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. Studies have also shown some benefit with cancer patients and in situations of stress. (Dean, Ward, M.D., and John Morgenthaler and Steven Wm. Fowkes. Smart Drugs II, Melatonin Chapter. Smart Publications. 2000. Article.)
Refer to Sleep and the Brain for additional information.