DHA and cognitive function in the elderly: A systematic review of the literature

Abstract

Docosahexaenoic acid (DHA), an omega-3 fatty acid, has been shown to be critically important for human brain development in utero and throughout infancy. Some evidence also suggests a beneficial effect of dietary fish consumption and omega-3 fatty acids in prevention of age-related cognitive deterioration. However, the evidence has not been systematically assembled and reviewed to establish the role of DHA in age-related cognitive deterioration. Perform a systematic review of published literature to identify the evidence relating DHA to prevention or treatment of dementia and cognitive decline in the elderly. We performed a systematic review of studies published from January1990 through September 2004 that assessed effects of omega-3 fatty acids on dementia-related outcomes in humans and established animal models of Alzheimer Disease. The systematic review identified 14 human studies and 5 Alzheimer animal model studies that assessed DHA levels in body tissues. All five Alzheimer model studies reported that mice on low DHA diets displayed learning impairment and DHA supplementation decreased or ameliorated learning impairment. Each of four pilot interventional studies found that DHA (0.6 to 1.4 g/d) improved cognitive functioning in healthy elderly subjects and/or elderly with dementia. Each of three prospective observational cohort studies that assessed DHA levels in blood, involving 1462 healthy elderly followed for 4 to 10 years, found that DHA levels per se were inversely associated with incident dementia/cognitive impairment. Four of six case-control and cross-sectional studies that measured plasma lipids and two of three similar studies that measured erythrocyte membrane fatty acids found that DHA levels were significantly lower in patients with dementia compared with healthy elderly controls. Consistent with these findings, a recent unpublished pilot study of lutein/DHA supplementation on cognitive function in older women found an association between serum DHA (but not serum lutein levels) and post-supplementation improvement in cognitive functioning. Large, randomized, controlled interventional studies using DHA will be required to confirm a significant benefit for DHA in prevention and/or reduction of dementia/cognitive impairment in the elderly.