Dehydration, formaldehyde, and age-related cognitive impairment

Abstract

Chronic dehydration is regarded as a common symptom of patients with age-related cognitive impairment, particularly those with Alzheimer's disease. It has been known that chronic dehydration causes not only serum hyperosmotic pressure increase but also metabolic dysfunction of the central nervous system and cognitive impairment. Recently, imbalance of anabolism and catabolism of endogenous formaldehyde has been considered as one of the risk factors involving age-related cognitive impairment. Formaldehyde at low concentration induces the senile plaques (amyloid ß deposition), neurofibrillary-like tangles (containing tau hyperphosphorylation), and cognitive impairment in the brain of monkeys. The levels of endogenous formaldehyde of inpatients were markedly higher than those of the age-matched participants. Thus, we are concerned about the relationship between cognitive impairment and water intake behavior as well as that between dehydration and dysmetabolism of endogenous formaldehyde with aging. As a result of aging, serum AVP concentration and brain endogenous formaldehyde levels increase. Excess formaldehyde could activate ANG II to promote AVP expression. Meanwhile, elevation of AVP activates semicarbazide-sensitive amine oxidase (SSAO) to produce more endogenous formaldehyde. These pathways could create a "vicious cycle" worsening water intake behavior that both drinking frequency and quantity decrease. That is, at least, dysmetabolism of endogenous formaldehyde can affect water intake behaviors. The highest concentration of endogenous formaldehyde is found in the morning, followed by a decrease around noon and an increase in the evening. Therefore, regular water intake including tea or other beverages containing resveratrol is recommended to intervene and reduce the accumulation of formaldehyde in the human body, especially when it is taken in the morning.