Effects of Omega-3 Fatty Acids on Cognitive Function with Aging, Dementia, and Neurological Diseases
Published in: Evidence report/technology assessment no. 114 (Prepared by Southern California/RAND Evidence-based Practice Center, under Contract No. 290-02- 0003). AHRQ Publication No. 05-E011-2. (Rockville, MD: Agency for Healthcare Research and Quality, Feb. 2005), 144 p
Posted on RAND.org on December 31, 2004
CONTEXT: It has been suggested that omega 3-fatty acids have beneficial effects in several conditions and disorders affecting the central nervous system, including providing a protective effect on cognitive function with aging; dementia, particularly senile dementia of the Alzheimer's type; multiple sclerosis and some of the peroxisomal biogenesis disorders. OBJECTIVES: To assess the effect of omega-3 fatty acids on 1) cognitive function in normal aging 2) the incidence of dementia, 3) treatment of dementia, 4) the incidence of several neurological diseases, and 5) clinical outcomes related to the progression of multiple sclerosis. DATA SOURCES: The authors searched computerized databases to identify potentially relevant studies and contacted industry experts for unpublished data. STUDY SELECTION: The authors screened 5,865 titles, reviewed 497 studies - of which 62 underwent a detailed review, and found 12 studies that pertained to our objectives. The authors included controlled clinical trials and observational studies, including prospective cohort, case-control, and case series designs; they excluded case reports. The authors had no language restrictions. DATA EXTRACTION: The authors abstracted data on the effects of omega-3 fatty acids and on study design; relevant outcomes; study population; source, type, amount, and duration of omega-3 fatty acid consumption; and parameters of methodologic quality. DATA SYNTHESIS: 1) A single cohort study has assessed the effects of omega-3 fatty acids on cognitive function with normal aging and found no association for fish or total omega-3 consumption. 2 and 3) In four studies (3 prospective cohort studies and one RCT) that assessed the effects of omega-3 fatty acids on incidence and treatment of dementia, a trend in favor of omega-3 fatty acids (fish and total omega-3 consumption) toward reducing risk of dementia and improving cognitive function was reported. 4) Two studies, one cohort and one case-control, that assessed the effects of omega-3 fatty acids on incidence of MS were inconclusive. A single cohort study evaluating the effects of omega-3 fatty acids on incidence of Parkinson₂s disease found no significant association between dietary intake of omega 3 fatty acids (fish, ALA, EPA, or DHA) and Parkinson's. Another single case-control study found a significant association between maternal fish consumption at least once a week throughout pregnancy and a lower risk of cerebral palsy in offspring. 5) In one RCT, omega-3 fatty acids (fish, ALA, EPA, DHA) had no effect on the progression of multiple sclerosis; two single-arm open-label trials showed improvement in disability with omega-3 supplementation. CONCLUSIONS: The quantity and strength of evidence for effects of omega-3 fatty acids on the neurological conditions assessed vary greatly. Due to the small number of studies that met our inclusion criteria, further research is necessary before substantive conclusions can be drawn. The paucity of evidence in this area suggests that a great deal of epidemiological and clinical research remains to be done before any conclusions can be drawn or policy recommendations can be made regarding the health effects of omega-3 fatty acids on normal cognitive function with aging, dementia, and neurological diseases.