An hour’s extra sleep could skim 1cm off your waist
Scientists add weight to the theory that sleep and waist circumference are linked.
A good night's sleep might impact more than your mood the following day: it is also linked to your waistline, regardless of your diet, according to research from the University of Leeds.
A team lead by Dr. Laura Hardie investigated whether there is a link between sleep duration, diet, waist circumference and other indicators of health, such as cholesterol levels.
Studying over 1,600 people, they found that good sleepers had better indicators of health, were lighter and had smaller waistlines despite, to their great surprise, there being no association between sleep duration and diet.
Hardie and her colleagues originally set out to test the hypothesis that poor diet is behind a well-known link between sleep duration and obesity, using data from the “National Diet and Nutrition Survey”.
A population, fairly representative of British adults, was asked to report their sleeping habits and make a food diary for 3-4 days, and a selection of these people had their health levels tested.
Using this dataset, the scientists then performed complicated statistical analysis to look for correlations between different parameters, such as sleep duration and waist size.
They found that individuals who get, on average, about 6 hours sleep have waistlines that are 4cm larger than those who get about 8.5 hours sleep.
When they adjusted their algorithm to account for variables known to affect weight levels, and waist circumference; such as age, gender and socioeconomic status, they still found that every hour of sleep lost accounts for an average extra 0.9cm around the middle.
These findings are consistent with other studies linking obesity and poor sleep. Broadly speaking, scientists believe there are two main reasons behind this link.
Some believe that less sleep impairs the body's ability to respond to glucose, or sugar. Similar problems with glucose are also occur in obesity and diabetes. Although other studies back this, the work by Hardie doesn’t provide enough evidence to support or refute this hypothesis.
The other major theory is the poor sleep decreases the levels of the hormone leptin, which makes us feel full and simultaneously increases the releases of the hormone that makes us feel hungry, called ghrelin. The changes to our hormones leave poor sleepers with increased appetites.
Hardie and her colleagues were testing this hypothesis, albeit indirectly. They were looking to see if poor sleep causes individuals to make bad decisions concerning their diet, with the diet responsible for the weight gain.
Unexpectedly, they found no link between sleep duration and diet. However, their study, published in PLOS One, was actually quite small compared to other population studies, such as UK Biobank, which is collecting information on the long term health of half a million people.
The authors also asked participants to generate food diaries for 3-4 days. These diaries were self-reported. It is possible that participants made mistakes or deliberately under-reported their intake. If this happened, the scientists wouldn't be able to properly detect a relationship between diet and sleep without the correct information.
Even without a strong link between sleep and diet, Hardie’s work hammers home just how big an impact sleep has on our body sizes. This creates a compelling argument to add good sleep to diet and exercise for a trio of tools for optimal health.