Lack of enough sleep can lead to some serious health risks. The chart below shows the effects of sleep deprivation. Effects on the brain include irritability, severe yawning, memory lapses or loss, impaired moral judgement, symptoms similar to Attention Deficit Disorder (ADHD) and increased risk of cognitive impairment and hallucinations. Effects on the heart include risk of heart disease and increased heart rate variability. Other effects of sleep deprivation are impaired immune system, increased reaction time, decreased accuracy, tremors, aches, risk of type 2 diabetes, growth suppression, risk of obesity, and disruption of thermoregulation. These symptoms may sound extreme but many teenagers suffer from them. Only eight percent of American teenagers get nine hours of sleep (which is what they need) and are at no risk of experiencing these symptoms (National Sleep Foundation). All of these symptoms could be avoided if teenagers were allowed to get more sleep by having schools start later.