One other possibility for linking hearing loss to dementia is that both may reflect mitochondrial impairment. Hearing loss occurs with mitochondrial disorders such as MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes). Age-related hearing loss is prevented by caloric restriction, and this is mediated by Sirt3 which regulates isocitrate dehydrogenase, leading to increased NADPH and reduced glutathione in mitochondria (Someya et al., 2010). Sirt3 also plays a role in activation of MnSOD in response to caloric restriction.

References:
Someya S, Yu W, Hallows WC, Xu J, Vann JM, Leeuwenburgh C, Tanokura M, Denu JM, Prolla TA. Sirt3 mediates reduction of oxidative damage and prevention of age-related hearing loss under caloric restriction. Cell. 2010 Nov 24;143(5):802-12. Abstract

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