Melatonin secretion naturally drops off with age causing an age-related “jet-lag,” if you will. Taking melatonin about an hour before bedtime has been shown to improve quality of life in some elderly individuals. Positive correlations with cancer and stress have also be identified. (Dean, Ward, M.D., and John Morgenthaler and Steven Wm. Fowkes. Smart Drugs II, Melatonin Chapter. Smart Publications. 2000. Article)
See Sleep and the Brain for additional information.