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Hot topic - Sleep longer, stay slimmer18 January 2005 - written by BUPA's Health information team Reduced amounts of sleep may be linked to being overweight and obese, according to a new US study published in the 10 January 2005 edition of the Archives of Internal Medicine.1 What did the study show?The study showed that men and women who were overweight or obese tended to sleep for a shorter amount of time each night compared with those with a normal body mass index (BMI). People with a normal BMI slept an average of 16 minutes longer each day. However, people who were severely obese did not necessarily sleep less than those with a normal BMI.1 What is a normal body mass index (BMI)?Body mass index (BMI) is the most common benchmark for healthy weight of adults. It is a measurement based on height and weight. It can be calculated using the formula:
People with a BMI of over 18.5 to 25 are considered to be a healthy weight.2 What is an overweight or obese body mass index (BMI)?An overweight BMI ranges from 25 to 30 and an obese BMI ranges from 30 to 40. This table shows the way different BMIs are classified:2
People are defined as being "morbidly obese" if they have a BMI of over 40, or a BMI of 35 to 40 in the presence of other significant co-morbid conditions (such as diabetes or high blood pressure) that could be improved by weight loss. Who took part in the study?The study included 1001 men and women aged between 18 and 91 years.1 How was the study carried out?Patients had their height and weight measured and were grouped according to their BMI. The patients completed questionnaires about personal characteristics (age, sex, etc), medical problems and their sleep patterns, including any sleep disorders. The study looked at the relationship between BMI and the average total number of hours slept over a 24-hour period.1 Why may less sleep be linked to obesity?There is growing evidence to suggest that missing out on sleep can increase appetite. Lack of sleep has been associated with increased levels of a hormone called ghrelin and decreased levels of the hormone leptin.1,3 What do these hormones do?Ghrelin increases appetite, and is released by the stomach to stimulate hunger. Leptin reduces appetite and is released by fat cells in the body. These two hormones are thought to work together. So when leptin levels are lower or ghrelin levels are increased, ghrelin becomes the dominant hormone. It sends a signal to the brain, you then feel hungry, and are prompted to eat. Sleep loss may affect the levels of these hormones that control appetite.3,4 What did the study conclude?The study concluded that reduced amounts of sleep are associated with being overweight and obese. However, reduced amounts of sleep were not necessarily associated with being severely obese. The findings suggest that lots of extra sleep may not be needed. An extra 20 minutes of sleep each night may be linked to a lower BMI.1 How much sleep should I be getting?It depends mainly on your age and how much exercise you get. But there isn't a set number of hours that you should be sleeping every day. Most adults need between seven and eight hours sleep each day, but some people get by on less and others need more.5 Why do I need sleep?The exact benefit of sleep is not certain. Some people think that it simply allows you to rest and refresh yourself. Others believe that sleep is involved in processing memories. It's clear that a lack of sleep is likely to leave you feeling tired, having difficulty concentrating and lacking energy.6,7 Some researchers think that regularly having too little sleep could increase your risk of getting infections and play a part in the development of diabetes, as well as obesity.7 For more information about diabetes, please see our factsheet: What can I do to make sure I get a good night's sleep?
Further informationBUPA resources: External resources:
References
All websites accessed on 13/01/05
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