People who find it difficult to get out of bed at the weekends are more likely to suffer from chronic health problems such as obesity and diabetes compared to individuals who are up with the lark even when they do not have to go to work, a study has found.
Scientists said that people with “social jet-leg” – when sleeping patterns differ significantly between work days and rest days – may suffer from a chronic metabolic disturbance that causes them to pile on the pounds and to develop diabetes and other health problems.
The researchers found an association between social jet-leg and body fat when they analysed the sleeping patterns and weight of more than 800 people who have been followed for many years as part of the Dunedin Longitudinal Study in New Zealand.
Although they cannot say that social jet-leg causes obesity, the scientists believe that the link supports the idea that people whose body clocks are perpetually out of synch with their work patterns are putting their metabolism under strain, which manifests itself as obesity and other chronic disorders.
“Obesity, as with many complex health problems, is the result of a number of factors and our study suggests that social jet-lag is one of the factors that needs to be taken into account,” said Michael Parson of the Mammalian Genetics Unit at the Medical Research Council in Harwell.
“Social jet-lag is an under researched but potentially key contributor to why living against our internal body clock has an impact on our health,” said Dr Parson, who is the lead author of the study published in the International Journal of Obesity.
“Our research confirms findings from a previous that connected people with more severe social jet-lag to increases in self-reported body mass index [body fat], but this is the first study to suggest this difference in sleeping times an also increase the risk for obesity-related disease,” he said.
The body’s internal clock runs on a “circadian rhythm” of about 24 hours but some people are considered “owls”, being more alert and active in the evening, while others are “larks”, being at their best in the morning.
Although many people tend to sleep in at the weekends when they do not have to go to work, the tendency for social “jet lag” with their work-day routine can differ markedly between individuals. It was this difference between week-day and week-end sleep patterns that the study analysed, Dr Parson said.
“We found that for every two hours of social jet-lag we saw an average increase of about 2.5kg (5lbs) in fat mass among those individuals. We think this relates to the daily rhythm regulating the expression of about 10 per of the body’s genes, many of which are involved in fat metabolism,” he said.
“It’s compatible with the hypothesis. As little as 2 hours of social jet-lag can increase the risk of health biomarkers such as obesity and diabetes,” he explained.
The researchers suggest that policies on working hours, such as the introduction of flexi-time, could be introduced to reflect the possible health risk for people who have to work against their body clocks.
Terrie Moffitt, a co-author of the study, said: “Further research that determines this association could help to inform obesity prevention by influencing policies and practices that contribute to social jet-lag, such as work schedules and daylight savings.”