Researchers find that both the quantity and quality of sleep, the amount of time spent sleeping and the percentage of sleep that is undisturbed in young adolescents have significant effects on aspects of cardiovascular health such as blood pressure, cholesterol levels, and abdominal fat deposition. 

While many studies have associated shorter sleep duration with increased obesity levels in children, few have examined effects on other risk factors such as blood pressure, blood lipids and examined associations of sleep quality with these outcomes.

The current study reports result from 829 now-adolescent study participants who, along with an in-person study visit, had both their nighttime sleep and daily physical activity measured over 7 to 10 days by actigraphy, which records physical motion by a device worn on the wrist. The participants, who averaged around 13 years in age, also completed written sleep logs. 

Time Spent In Night

In addition to sleep duration the amount of time spent asleep during the night actigraphy also measured sleep efficiency, the percentage of time during the overnight sleep period spent asleep, an indication of the quality and continuity of sleep.

Results showed that the average sleep duration for all participants was 441 minutes or 7.35 hours per day; and only 2.2% met or exceeded the recommended average sleep duration for their age group, 9 hours per day for ages 11 to 13 and 8 hours per day for those 14 to 17.  Sleep duration of fewer than 7 hours was found in 31% of participants, and more than 58% had sleep efficiency less than the 85% that is considered sufficient for adults.

Both shorter sleep duration and lower sleep efficiency were associated with increased levels of overall and abdominal fat deposition associations that persisted after adjustments for physical activity, television viewing, and consumption of fast foods or sweetened beverages. 

Longer sleep duration and higher efficiency were associated with reductions in cardiometabolic risk based on factors such as smaller waist circumference, lower systolic blood pressure and higher HDL cholesterol levels. Most of those associations also persisted after adjusting for the factors noted above.

Quantity And Quality Of Sleep

Sleep quantity and quality are pillars of health alongside diet and physical activity. Pediatricians should be aware that poor sleep quality frequent awakenings and not the just insufficient duration of sleep are associated with increased cardiometabolic risk. 

While several trials have tried to extend the duration of sleep, few have targeted sleep efficiency and other aspects of sleep quality.  They know that exercise improves sleep efficiency in adults and that screen time decreases it in children, so preventive measures should target those and other factors such as stress, noise, and caffeine consumption.

Circadian Clock

Sleep has many dimensions beyond its quantity and quality that may influence cardiometabolic health, including the relationship of sleep timing to other daily activities and whether an individual's circadian clock, the internal sleep/wake schedule, is synchronized with the rhythms of social activities. 

Those may be particularly important in adolescents who may have high academic demands or naturally prefer to be active in the evening but need to get up early for school and will be a focus of our upcoming research.