From the article, "'The problem with these studies is that they give you good information about association but not causation,' said Timothy Morgenthaler, presi

From the article, "'The problem with these studies is that they give you good information about association but not causation,' said Timothy Morgenthaler, president of the American Academy of Sleep Medicine, which represents sleep doctors and researchers, and a professor of medicine at the Mayo Clinic Center for Sleep Medicine." Yep. It's painfully difficult and expensive to conduct a good randomized treatment-control study of sleep duration with an adequate sample size for figuring out what is optimal as a population central tendency. I think the observation that many people put in a quiet, dark room in daylight hours will fall asleep is one hint that more Americans get too little sleep than too much sleep at night, but there is still more research needed. When I used to live in the subtropical zone of Taiwan (the latitude of Taipei is about like the latitude of Miami, and the climate is not greatly different), there was still a fairly strongly established cultural custom of taking a nap, a siesta, after lunch. It look me a long time to get used to doing that, but it seemed to make sense, especially in the summer. Sleep patterns vary somewhat by culture and by climate, but the big influence on sleep patterns in the twenty-first century appears to be artificial indoor light, which is much brighter and much less expensive compared to average wages all over the world than it used to be. I always encourage people with sleep problems to get outdoors IN THE MORNING DAYLIGHT for moderate exercise to entrain their bodies' biological clocks. Behavior genetic research shows that the biological clock genes are deeply conserved in most animals, so that basically the same set of genes controls the biological clocks of both fruit flies and human beings. Some flies (and some humans) have gene variants that bring about problems like delayed-sleep-cycle sydrome, but essentially everyone can entrain their biological clock by controlling light exposure.