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Is sleep really the key to fighting obesity?

Health Advisor is a regular column where contributors share their knowledge in fields ranging from fitness to psychology, pediatrics to aging. Follow us @Globe_Health.

More exercise and less food equals weight loss. Now, some experts are ready to recommend improved sleep as another key obesity intervention.

Studies of sleep and obesity have proliferated: A search for medical articles with titles containing both "sleep" and "obesity" revealed 385 publications in the past decade, whereas the previous decade had 63. Examining sleep and obesity is big right now.

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Most researchers who have looked closely at the relationship find an elevated likelihood of obesity in adults who sleep five hours or less, and in children who sleep 10 hours or less. (The data for adolescents are less clear.) These relationships have been observed even in longitudinal, prospective studies that have controlled for various factors like age, sex and physical activity.

A research article released last week in the journal Pediatrics adds to the mounting evidence for a relationship between short sleep and obesity, especially in children. Elsie Taveras from Harvard University and colleagues studied 1,046 children, at age six months and yearly until age 7. At each time point, they asked the mothers to estimate the usual sleep duration of their child. When the child was 7, they took various measurements of "adiposity" (fatness). They found that those children who, over the years, consistently slept less than the age-specific recommended amounts, were the most likely to be obese.

How could it be that our sleep duration may affect our weight? By restricting sleep in adult volunteers over several nights in the lab, some potential mechanisms have emerged. Shortened sleep (e.g., four hours per night) is accompanied by a set of hormonal changes (cortisol, epinephrine, ghrelin, leptin) that promote appetite and weight gain, and that impair the body's ability to balance blood-glucose levels.

A relationship between curtailed sleep and obesity exists and we have possible mechanisms to explain it. However, does it necessarily mean that we can reduce obesity by lengthening our sleep? I saw a headline a few years ago that read: "You snooze, you lose," implying that sleeping is a way to weight management. To know if this is true, we need to determine whether the relationship is causal. It is possible that short sleep causes obesity, but it is also possible that other factors are responsible (so-called upstream factors) such as genetic pathways that link sleep and obesity. I'll use an analogy here: Each evening at dusk, we watch gulls flying over our house, south to the lake. At about that time, we see the shadows in the back yard quickly lengthening. It wouldn't make sense to say that the flying of gulls causes the lengthening of the shadows. Both phenomena are associated with the setting sun. But one way to test that relationship would be to arrange for gulls to fly over at different times of day and to see if the shadows similarly lengthened with each overflight.

So, we can't automatically say that increasing sleep duration will reduce obesity. However, we can certainly test it out. Several randomized controlled trials are doing just that (e.g., "Increasing Sleep Duration: A Novel Approach to Weight Control" Moreover, improving sleep with behavioural techniques is being investigated as a new way to improve blood-sugar levels and reduce the risk of type-2 diabetes. We eagerly await the results.

In the meantime, regardless of the outcomes of these randomized controlled trials, getting sufficient, good-quality sleep can only be helpful to our health and well-being. We need to allow sufficient time for sleep and to watch for disorders such as insomnia and sleep apnea.

Insomnia is experienced as difficulty getting to sleep or staying asleep that causes distress or impairment in functioning. About 15 per cent of the population have persistent (lasting at least one month) insomnia. Once diagnosed by your physician or psychologist, "cognitive behavioural therapy for insomnia" is an excellent treatment option.

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Obstructive sleep apnea occurs when you stop breathing (for periods of 10 seconds or more, called apneas) during rest, several times per hour. This happens when the airway collapses inward during sleep and obstructs the airflow. Sleep is disrupted as the body tries to restore airflow. You are more likely to have obstructive sleep apnea if you are overweight, you snore loudly, someone has observed you stop breathing while asleep, and if you are very sleepy during the day. If this sounds like you, see your family doctor. You may be referred for an overnight sleep study. The most common treatment is called continuous positive airway pressure (CPAP), which does wonders to maintain airflow during sleep and help you feel better during the day.

For overall health, we already know the importance of exercise, diet and sleep. We just don't know yet whether sleeping longer can help us lose weight.

Dr. Judith R. Davidson is a clinical psychologist and sleep researcher. She works with the Kingston Family Health Team and Queen's University at Kingston. She is the author of Sink into Sleep: A Step-by-Step Workbook for Reversing Insomnia. You can follow her on Facebook and on Twitter at @JudithRDavidson

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