A new forecast estimates climate change could cause people to lose up to two weeks of sleep a year, on average, by the end of the century. The research finds if the low temperature is 77 degrees or warmer, the probability of getting fewer than seven hours of sleep a night increases. "Sleep is important for a lot of functions in the body, everything from our immune system to our heart health, the metabolism, brain health and mental health," said Michael Grander, director of the Sleep and Health Research Program at the University of Arizona.