We've all heard that eight hours of sleep a night is optimal, but a new studies suggest that sleeping seven hours could be better.

One study shows brain function peaks after seven hours of sleep before declining. Another study finds that the mortality rate is lower among those who sleep between 6.5 and 7.5 hours a night.

But whatever amont of sleep you get, experts agree skimping on a full night's sleep impairs performance and memory. It can even cause weight gain.