We added a study to the depression section of the omega 3s research page:
A 2019 meta-analysis and systematic review of 32 randomized controlled trials found little to no effect of increasing EPA and DHA on risk of depression symptoms (RR 1.01, CI 0.92-1.10). Studies had a median duration of 12 months with a median dose of 0.95 grams per day (ranging from 0.4 to 3.4 grams per day). One study addressed omega-3s and anxiety and found little to no effect. The researchers recommend against taking omega-3 supplements for reducing depression and anxiety risk.
Deane KHO, Jimoh OF, Biswas P, et al. Omega-3 and polyunsaturated fat for prevention of depression and anxiety symptoms: systematic review and meta-analysis of randomised trials [published online ahead of print, 2019 Oct 24]. Br J Psychiatry. 2019;1‐8.