Dietary caloric restriction prevents the age-related decline in plasma melatonin levels of rhesus monkeys

Rhesus monkeys exhibit an age-associated decrease in peak. plasma melatonin levels analogous to that reported for humans. This decrease is essentially abolished in monkeys subjected to a 30% reduction in caloric intake over a 12-yr period. The caloric restriction (CR) effect does not seem to be a re versal, but rather a long-term prevention, of the age-related decline in ho rmone concentrations. The age effect does not seem to be due to a phase shi ft in the peak of melatonin secretions, as has been observed in some popula tions of aged humans. It is also extremely unlikely that; the CR effect sim ply reflects a phase shift, since old monkeys on the diet have nocturnal me latonin levels equal to or greater than adult fully fed controls Thus, if p eak times (approximately 0200 h) were actually shifted, maximal levels in o ld CR monkeys would be even higher. These findings, coupled with previous o bservations in humans, suggest that peak plasma melatonin levels may repres ent a possible candidate "biomarker of aging" in primates. Moreover, this i ndex of age-associated physiological decrement seems to be inhibited by die tary CR.