Sleeping badly could be driving weight gain, scientists fear, after finding that people who slept just six hours a night had waist measurements an inch greater than those who get nine hours.
The results strengthen the evidence that insufficient sleep could contribute to the development of metabolic diseases such as diabetes.
The study by the University of Leeds involved 1,615 adults who reported how long they slept and kept records of food intake. It also measured other indicators of overall metabolic health such as blood pressure, blood cholesterol, blood sugar, and thyroid function as well as weight and waist circumference recorded.
Those who slept for six hours or less a night had waists that were on average 1.1 inches (3cm) larger than those who slept for nine hours.
Shorter sleep was also linked to reduced levels of good cholesterol which helps remove fat from the body and protects against conditions like heart disease.
Dr Greg Potter, a researcher in metabolism at Leeds University, said: “The number of people with obesity worldwide has more than doubled since 1980.
“Obesity contributes to the development of many diseases, most notably type 2 diabetes. Understanding why people gain weight has crucial implications for public health.”
Crucially, the study did not find any relationship between shortened sleep and a less healthy diet – a fact that surprised the researchers.
Other studies have suggested that shortened sleep can lead to poor dietary choices. But the new research suggests that it is the sleep itself which is driving the effect.
Dr Laura Hardie, the study's senior investigator, added: “Because we found that adults who reported sleeping less than their peers were more likely to be overweight or obese, our findings highlight the importance of getting enough sleep.
“How much sleep we need differs between people, but the current consensus is that seven to nine hours is best for most adults.”
The findings add to the growing body of evidence showing just how important a good night's sleep is to health.
The research was reported in the journal PLOS ONE.