Melatonin and aging

Abstract

Both normal aging and dementia are associated with disturbances in the biological clock that contribute to significant circadian disorganization, including impaired sleepwake cycles, deranged daily body temperature rhythm, and disrupted daily patterns of hormone release (Wu and Swaab, 2007), including nightly melatonin secretion. Generally, aging is associated with reduced amplitudes among daily rhythms; the most severe changes are associated with patients with Alzheimer's disease (AD) (Van Someren, 2000). Circadian disorders affect > 80% of individuals over age 65 because of several converging factors; loss of neurons in the suprachiasmatic nucleus, decreased melatonin and melatonin receptor sensitivity, and minimal zeitgebers because of lifestyle all contribute to circadian dysfunction (Foley et al., 1995; Duncan, 2007; Wu and Schwab, 2007). Reduced melatonin and melatonin receptor sensitivity have been reported among aged individuals (Skene and Swaab, 2003; Wu and Swaab, 2005). However, because melatonin receptors are substantially reduced in the suprachiasmatic nucleus of elderly and AD individuals, there may be too little substrate for melatonin supplementation to have an effect (Wu et al., 2007). The goal of this article is to review the known effects of melatonin on aging and the extent to which diminished endogenous melatonin can be supplemented to ameliorate the effects of aging in several physiological or behavioral systems. Below, we briefly review the production of melatonin, its mechanisms of actions, distribution of melatonin receptors, effects of aging, as well as how melatonin can affect aging processes.