The effects of docosahexaenoic acid supplementation on cognition and well‐being in mild cognitive impairment: A 12‐month randomised controlled trial

Objectives Several recent clinical trials have shown that docosahexaenoic acid (DHA) supplements have a significant effect on cognition in cognitively impaired older adults. This randomised controlled trial aimed to investigate the cognitive effects of a DHA fish oil supplement in older adults with mild cognitive impairment, and to examine the moderating effect of the apolipoprotein E (APOE) ɛ4 allele on cognition and well‐being. Methods/Design Seventy‐two older adults between the ages of 60 and 90 from New Zealand were given a DHA supplement equivalent to 1491 mg DHA + 351 mg eicosapentaenoic acid per day or a placebo for a period of 12 months. Outcome measures included cognition, wellbeing and self‐rated quality of life as well as height, weight, blood pressure and APOE genotyping. Results The final analysis (n = 60) found no evidence of a treatment effect on cognitive measures, although did find a treatment effect on systolic blood pressure (p = 0.03, ƞ2 = 0.08), and a treatment interaction for APOE ɛ4 carriers on depression (p = 0.04, ƞ2 = 0.07) and anxiety (p = 0.02, ƞ2 = 0.09) scores in favour of the DHA supplement. Conclusions Despite no effect on cognition, the positive result in APOE ɛ4 carriers on depression and anxiety scores and on systolic blood pressure justifies further DHA trials. It may be a prudent step going forward for more studies to replicate the design elements (dose, duration and cognitive measures) of previous DHA trials to help understand why not all older adults appear to benefit from taking a fish oil supplement. Key points Diet underlies the main risk factors for dementia including diabetes and hypertension. Docosahexaenoic acid (DHA) has been shown to have a significant effect on cognition in impaired older adults. Older adults who carry the apolipoprotein E (APOE) ɛ4 allele are at higher risk of cognitive decline. DHA and eicosapentaenoic acid can decrease depression and anxiety scores in APOE ɛ4 carriers.