This paper confirms in some detail the old clinical pearl that sensory loss is associated with dementia, and shows a dose response as well. In addition to the potential mechanisms thoughtfully discussed here, it's also possible that sensory loss could simply contribute to the functional decline necessary to cross the threshold for dementia. It's that much harder to manage a wide variety of life tasks when a critical information source is lost, so people with hearing loss would be expected to have more functional impairment for a given level of cognitive loss or underlying brain pathology.
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.
PubMed.
Comments
This paper confirms in some detail the old clinical pearl that sensory loss is associated with dementia, and shows a dose response as well. In addition to the potential mechanisms thoughtfully discussed here, it's also possible that sensory loss could simply contribute to the functional decline necessary to cross the threshold for dementia. It's that much harder to manage a wide variety of life tasks when a critical information source is lost, so people with hearing loss would be expected to have more functional impairment for a given level of cognitive loss or underlying brain pathology.
Weill Cornell Medical College
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. PubMed.
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