Magazines, newspapers and the internet are awash with claims that lack of shut-eye piles on the pounds. And at first sight it seems pretty cut and dried. As we’ve become collectively more sleep-deprived our weight has soared in parallel. Numerous studies following people over several years have linked short sleep (usually less than seven hours) to increased weight – at least in children, teenagers and younger adults (the link is weaker in over 55s).
In principle there are good reasons why lack of sleep could push up the number on your scales. If you’re sleep-deprived it’s easier to slump on the sofa than to get out to the gym or take a healthy walk, decreasing the ‘calories out’ side of the weight balance equation. There’s also evidence that even a couple of days of lost sleep (four hours in most studies) upsets the balance of appetite-regulating hormones such as leptin, which quells appetite, and ghrelin, which stimulates it, making us hungrier – especially for comforting high-carb foods. It’s even speculated that overeating when you’re short of zzzz is your body’s way of trying to restore sleep, given that higher food intake promotes sleep. An intriguing suggestion. Recent studies meanwhile suggest that sleep loss may disrupt how our bodies deal with glucose and insulin, leading us to pile on weight, especially around the waist, increasing the risk of diabetes.
Case proven then? Erm, not quite. Unfortunately much existing research is flawed. For a start sleep is just one of a raft of behaviours examined in many studies, making it virtually impossible to tease out whether it’s lack of sleep or something else that is the culprit in weight gain. What’s more, most studies use tick-box questionnaires to assess participants’ sleeping habits – a notoriously unreliable way to measure anything, let alone sleep.
Also many studies ask only about night time sleep – not very helpful in people who nap or work shifts. In fact one study found that obese participants were more likely to take day time naps meaning that while short night time sleep was linked with obesity there was no link with overall length of sleep.
Just to confuse matters further most studies have been performed on young, normal-weight, healthy men. We don’t really know what the effects of lack of sleep are on women, older people or those who are already overweight.
Even studies of appetite-regulating hormones don’t all point in the same direction – with some showing an increase in hunger hormones and others not. And is short sleep a cause or effect? Overweight increases the risk of sleep-stealing conditions like osteoarthritis, heartburn, asthma and heart failure. It also puts you at risk of obstructive sleep apnoea (OSA), a major cause of snoring, when sleep is interrupted by multiple pauses in breathing.
Frustratingly, there are few clinical trials looking at the effects of sleep deprivation on weight or, more to the point, on whether longer sleep can aid weight loss, which could settle the matter one way or the other.
So it seems that, despite what you might read, it’s too early to blame your sleeping habits for burgeoning weight. We’ll be keeping a look out for the latest research on this fascinating question, so watch this space.
Image © GiZGRAPHICS – Fotolia.com. Patsy Westcott, co-founder of this blog, is a health writer and nutritionist.