Effects of n-3 fatty acids, EPA v. DHA, on depressive symptoms, quality of life, memory and executive function in older adults with mild cognitive impairment: a 6-month randomised controlled trial

Randomized controlled trial with treatment allocation by minimisation based on age, sex, and depressive symptoms. The study enrolled adults over 65 years with mild cognitive impairment, not dementia, in Australia, with limited fish intake and no fish oil use in the prior 3 months.

Participants were randomized to four capsules daily for 6 months of either DHA-rich fish oil providing 1.55 g DHA plus 0.40 g EPA per day or EPA-rich fish oil providing 1.67 g EPA plus 0.16 g DHA per day, compared with a linoleic acid control. The active regimens were taken orally in capsule form.

The omega-3 interventions improved depressive symptoms, with both EPA-rich and DHA-rich fish oils reducing GDS scores versus linoleic acid control; the DHA group showed a significant time-by-treatment effect (Estimate 2 1.40, SE 0.53, t 2 2.62, P 0.01, 95% CI 2 2.47, 2 0.32), and improved GDS scores were correlated with increased DHA plus EPA (r 0.39, P 0.02). DHA also improved Initial Letter Fluency versus control (Estimate 4.16, SE 1.99, t 2.09, P 0.04, 95% CI 0.12, 8.21). There were no consistent treatment effects on other cognitive measures or overall quality of life, although Digits Backward improved in the DHA group without reaching significance (P 0.10).

The trial was small, with only 6 months of follow-up and relatively few completers in each active arm. Most cognitive and quality-of-life outcomes were null, so the benefits appear limited mainly to mood and one fluency measure. Generalizability is restricted to older adults with mild cognitive impairment, limited fish intake, and no recent fish oil use.