Research has shown that humans really don't need 8hrs sleep to work at their optimal best and 4-5 hrs of sleep should be more than enough. Citation please? It'

Research has shown that humans really don't need 8hrs sleep to work at their optimal best and 4-5 hrs of sleep should be more than enough. Citation please? It's my understanding that losing even 1 hour of sleep a night will add up over time and cause all sorts of cognitive problems.