The Washington Examiner tells us we can prevent millions of cases of obesity and thousands of strokes simply by dropping twice-a-year time changes. “Study says.” Discover magazine says so, too. The Washington Post is a little more restrained. “We’d all be a little less prone to obesity and strokes if we ditched the switch.”

Ditch the switch? Sure. We agree that it’s a pain and there’s plenty of circumstantial evidence that it harms health in a lot of subtle ways. People have more accidents and injuries when the time changes. Sleep disruption takes a toll. Even a statistical rise in heart attacks and strokes is evident.

But promising to prevent millions of cases of obesity is definitely a stretch.

A Modeling Study

What stirred up these headlines was a modeling study from two researchers at Stanford – Lara Weed and Jamie Zeitzer. PNAS, the Proceedings of the National Academy of Sciences, published it and it’s a fine piece of work.

Like any modeling exercise, it serves to illustrate a scenario of what might happen under a carefully specified set of circumstances. In this case Weed and Zeitzer set out to describe what might be the health effects that come from the interaction of circadian biology with standard time, daylight saving time, and shifts between them. Based on their careful modeling, they predict small decreases in the prevalence of stroke and obesity from eliminating time changes.

Applying these small decreases to the entire population is what fuels dramatic headlines about millions of cases of obesity. These researchers estimate that the benefits of permanent standard time would be slightly more than a permanent shift to daylight saving time would be.

But these are still just estimates. The benefits are theoretical and individually small. Not demonstrated outcomes.

Sounds Good, Falls Short

For too long, we have relied upon comforting truisms and assumptions for strategies to overcome obesity. While it’s fine with us to ditch the switch in time twice a year, promising to prevent millions of obesity cases is not such a good idea. It’s a promise that’s unlikely to come true.

It is also a distraction from more substantial efforts to prevent and treat obesity.

Click here for the study in PNAS, here, here, and here for some of the reporting on it.

Detail of Clock at Broadcasting House in London, design by Eric Gill / WikiArt