With so many things competing for teenager's attention late at night homework their favorite TV shows unwinding from a part-time job and of course catching up on their friend's latest gossip on social media getting teens to go to bed early is usually a losing battle. If only they knew what a growing body of research is beginning to show: insufficient sleep during teen years can set the stage for insulin resistance and obesity in adulthood. Little do these teens know that in terms of establishing good habits early on that can lead to a lifetime of better health hitting the sack may be just as important as hitting the gym.
A longitudinal study that followed over 10000 adolescents (mean age 16) through young adulthood (mean age 21) concluded that getting less than 6 hours of sleep a night during adolescence is associated with obesity later on in life. A systematic review looking at short sleep duration and weight gain confirmed a strong and consistent association between short sleep duration and future weight gain. A similar meta-analysis that also looked for links between the amount of sleep and future obesity found a striking odds ratio of 1.89 (1.46 to 2.43; P < 0.0001).
The main mechanism that is likely fueling future weight gain as a result of reduced sleep time is insulin resistance. It is well recognized that insufficient sleep both acute and chronic is associated with insulin resistance and the resultant impaired glucose tolerance. Adolescents getting less sleep have significantly higher markers for insulin resistance than those that sleep more. Those who get about 5 hours of sleep show increased insulin resistance (via HOMA-IR score) compared to those who sleep an average of 7.75 hours. Interestingly however subjects sleeping closer to 10.5 hours also have elevated HOMA-IR scores leading to a U-shaped curve between sleep duration and insulin resistance. A likely explanation for this trend is that the longer sleep may be a result of pre-existing metabolic disturbances rather than their cause.
Reduced amounts of sleep also result in a downregulation of the satiety hormone leptin leading to increased hunger and food intake. Sleep deprivation has been shown to significantly decrease leptin levels increase levels of the antagonistic hormone ghrelin (which stimulates appetite) and increase hunger in general - more specifically it boosts hunger for high-carbohydrate foods.
The combination of being hungry and sleep-deprived is a double-whammy when it comes to food selection. Teenagers (or people of any age for that matter) are more likely to make poor food choices and grab processed convenience foods which are high in sugar and harmful fats in order to get a quick pick-me-up rather than opting for whole natural foods that take more time to prepare and are less associated with an energy boost.
Beyond sleep duration sleep quality may also play a role in weight management and overall health. They are connected; lower total duration of sleep means less time in each stage of sleep. Sleep and circadian rhythms are intimately connected to endocrine function with sleep duration and quality affecting hormone pulsing and vice-versa. Higher amounts of delta-wave activity during sleep are associated with pulses of prolactin and muscle-boosting growth hormone while lower delta-wave activity is associated with increased thyroid stimulating hormone (TSH) and cortisol. Specific sleep stages determine nighttime hormonal release and glucose control. During a deep stage of sleep called slow wave sleep (SWS) sympathetic nervous activity is decreased and parasympathetic nervous activity is increased compared to waking hours. SWS is linked to elevations in growth hormone and the inhibition of pituitary-adrenal activity. Because of this researchers believe SWS likely plays a major role in whole-body glucose regulation. Think of it as sleep being a surefire way to calm down. When teenagers are sleeping they're not stressed out about the math test later in the week or who's asking whom to the prom. For some kids long deep sleep might be the only chance their brains and their hormones get to rest.
Of course getting sufficient sleep is easier said than done. The CDC recommends that teenagers get 9-10 hours of sleep a night. With an estimated wakeup time of 6:30a.m. in order to get ready for school teens would need to be in bed by 9:30p.m.a time when many of them are just coming home from after-school jobs or remembering at the last minute the big test the next day that they forgot to study for.
Still for a practice that can influence long-term health body weight and quality of life teenagers should turn off their screens and devices and turn in for the night preferably earlier than they'd like to.
For related information on sleep please listen to our Sept 28 2011 Clinical Rounds call on Sleep Disorders with David Brown Ph.D.