Nothing Fishy about Preventing Cognitive Decline

The prevalence of dementia and age-related cognitive decline is increasing around the world as the population ages and life-expectancy increases. Many interventions have been examined that may slow or prevent the onset of cognitive impairment; one of the simplest and most cost-effective interventions studied is the dietary intake of omega-3 fatty acids. Unfortunately, a new study, published in the American Journal of Clinical Nutrition, reports that the use of fish-oil supplements has no effect on cognitive function.

Omega-3 long-chain polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are critical in human brain development and function. These fatty acids regulate neuronal function and regulate oxidative stress to maintain brain health and prevent disease. These fatty acids are found in breast milk and infant formula to promote brain and eye growth and development. As humans age, most consumption of omega-3 fatty acids comes from consuming oily, cold water fish such as salmon, tuna, herring, and mackerel. Dietary intake is essential, as the body cannot synthesize these fatty acids on its own.

Many epidemiological studies have touted the benefits of a diet rich in fish, and have associated omega-3 fatty acid intake with a reduced risk of age-related cognitive decline and dementia. Omega-3 fatty acids are also believed to be protective against risk factors for dementia, including diabetes, head trauma, and cardiovascular disease. To test this hypothesis, researchers in the United Kingdom conducted a randomized, double-blind, controlled study of 867 adults aged 70 to 79. The participants were in good physical and cognitive health at the beginning of the study, but did not take fish-oil supplements. The mean age of study participants was 75 years and 55% of them were men.

Participants were assigned to receive a daily supplement containing 200 mg of EPA and 500 mg DHA or an olive oil placebo. (The doses of omega-3 fatty acids are equivalent to consuming 1 to 2 portions of oily fish every week.) Baseline blood levels of EPA and DHA were obtained and standardized memory and cognitive function tests were conducted at the beginning of the study. Follow-up measurements were obtained 24 months later at the end of the study.  After 2 years, the participants in the fish-oil group had higher blood levels of DHA and EPA than the control group. There was no cognitive decline observed in either group and no other differences in cognitive function were detected.

Researchers hoped to use this study to identify simple, cost-effective behaviors that could reduce the risk of cognitive decline in older adults. Fish oil supplementation does not appear to be such a behavior. This may be due, in part, to the relative good health of the subjects to begin with. Many were already consuming adequate amounts of oily fish in their diet before the study began. However, the results of the study may indicate that increasing late-life dietary intake of omega-3 fatty acids may not be as beneficial as lifelong healthy eating habits that include regular consumption of oily fish. Additionally, the benefits of omega-3 fatty acids may be moderated by other dietary or lifestyle factors or may be related to the stage of cognitive decline.

Consuming fish or the omega-3 fatty acids found in fish are reported to improve cardiovascular health, prevent cancer, promote eye health, and treat inflammatory conditions such as rheumatoid arthritis, bowel disease, and systemic lupus; randomized, controlled trials are still needed to define the actual benefits of fish oil. The disappointing results of the current study should not discourage people from eating fish, or even taking fish oil supplements, as part of a healthy diet, but fish oil may not be the panacea it is believed to be.

References

Cole GM, Ma QL, & Frautschy SA (2009). Omega-3 fatty acids and dementia. Prostaglandins, leukotrienes, and essential fatty acids, 81 (2-3), 213-21 PMID: 19523795

Dangour, A., Allen, E., Elbourne, D., Fasey, N., Fletcher, A., Hardy, P., Holder, G., Knight, R., Letley, L., Richards, M., & Uauy, R. (2010). Effect of 2-y n-3 long-chain polyunsaturated fatty acid supplementation on cognitive function in older people: a randomized, double-blind, controlled trial American Journal of Clinical Nutrition DOI: 10.3945/ajcn.2009.29121

Alan, D., Clemens, F., Elbourne, D., Fasey, N., Fletcher, A., Hardy, P., Holder, G., Huppert, F., Knight, R., Letley, L., Richards, M., Truesdale, A., Vickers, M., & Uauy, R. (2006). A randomised controlled trial investigating the effect of n-3 long-chain polyunsaturated fatty acid supplementation on cognitive and retinal function in cognitively healthy older people: the Older People And n-3 Long-chain polyunsaturated fatty acids (OPA Nutrition Journal, 5 (1) DOI: 10.1186/1475-2891-5-20

Jicha GA, & Markesbery WR (2010). Omega-3 fatty acids: potential role in the management of early Alzheimer’s disease. Clinical interventions in aging, 5, 45-61 PMID: 20396634