republic, Venezuela, Mexico and Peru (14,960 residents) were interviewed face to face and filled in a questionnaire in order to ascertain an understanding of their sociodemographic characteristics, health status, health behaviours and risk factor exposure. The subjects were also given neurological and physical examinations. The results showed that there were 1340 dementia cases in the whole sample and the prevalence varied from between 6.3% to 11.7% from country to country. Hypertension and cardiovascular disease tended to be more common in the more developed Latin American Countries, particularly Cuba, which supports the contention that cardiovascular disease is a lifestyle disease associated with developed countries.
Fish consumption was highest in Venezuela and China and was lowest in the Dominican Republic and India. Meat consumption was lowest in Venezuela and highest in the Dominican Republic, China and Cuba. Consumption of both meat and fish tended to be lower in older subjects but this was not statistically significant in all countries. After statistical analysis, there was a dose-dependent inverse association between fish consumption and dementia that was present in all countries except India, but this association was attenuated somewhat by adjustment for variables such as age, sex and education levels. There was also a dose-dependent positive association between meat consumption and dementia but the pattern was not consistent across all countries. These results support previous research that shows a protective effect of fatty fish against dementia, and provide evidence that dietary factors contribute to the development of cognitive decline.
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