Obesity

Nutritional Pearls: Sleep Time and Obesity

  • The Research

    In 2006, we shared a study that reviewed the relationship between sleep time and body mass index, which found that those who slept less than 6 hours per night were far more likely to be clinically obese than those who slept 9 hours or more.

    The study population included almost 1000 people in rural Iowa. Earlier this year, a similar study was published in JAMA Network Open,1 but it is far more thorough. It also looks at what time people went to bed, when they got up, and whether they slept during the day.

    For this study, an international team of researchers analyzed data gathered for the Prospective Urban Rural Epidemiology (PURE) study, which was designed to assess the global burden of cardiovascular diseases and risk factors. It includes participants from 60 locations in 26 countries of different income levels worldwide, from the United States to Poland to Tanzania.

    More than 136,000 people aged 35 to 70 years were extensively surveyed regarding their diet, physical activity, health, habits, when they typically went to bed for the evening, when they usually woke up in the morning, and if/how much they napped in the afternoon.

    Each participant was weighed, and their height was measured to calculate their body mass index (BMI). In addition, their waist and hips were measured for waist-to-hip ratio (WHR).

    The authors note that overall, the average nighttime sleep duration is just less than 8 hours (7.8), with those from higher-income countries going to bed (on average) just before 11pm local time. The average bedtime for those in middle-income countries was 33 minutes earlier and 45 minutes earlier in low-income countries.

    The Results

    After considering a truly impressive array of factors, including caloric intake and physical activity, the authors found that, compared with a bedtime of 8pm to 10pm, those who went to bed later were at a higher risk of both general obesity (a higher BMI) and abdominal obesity (a poor WHR)—a risk that increased the later an individual went to bed. Those who went to bed between 10pm and 6am were 20% more likely to have general or abdominal obesity, and those who went to bed after 2am were about 35% more likely to have general or abdominal obesity.

    The results for sleep duration are similar: compared with those who slept 7 to 8 hours per night, those who slept less than 5 hours were 27% more likely to be generally obese and 16% more likely to be abdominally obese.

    What about napping? Only 40% of the participants said they napped regularly. Compared with those who did not nap at all, those who napped for less than 1 hour per day were 15% more likely to have general obesity and 19% more likely to have abdominal obesity. Napping more than 1 hour brought the risk even higher to 22% more likely to have general obesity and 39% more likely to have abdominal obesity.

    What’s the Take Home?

    The authors note that the current guidelines from the American Academy of Sleep Medicine and Sleep Research Society recommend at least 7 hours per night for general health, but there is no recommendation for when you should go to bed. If you're working on your weight, make sure you're getting at least 6 hours of sleep per night, and try to go to bed before 10pm.

    Reference:

    1. Tse LA, Wang C, Rangarajan S, et al. Timing and length of nocturnal sleep and daytime napping and associations with obesity types in high-, middle-, and low-income countries. JAMA Netw Open. 2021;4(6):e2113775. doi:10.1001/jamanetworkopen

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