Social jetlag, obesity and the tyranny of the alarm clock

by Claire O’Connell

It’s 6:30am and you are in no way ready to wake up. But the alarm clock beside your bed doesn’t know that. It screams, you reluctantly surface and convince yourself to get ready for work or school. Unless of course it’s the weekend, when you don’t set the alarm and you can catch up on zzz’s.

Living against your body clock is wearying, but could it also be contributing to obesity? A new paper out in the journal Current Biology highlights a link between ‘social jetlag’ and body mass index.

Social jetlag sounds like yet another term on which to hang modern woes, but it refers to a discrepancy between your ‘circadian’ or body clock and your social clock, which can result in chronic sleep loss. And chronic sleep loss is generally not a good thing for health.

The new study asked participants, mostly in central Europe, to fill out a questionnaire about their sleep habits on work and ‘free’ days. That gave them about 65,000 entries to examine.

The analysis highlighted that sleep is profoundly influenced by social time, particularly work schedules, according to the authors. “One-third of the population represented in our database suffers from 2 hr or more of social jetlag, and 69% report at least 1 hr of social jetlag,” they write.

They also note a relationship between social jetlag and high BMI: “Over and above the impact of sleep duration, social jetlag significantly increased the probability of belonging to the group of overweight participants.”

Overall the findings suggest that living against the body clock -particularly if your body clock runs ‘late’ - may be a factor contributing to obesity.

“This is of key importance in pending discussions on the implementation of Daylight Saving Time and on work or school times, which all contribute to the amount of social jetlag accrued by an individual,” they write. “Our data suggest that improving the correspondence between biological and social clocks will contribute to the management of obesity.”

So as we mull over the many elements that feed obesity, perhaps we should throw the social need for a jarring alarm clock into the mix.

Check out the ‘video abstract’ where one of the researchers explains more about how life in the industrialised world could be playing havoc with our body clocks:
http://www.youtube.com/watch?feature=player_embedded&v=t5ylqK-aPX8

Reference:
Roenneberg et al., Social Jetlag and Obesity, Current Biology (2012),
doi:10.1016/j.cub.2012.03.038