[gwern]

Old people pretty much are sleep deprived, though. Their systems are falling apart (that's aging). I was reading a study once on, I think, melatonin in the elderly, and it showed a graph of the 24-hour melatonin secretion cycle for a young healthy sample and then for like age 60+ people; in the young people, the cycle looks exactly as one would expect, with a fall in mid-day, increase in evening, and high levels while asleep during the night and slowly declining to the day levels - in the elderly, it was a flat line. Horrifying.