Endogenous melatonin levels and the fate of exogenous melatonin: age effects.

This study examines the range of serum melatonin concentrations that occur among young and older adults, and tests the effects of orally administered melatonin on the serum and saliva concentrations of the hormone. Healthy volunteers (20-36 per study), aged 20-73 years, were divided into two groups on the basis of age (29.2 +/- 6.5 and 60 +/- 8.8 years). For study 1: Serum melatonin levels were measured at 15 to 60 min intervals over a 25 h period using a radioimmunoassay. For study 2: serum and saliva melatonin levels were measured before and at intervals after the administration of a 0.3 mg dose of melatonin at 11.00 h. The younger subjects had significantly higher peak endogenous melatonin concentrations (+/- SD) and greater inter-individual variability (100.9 +/- 48.6 pg/ml) than the older subjects (34.5 +/- 15.4 pg/ml). Mean melatonin levels following treatment with the hormone tended to be higher and were significantly more variable among the group of older volunteers (254.5 +/- 145.7) than among the younger group (170.2 +/- 22.0 pg/ml). We conclude that although the peak endogenous serum melatonin levels are lower in elderly adults, the increment in serum melatonin levels induced by a low oral dose of the hormone is greater and more variable among people over 48 years old.