APOE and major depressive disorder: The potential mechanisms underlying the interaction between handgrip strength, vitamin D, and APOE genotype remains unclear, and the explain may be that both optimal handgrip strength and vitamin D were associated with lower risk of dementia-related risk factors, such as stroke, diabetes, and depression [39, 41], while studies have confirmed significantly interaction between the aforementioned risk factors and APOE genotype in relation to dementia or cognitive function [42, 43].