Every two years for 16 years, the Nurses Health Study collected data from more than 68,000 women ages 40 to 65, which included information on sleep habits and body weight. The study found that participants who slept five hours a night were 32 percent more likely to experience a weight gain of 33 pounds or greater, and 15 percent more likely to become obese, compared with participants who slept seven hours a night.
The group who slept for six hours were 12 percent more likely to experience major weight gain and six percent more likely to become obese when compared with those who slept seven hours a night. One possible explanation for these differences is that lack of sleep causes the body to burn calories less efficiently. Variations in eating habits and exercise among the groups also explained some of the weight gain, although no single factor can be pinpointed.
The amount and quality of sleep affects hormones that regulate appetite and metabolism. A study at the University of Chicago found that participants who slept only four hours a night for two nights had an 18 percent decrease in leptin and a 28 percent increase in ghrelin. Leptin is a hormone that suppresses appetite by affecting how full and satisfied we feel after eating. Ghrelin is a hormone that stimulates appetite.
With sleep deprivation, levels of leptin fall, while ghrelin levels increase. Participants in the study, all healthy young men, showed a 24 percent increase in appetite along with elevated cravings for sweets, salty foods and starchy foods like bread and pasta. Leptin is only one of a large number of genes that can influence body weight, while environment and lifestyle behaviors remain the primary causes of weight gain.
When a person is fatigued from too little sleep, they are also less likely to exercise, making it easier to put on extra pounds.
Lack of sleep affects other hormones such as cortisol, insulin and growth hormone, potentially causing a desire for high-calorie foods.
It is believed that decreased amounts of REM sleep can lead to increased food intake. REM stands for "Rapid Eye Movement" and is the "dream" phase of the sleep cycle. During REM sleep brain activity increases with less muscle activity.
Aside from the potential increase in body weight, sleep deprivation can have serious effects on physical and mental health.
When the brain has to work harder in an effort to counteract sleep deficit, its ability to function deteriorates quickly. Memory, concentration and problem-solving capabilities decrease. The ability to handle everyday stress, maintain a healthy immune system and control emotions is also compromised.
It is recommended that children ages 3 to 5 years get 11 to 13 hours of sleep per night; ages 5 to 12, 9 to 11 hours; and adolescents, 8.5 to 9.5 hours. Although most experts recommend seven to nine hours of sleep a night for adults, the exact amount needed to function at our best varies from person to person.
What about napping? A study at NASA on sleep-deprived military pilots and astronauts showed that taking a 40-minute nap improved performance by 34 percent and alertness 100 percent. Naps that are too long or taken too late in the day, however, affect the quality of nighttime sleep, so proper planning is important. Generally, a 20- to 30-minute nap is enough time to reap the benefits of increased alertness and performance and improved mood.