I suppose that it is well-known that different people need different amounts of sleep. I read somewhere that most people need something between 7 and 8 hours each day, though some people need only 6 hours, and (for instance) I have two friends who only need 5 hours. Q: Besides genetic factors, what determines a healthy individual's required amount of sleep?For example: Is there a correlation between an individual's g factor and their required amount of sleep? Is there a correlation between an individual's weight and their required amount of sleep?Note: I am not interested in findings related to infants or teenagers. 
What factors determine a healthy individual's required amount of sleep?
sleep