A number of studies indicate that reduced hours of deep sleep may result in poorer health, including weight gain and diabetes. A study published in December, 2007, concluded that people who sleep less than 7 hours each night have significantly greater risk of obesity compared to people who sleep 8 to 9 hours. Interestingly, women appear to have increased risk of obesity at both short (less than 7 hours) and long (greater than 9 hours) sleep times. Men only appear to be at risk at short sleep times. Additionally, women are at much more risk from sleep deprivation than men. These risks include increased blood pressure and other heart disease. Over the past 40 years, American adults have cut their sleep time by nearly 2 hours. In 1960 adults averaged 8-1/2 hours of sleep per night; by 2002 that was reduced to less than 7 hours each night. It is thought that weight gain is due to changes in levels of the hormones ghrelin that causes hunger and leptin that causes the feeling of fullness. An older study published in 1999 showed that reduced sleep in young adults caused metabolic changes that mimic the aging process. These changes included alterations in blood glucose control resembling those that occur in diabetes. Reduced sleep also resulted in reduced secretion of thyroid hormone and elevated levels of cortisol. Thyroid hormone helps regulate metabolism, decreased levels of thyroid hormone can result in weight gain and lack of energy. Increased levels of cortisol contribute to health problems such as increased insulin resistance and memory impairment. Other studies link less sleep with the tremendous increase in obesity in children, affecting weight gain in children as young as 5 years old. Adding to the problem is the fact that people get less sleep than they think they do. Participants in a sleep study spent 7-1/2 hours in bed but got less than 7 hours of sleep.

Lack of sleep has long been associated with cognitive changes such as decreased ability to concentrate, trouble learning, decreased attention to detail, and increased risk of traffic accidents. More recent studies indicate that lack of sleep is also associated with medical problems such as obesity, diabetes and high blood pressure.

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