Staying awake longer than normal may be at the cost of stress-related memory impairment, increased risk of infection and more flab. Cortisol poses the biggest danger. Normally the hormone declines at night to prepare the body for sleep. It increases in the morning to make a person more alert for the coming day's activities. Limiting volunteers to four hours of sleep for just one night caused their cortisol levels to remain high.
People think they can lose sleep.
This is the first study to show that isn't true since the stress hormone level is too high the next night. Cortisol, released by the adrenal gland in response to stress, prepares the body to take action. Production of the hormone subsides once the stressful event is over. The hormone is so powerful the body normally turns it off when it is not needed. Studies in animals and older people show long-term exposure to abnormally high levels of cortisol can damage brain cells, causing shrinkage in the hippocampus, a critical region of the brain that regulates learning and memory.