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I'm always amazed at the ingenuity of researchers when I read about the avenues they explore to find out more about the problems that beset humanity.
When I came across a review article summarising the latest research that's being done to determine if adequate sleep can help us to lose weight, I was fascinated. It had never crossed my mind that the hours of sleep adults and children get at night can influence their body weight and insulin metabolism.
But as Drs Eve Van Cauter and Kirsten Knutson explain in their article on “Sleep and the epidemic of obesity in children and adults", published in December 2008, sleep can play a vital role in helping people to stay slim.
Van Cauter and Knutson (2008) point out that the obesity pandemic that's sweeping through the world has been accompanied not only by increasing food intake and lack of physical exercise, but also by shorter habitual sleep times.
They emphasise that a condition called "sleep curtailment" is becoming more and more prevalent in countries like America. Statistics from 1960 found that adults slept between 8 and 8.9 hours per night, but by 1995 this figure had dropped to 7 hours per night. Nowadays, up to 30% of adult men and women sleep less than 6 hours per night, and more than 30% of the population are overweight or obese.
Studies with teenagers reported that instead of sleeping 9 hours a night as is recommended, adolescents tend to sleep less and less as they get older, until by the age of 18-19 years they're only sleeping 6.9 hours a night.
Effects of sleep curtailment
According to the researchers, not sleeping long enough at night may affect body weight in three ways:
- Increased appetite
- Provide individuals with more time to eat when they're awake for longer
- Decreased energy output
Research studies
a) The ‘Sleep Debt Study’
This study was conducted with healthy young men who were exposed to "sleep debt" (only being allowed to sleep for 4 hours per night, for a period of 6 days. The test period was followed by 7 nights during which the subjects had 12 hours of sleep.
All the men followed the same diet and were tested for glucose tolerance. Blood samples were drawn for 24 hours to determine if the sleep debt had an influence on certain factors that affect weight gain.
The following results show that it did indeed have a marked effect on weight-control factors in the experimental subjects:
- Their leptin levels were 19% lower when they had a sleep dept. Leptin is a compound that signals satiety and stops food consumption in the body. The lower the leptin levels, the hungrier the person will feel and the greater the food intake.
- Their cortisol levels increased in the late afternoon and evening , which would also stimulate increased food intake.
- Their glucose tolerance results decreased by 40%, so that the subjects appeared to suffer from impaired glucose tolerance and reduced insulin sensitivity (both are characteristic of insulin resistance, which is strongly linked to weight gain).
b) Recurrent sleep restriction trial
Researchers at the University of Chicago (Nedeltcheva et al, 2009) studied 11 healthy volunteers in a laboratory setting. The subjects were allowed to eat as much food as they liked, but were not allowed to exercise.
During two 14-day periods, the subjects were either allowed to have 5.5 or 8.5 hours of sleep during the night. Blood samples were analysed for a variety of factors that influence weight gain and type 2 diabetes.
The Chicago team also found that during the sleep deprivation periods, the subjects had reduced glucose tolerance and reduced insulin sensitivity, which can contribute to the development of obesity and type 2 diabetes.
Children and teenagers at risk
Some scientists warn that lack of sufficient sleep may have a greater impact on the risk of obesity in children and adolescents than in adults.
The root of the problem?
Van Cauter and Knutson suggest that the decrease in leptin, the increase in grehlin and the reduction in insulin sensitivity may be responsible for the link between lack of sleep and obesity.
According to these researchers, there are two chemicals in the human body called orexins (orexin A and orexin B), which are produced in the lateral hypothalamus in the brain. Orexins help to keep the body awake and stimulate processes such as eating. They suggest that orexins may be responsible for the changes in leptin and insulin sensitivity observed in sleep-deprived experimental subjects.
Go get some shut-eye
So, although there are many things we don’t yet know about how sleep influences weight gain, obesity and the development of insulin resistance and type 2 diabetes, it seems that getting enough sleep can affect your weight and health.
If you're one of those people who doesn't manage to get to bed before midnight and then gets up at 5am, you may just be fuelling your overweight and putting yourself at risk of diabetes.
Adults should all make it a goal to have at least 7 hours of proper sleep at night. For children, sleep is even more important, so try to persuade those young night owls in your family to get at least 9 hours of sleep.
(Dr I.V. van Heerden, DietDoc, July 2009)
References:
(Nedeltcheva et al (2009). Exposure to recurrent sleep restriction in the setting of high caloric intake and physical inactivity results in increased insulin resistance and reduced glucose tolerance. J Clin Endocrinol Metab, June 30 2009; Epub ahead of print]; Van Cauter E & Knutson KL (2008). Sleep and the epidemic of obesity in children and adults. Euro J Endocrinol, 159:S59-S66.)
