About half of all Americans report feeling sleepy during the day between three and seven days each week, and 35.2 percent of all adults report sleeping 7 hours or less each night. Over the past decade, studies have begun to emerge regarding the possible link between shorter hours of sleep and weight gain or obesity.
A systematic review led by researchers Sanjay Patel at University Hospitals Case Medical Center and Case Western Reserve University in Cleveland, Ohio, and Frank Hu at the Harvard School of Public Health, sought to analyze the available evidence.
Studies spanning five continents
The U.S. researchers poured through a total of 36 articles between 1966 and 2006. Unfortunately, a meta-analysis of the data was unable to be performed due to the differences in study designs, measures of association between variables, and definitions of short sleep duration.
In children, there appeared to be a positive association between weight and sleep duration based on eleven studies. In 8,274 Japanese children aged 6 and 7, the odds ratios (ORs) for obesity were 1.49, 1.89, and 2.89 for sleep durations of 9 to 10, 8 to 9, or <8 hours compared to children sleeping at least 10 hours.
An odds ratio measures the strength of the association between an event and an exposure, and is a ratio of the “odds of the event occurring in an exposed group versus the odds of the event occurring in a non-exposed group.”
Another study of 4,511 children aged 7 to 9 in Portugal had similar results, with ORs for obesity of 2.27 and 2.56 for sleep durations of 9 to 10 and 8 hours compared to sleep durations of 11 or more hours.
In adolescents aged 11 to 16, a study conducted by Gupta et al. using wrist actigraphy, or a device similar to a wristwatch, showed that the odds of obesity increased “five-fold for every hour reduction in sleep duration.”
Likewise, a study by Benefice et al. showed that in 40 Senegalese girls aged 13 to 14, sleep duration was 6.85 minutes less for every 1 kilogram per square meter increase in BMI (body mass index).
Overall, the included studies spanned five continents, with no obvious differences observed on the basis of ethnicity or race. In the adult population, cross-sectional data “suggest short sleepers are heavier though the findings are much less consistent than the pediatric data.”
Many mechanisms have been proposed regarding the relationship between sleep and weight gain, such as the idea that chronic partial sleep deprivation “causes feelings of fatigue which lead to reduced physical activity,” or how less sleep can have “neurohormonal effects that increase caloric intake.”
Increasing prevalence of obesity
According to the Centers for Disease Control and Prevention (CDC), the prevalence of obesity was 41.9 percent between 2017 and March 2020. Among those aged 2 to 19 years old, obesity was present in 19.7 percent.
However, among adults aged 20 and over, “The age-adjusted prevalence of obesity was 41.9 percent, severe obesity was 9.2 percent, and diabetes was 14.8 percent.”
In contrast, just two decades ago from 1999 to 2000, the prevalence of obesity was 30.5 percent and the prevalence of severe obesity was 4.7 percent. Obesity increases the risk of developing several conditions, including heart disease, stroke, diabetes, and cancers.
In the U.S., the financial burden of obesity has reached $173 billion, with the average medical costs for obese adults estimated to be $1,861 more than the medical costs for adults with healthy weights.
Approximately 35.2 percent of adults sleep less than 7 hours per night, according to 2014 CDC data. Interestingly, when separating by age, adults aged 45 to 54 were most likely to sleep less than 7 hours, coming in at 39.0 percent, compared to just 26.3 percent in those 65 years and older.
Short sleep was also found to be more common in those who were obese (body mass index or BMI of 30 or greater), physically inactive, current smokers, and excessive alcohol drinkers.