Fish consumption and cognitive function among older people in the UK: baseline data from the OPAL study

Observational epidemiological data suggest that habitual consumption in later life of oily fish, rich in n-3 long-chain polyunsaturated fatty acids (n-3 LCPs), is associated with better cognitive function, slower rates of cognitive decline and a lower risk of dementia. In this paper we present data on baseline fish consumption and cognitive function in cognitively healthy older people randomised onto the Older People And n- 3 Long-chain polyunsaturated fatty acid (OPAL) study.

In total, 867 older people were recruited to join the OPAL study from 20 general practices in England and Wales. Participants were aged 70-79 years at baseline were free of dementia and diabetes, had a Mini-Mental State Examination score of 24 or greater and did not report daily fish oil supplement consumption. Self-reported habitual fish consumption was assessed at baseline via questions on frequency and type of fish consumption. Cognitive function at baseline was assessed via validated cognitive tests assessing memory, executive function, psychomotor speed and attention, including the Californian Verbal Learning Test (CVLT), the primary outcome of the OPAL study. Reported age at leaving full time education was recorded as a measure of educational achievement and psychological health was measured using the GHQ-30 questionnaire.

Unadjusted analysis revealed significant positive associations between reported fish consumption and the CVLT scores with a mean increase of approximately 0.24 words remembered for each increase in level of reported fish consumption. These associations were noticeably attenuated on adjustment for age, gender and reported age at leaving full-time education and did not remain significant on further adjustment for GHQ-30 score. Similar associations were also observed between fish consumption and the global cognitive z-score, memory score, executive function score and delay scores in unadjusted analysis with the associations again attenuated on adjustment.

Baseline data from participants randomised into the OPAL study provide support for the hypothesis that higher fish consumption is associated with better cognitive function in later life. However, although in the main associations remain after adjusting for education and psychological health, the data do not allow us to rule out the possibility of residual confounding e.g. from socioeconomic status or other health behaviours. Evidence is needed from randomised clinical trials to clarify the role of n-3 LCPs in cognitive health in later life in the normal older person population.