According to new research by scientists in New Zealand children who do not get enough sleep face an increased risk of obesity and behavioral problems.
The scientists from the University of Auckland say they have found that seven-year-olds who had less than nine hours per night were more than three times more likely to be overweight or obese than those who slept for longer.
The researchers led by Professor Ed Mitchell, suggest that when sleeping time is restricted it leads to hormonal changes in the stomach and in fat cells that trigger increased appetite.
Professor Mitchell says sleep is important for health and well-being throughout life and paying attention to sleep in childhood may be an important strategy to reduce the obesity epidemic.
Professor Mitchell says their study results show a strong effect of short sleep duration on the risk of obesity which is independent of physical activity or television watching and remained even when levels of daytime activity were adjusted for.
Professor Mitchell and his colleagues studied the sleep patterns of a group of 519 children from Auckland using an electronic device called an actigraph (a non-invasive method used to study sleep-wake patterns and circadian rhythms by assessing movement).
This was done at four different stages of their lives: at birth, at one year, at three-and-a-half years and at seven years.
These were then used along with measurements of height, weight, body mass index (BMI) and body fat levels taken for each participant.
BMI is calculated by multiplying weight in kilograms by height in metres squared. A BMI of 20 to 25 is considered normal, 25 to 30 overweight, and over 30 obese.
The average length of sleep was 10 hours and six minutes but sleep duration was found to be shorter on weekends than on weekdays, in the summer, in those with no younger siblings and when bedtime was after 9:00 p.m.
It was also found that children who slept for on average nine hours per night or less were 3.3 times more likely to be overweight or obese than those who slept for more than nine hours.
These children also had an average of 3.3 per cent more body fat and were more likely to have frequent mood swings.
The researchers believe lack of sleep leads to increased production of ghrelin, a hormone produced in the stomach, and reduced release of the hormone leptin in fat cells; both of these changes have been shown in previous studies to stimulate appetite.
Other research also published this week by researchers from the University of Chicago Medical Centre has found that a lack of sleep, especially deep or slow-wave sleep, reduces the body's ability to regulate blood sugar levels, increasing the risk of Type 2 diabetes, which is linked to obesity.