(20-10-09) Multi-Country Study Confirms Link Between Fish Consumption and Dementia Risk

At present there are no effective measures to prevent dementia and few ways to tell whether an individual will develop this chronic progressive condition.
Certain behaviors, such as adherence to a Mediterranean diet, higher physical activity, customary fish intake and control of other chronic conditions (heart disease, hypertension, hyperlipidemia, smoking, obesity), may reduce the chance of becoming demented, but the evidence is far from convincing. Control of
vascular factors and positive psychosocial activities are thought to have
beneficial effects, but these may be insufficient.

The regular consumption of fatty fish before the onset of symptoms, has been reported to reduce the risk of dementia and Alzheimer?s disease in several epidemiological studies, but the findings are inconsistent. Some clinical trials with long-chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFAs), the
likely active components in fish, have shown slower rates of cognitive decline in individuals with early signs of dementia, but not all studies have observed such effects. Thus, it is thought that the consumption of fish or n-3 LC-PUFAs
needs to begin early in adulthood if it is to affect the chance of developing dementia.

Most research on dementia and Alzheimer?s disease has been carried out in developed countries, whereas two-thirds of people with dementia live in low- and moderate-income countries. To address the needs of people in these countries and to learn more about the genetic and environmental causes of dementia, an international research group, ?10/66,? was formed as part of Alzheimer?s Disease International to conduct population-based research on dementia. This report of cross-sectional observations describes the findings
from 7 countries?Peru, Mexico, China, India, Cuba, Dominican Republic and Venezuela?on the consumption of meat and fish and the prevalence of dementia in adults 65 years of age or more. There were 14,960 participants from rural and urban areas.

A standardized study protocol was used in all countries. Interviewers were trained in the implementation of the assessment questionnaires. Dietary habits on weekly fish and meat intakes were assessed in face-to-face interviews and dementia diagnosed according to an algorithm developed by the study team applied to 3 mental health assessments as described previously.

The prevalence of dementia varied from 6.3% in China to 11.7% in the
Dominican Republic and has been reported previously. Not surprisingly, fish and meat intakes varied considerably among countries with the lowest frequency of fish consumption (never) and the most frequent fish consumption reported for Venezuela and China, respectively. These contrasting observations for the same
countries likely reflect differences in rural versus urban sampling areas.
Except for Venezuela, more than half the respondents in each country reported eating fish some days a week.

With the exception of India, fish consumption was inversely associated with the prevalence of dementia (Table). The investigators calculated prevalence ratios for the association between fish or meat consumption and dementia using Poisson regression models adjusted for household clustering, dietary intakes, age, sex, family history of dementia, education, number of assets, servings of
fruit and vegetables per week and alcohol consumption. The analysis also controlled for depressive symptoms, stroke, diabetes, coronary heart disease, smoking and meat or fish consumption. When all the results were pooled, the overall prevalence ratio was 0.8 (95% CI, 0.7 to 0.9). China was the only country where fish intake was significantly associated with less dementia and
India the only country where the association was positive. Fish consumption was not related to the severity of dementia in any country.

When the same analysis was applied to the association between dementia and meat consumption, a significant positive association was observed for the pooled data and individually for Peru and Cuba. In these latter countries, about 38% of participants said they ate meat every day or most days. In the sample overall, those reporting meat consumption every day or most days ranged
from 7% in India to 55% in the Dominican Republic. The pooled effect of eating meat for all countries was 1.2 (95% CI, 1.1-1.3). Interestingly, in Cuba, higher meat consumption was associated with more severe dementia.

This large, multi-country cross-sectional study confirms several previous reports in population subgroups that fish consumption is associated with a lower chance of dementia, though inconsistencies in individual countries and
the literature suggest that this relationship may be confounded by other
factors, methodological differences and the difficulties in measuring food intakes. The study suggests that the link between fish consumption and dementia in developed countries generally, though not always, applies in lower income countries too.

Albanese E, Dangour AD, Uauy R, Acosta D, Guerra M, Guerra SS, Huang Y, Jacob KS, de Rodriguez JL, Noriega LH, Salas A, Sosa AL, Sousa RM, Williams J, Ferri CP, Prince MJ. Dietary fish and meat intake and dementia in Latin America, China, and India: a 10/66 Dementia Research Group population-based study.

Source: Am J Clin Nutr 2009;90:392-400.

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