Changes in tension (p = 0.014, Hedge’s g = 0.74), depression (p = 0.003, Hedge’s g = 0.90), anger (p = 0.043, Hedge’s g = 0.60), confusion (p = 0.028, Hedge’s g = 0.66), total mood disturbance (TMD) (p = 0.016, Hedge’s g = 0.72) and SMCs (p = 0.015, Hedge’s g = 0.75) following fish oil supplementation were significantly different between APOE4 carriers and non-carriers. Here, APOE is linked to major depressive disorder.