Proper Sleep
Sleep Timing and Regularity
"Timing your sleep is like timing an investment in the stock market – it doesn’t matter how much you invest, it matters when you invest."
http://www.doctoroz.com/blog/kulreet-chaudhary-md/sleep-and-longevity
"Shift workers who regularly work different hours, those who work at night, and people frequently flying long-distance routes across time zones have a substantially increased risk of breast and prostate cancer, and suffer higher rates of stroke, heart attack, diabetes, weight gain, mood and other psychological factors."
References at http://www.growyouthful.com/remedy/regular-daily-habits-schedule.php
Sleep Duration
of 21,000 case studies with twins - "if people slept less than 7 hours a night or more than 8 hours a night, they had an increased risk of death. For short sleep women, that increase was 21% (men: 26%) and for long sleeping women, the increase was 17% (men: 24%)."
http://longevity.about.com/od/sleephealthandaging/a/sleep_duration.htm
But also, there are some high energy people for whom 4 hours of sleep is fine.