When you were young, your mother may have told you that you need to get enough sleep to grow strong and tall. She may have been right! Deep sleep triggers more release of growth hormone, which fuels growth in children and boosts muscle mass and the repair of cells and tissues in children and adults. Sleep’s effect on the release of sex hormones also encourages puberty and fertility.
Consequently, women who work at night and tend to lack sleep are, therefore, more likely to have trouble conceiving or to miscarry. Your mother also probably was right if she told you that getting a good night’s sleep on a regular basis would help keep you from getting sick and help you get better if you do get sick. During sleep, your body creates more cytokines—cellular hormones that help the immune system fight various infections. Lack of sleep can reduce the ability to fight off common infections. Research also reveals that a lack of sleep can reduce the body’s response to the flu vaccine.
For example, sleep-deprived volunteers given the flu vaccine produced less than half as many flu antibodies as those who were well rested and given the same vaccine. Although lack of exercise and other factors are important contributors, the current epidemic of diabetes and obesity appears to be related, at least in part, to chronically getting inadequate sleep.
Evidence is growing that sleep is a powerful regulator of appetite, energy use, and weight control. During sleep, the body’s production of the appetite suppressor leptin increases, and the appetite stimulant grehlin decreases. Studies find that the less people sleep, the more likely they are to be overweight or obese and prefer eating foods that are higher in calories and carbohydrates. People who report an average total sleep time of 5 hours a night, for example, are much more likely to become obese compared to people who sleep 7–8 hours a night.
A number of hormones released during sleep also control the body’s use of energy. A distinct rise and fall of blood sugar levels during sleep appears to be linked to sleep stage. Not getting enough sleep overall or enough of each stage of sleep disrupts this pattern. One study found that, when healthy young men slept only 4 hours a night for 6 nights in a row, their insulin and blood sugar levels mimicked those seen in people who were developing diabetes. Another study found that women who slept less than 7 hours a night were more likely to develop diabetes over time than those who slept between 7 and 8 hours a night.