The Nap

Sleep More, Weigh Less? Actually, Probably, Yes

Sleep, stress, and obesity are clearly related. But the relationship is complicated and causality is tough to unravel. Stress interferes with sleep. So does obesity. And then, too, both stress and too little sleep can contribute to obesity. So if you sleep more, will you weight less? A natural experiment in Korea tells us for adolescents, this is likely true.

It’s a good example of how researchers can find evidence for cause and effect from natural experiments.

A 10 PM Curfew for High School Students

In 2010, the South Korean government proposed a 10 pm curfew to protect the sleep of adolescents. So three regions of the country adopted it for high school students. Thus, Young Kyung Do saw an opportunity for a natural experiment. He used a nationally representative sample of adolescents from a youth risk behavior survey. Government policy handed him a random assignment of adolescents to a sleep intervention.

He found that the policy change in those regions did result in more sleep for youth in his sample. And he found that the increased sleep was associated with a reduction in BMI and a four percent reduction in the risk of overweight or obesity.

Note that these are not huge effects. But they are effects that likely reflect causality at a population level. More important, they corroborate an extensive body of observational research linking less sleep to higher body weight.

A Tangled Relationship

In this analysis, many factors are in play. Extra sleep can have an effect on eating patterns, physical activity, and stress. The paper used an instrumental variables analysis to provide insight on how these factors interact. Professor Do admits that certainty is not possible. Nonetheless, he concludes that the main effect of the curfew on BMI most likely came from more sleep.

In a recent review, Nina Geiker and colleagues tell us that stress, like sleep, has an important role here:

Not only do the adverse effects of stress influence sleep patterns, food intake, weight gain, abdominal obesity and the effects of weight loss interventions but evidence also suggests that improving nutritional status and sleeping patterns may reduce the severity of stress and other mental disorders.

Understanding the cause and effect relationships with obesity tells us that addressing obesity at a population level may require more than food policy changes alone. The Korean government had no intent to reduce obesity when it implemented a curfew for high school students. But that’s what happened.

We need to be prepared for serendipity and surprises. Presumptions don’t always prove to be true.

Click here for the study of the Korean curfew and here for the review by Geiker et al.

The Nap, painting by Gustave Caillebotte / WikiArt

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November 23, 2019

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