>>260189genetics. some people sleep more efficiently so they need to sleep less to fully recover
I've looked into this occasionally in the past month and here's what I found (I won't post links or names, this is just from memory but should be easy to google):
-scientists recommend 7 to 9 hours of sleep for adults. kids and teenagers need more
-they studied mortality rates based on how much people sleep, and those who slept 7 hours actually had the lowest mortality. sleeping less or more than than increased your mortality, but interestingly enough it seens sleeping a lot (10+ hours) was worse than sleeping less (6 or less). I had a graph for this but I'll try to find it another day since I'm about to sleep now
-scientists studied modern day hunter gatherers and found that while they stay in bed for 8 hours, they actually sleep for only 5-7 hours of that time