No effect of n-3 long-chain polyunsaturated fatty acid (EPA and DHA) supplementation on depressed mood and cognitive function: a randomised controlled trial

Randomized placebo-controlled trial in adults aged 18 to 70 years with mild to moderate depressive symptoms, recruited mainly from general practice surgeries and community settings in Bristol, United Kingdom. Participants were not pregnant or breast feeding, were not severely ill, were not taking antidepressant medication, and were fluent English speakers.

Participants took three capsules daily by mouth for 12 weeks. The active regimen provided 630 mg EPA and 850 mg DHA per day, with olive oil, mixed tocopherols, and orange oil as capsule constituents; the comparator was matching placebo capsules containing olive oil and the same minor ingredients.

EPA and DHA supplementation did not improve depressed mood or cognitive function over 12 weeks. For the primary DASS depression outcome, the week-12 adjusted difference was -1.0 (95% CI -2.83, 0.81; P = 0.27), indicating no statistically significant benefit versus placebo. Other mood-related measures were also null, including Beck Depression Inventory at week 12 (P = 0.44), General Health Questionnaire (P = 0.88), and STAXI state anger (P = 0.46). The overall conclusion was that n-3 long-chain polyunsaturated fatty acid supplementation produced no meaningful benefit, and meta-analysis including this trial suggested a negligible effect on depressed mood.

The intervention lasted only 12 weeks, so longer-term effects were not assessed. The population had mild to moderate depressive symptoms rather than major depression, limiting applicability to more clinically severe depression. Recruitment was from a single geographic area, and the available excerpt provides limited detail on cognitive outcomes and on whether the study was powered to detect small effects.