MTHFR and hearing loss disorder: We investigated the effects of the methionine synthase (MTR) A2756G and MTHFR C677T gene polymorphisms on the risk for hearing impairment in community-dwelling Japanese adults aged 40–84 years who participated in the National Institute for Longevity Sciences, Longitudinal Study of Aging (NILS-LSA), an ongoing population-based biennial study.