What does sleep do for us? Get enough (as few Americans do) and your odds of living a longer and more healthy life go up. Poor sleep is a risk factor for depression and substance abuse. The lack of sleep has been linked with weight gain and elevated risks of cancer and heart disease. In children, the need for sleep is even more profound. More and better sleep is associated with higher test scores and happiness, while the lack of it can lead to everything from a mistaken diagnosis of attention deficit hyperactivity disorder to hormonal disruptions.