How Do Sleep Quality, Physical Activity Impact Teens' Metabolic Health?

Reduced physical activity and greater nightly variation in sleep duration are associated with less favorable metabolic profiles in adolescents, including higher fat accumulation and higher insulin levels, according to a study published in PLoS One.

Between 1975 and 2016, the prevalence of overweight individuals nearly tripled worldwide, as over 39% of adults and 18% of children and adolescents were considered overweight or obese in 2016. According to researchers, “Greater total body and central adiposity is associated with increased risk of cardio-metabolic comorbidities, such as hypertension and diabetes."

However, both sleep and physical activity are modifiable behaviors that, when well managed, can reduce the risk of obesity, weight gain, and metabolic health problems.

In a cross-sectional study of 252 Icelandic adolescents with a mean (SD) age of 15.8 (.3 years), researchers analyzed the association between metabolic risk factors and objectively measured school day physical activity and sleep characteristics. Of the 252 study participants, 146 were female.

Participants wore accelerometers on their wrists to measure 1 school week of free-living sleep and physical activity. Analyses were focused on school days (Monday-Friday) and nights (Sunday-Thursday) and did not include data for weekends or holidays.

Sleep duration, quality, and timing were used to evaluate sleep behavior. To correct for skewed distribution, sleep and bedtime variability were log-transformed prior to regression analyses, the authors note. Metabolic risk factors including body mass index (BMI), waist circumference, total body and trunk fat percentage, resting blood pressure, and fasting glucose and insulin levels were also measured.

The researchers found that the median (interquartile range [IQR]) night-to-night variations in bedtime and sleep duration were 0.75 (IQR, 0.55) hours and 0.64 (IQR. 0.53) hours, respectively.

In addition, data showed:

• A positive association between nightly variability of sleep duration and both total body and trunk fat percentages
• A negative association between physical activity and trunk fat percentage and fasting insulin levels
• When average sleep duration, wake after sleep onset, and physical activity were accounted for, negative associations between physical activity and trunk fat percentage and fasting insulin levels remained significant. Standardized β values presented as: —0.114 (95% CI, 0.218 to –0.010) and –0.203 (95% CI, –0.332 to –0.074), respectively
• Bedtime variability was positively associated with BMI (β = 0.140; 95% CI, 0.014-0.267), waist circumference (β = 0.137; 95% CI, 0.016-0.257]), total body fat percentage (β = 0.060; 95% CI, 0.070-0.250), and total trunk fat percentage (β = 0.161; 95% CI, 0.060-0.263)

The investigators’ combined regression model indicated that a 30-minute increase in variability of nightly sleep would lead to a 1.1% increase in trunk fat and an 0.9% increase in total body fat. Furthermore, a participant in the upper range of bedtime variability “(the 19th percentile, with variability of 1.39 hours over school week) could be expected to have 3.4 percentage points higher body fat than those in the lower range of the cohort (the 10th percentile, with variability of 0.27 hours over the school week).”

Although greater nightly variation in sleep duration and bedtime were associated with less favorable indicators of metabolic health, “surprisingly, neither mean bedtime nor average sleep duration on school nights was associated with any of the cardiometabolic risk factors measured in our study,” the researchers said.

Due to the sample’s racial and ethnic homogeneous makeup, they note generalizability may be limited.

Reference

Rognvaldsdottir V, Brychta RJ, Hrafnkelsdottir SM, et al. Less physical activity and more varied and disrupted sleep is associated with a less favorable metabolic profile in adolescents [published online May 15, 2020]. PLoS One. doi:10.1371/journal.pone.0229114