School’s out - let them lie in?

Millions of children are getting ready for a long summer break.

They’ve been working hard all term - shouldn’t you just let them sleep in?

Adolescents accumulate a ‘sleep debt’ during term time because they just can’t get to bed early enough to get the duvet-time their brains and bodies desperately need in order to cope with stress and make the grade -?Sleep Deprivation and Insomnia in Adolescence: Implications for Mental Health ,?Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing .?

Not surprisingly, the break in routine leads to a sudden delay in bed- and wake times and a steady drift over the holiday.?This large-scale study found that adolescents recovered from the sleep debt that had accumulated during the term in the first two weeks. After that, their sleep patterns got more chaotic, they took longer to fall asleep, the quality of sleep was worse when they finally drifted off and woke up more often during the night -?Electric Lighting, Adolescent Sleep and Circadian Outcomes, and Recommendations for Improving Light Health ,?Actigraphy-assessed sleep during school and vacation periods: a naturalistic study of restricted and extended sleep opportunities in adolescents .

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What’s the problem??

Sleep regularity is associated with better mental health, even in healthy adolescents -?Sleep regularity in healthy adolescents: Associations with sleep duration, sleep quality, and mental health .?Regular sleep timing is linked to better academic performance and reduced obesity scores, too.

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What’s that got to do with the lights?

There is a direct link between regular light exposure and sleep patterns, including the quality and quantity of that sleep. Those who don’t get regular light exposure get less regular sleep, compounding the problem -?Measuring light regularity: sleep regularity is associated with regularity of light exposure in adolescents .

A regular pattern of light-dark exposure is particularly important for teens as they are up to 100% more sensitive to even low levels of light in the evening than pre-adolescents and adults -?Effect of exposure duration and light spectra on nighttime melatonin suppression in adolescents and adults .

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So what can you do??

Short wavelength during the day: draw the curtains in their bedroom and encourage them to get outside or sit next to an open window in the morning before you head out to work - even if it’s to check their messages - and even if they head back to bed when you’ve left! -?Electric Lighting, Adolescent Sleep and Circadian Outcomes, and Recommendations for Improving Light Health .?

Low light levels and low stimulus in the evening.? There's a lot of talk about blue light from phones (designed to boost sales of blue-blocking glasses). But the problem is just as likely likely to be what you're doing on-line: social signals keep you awake -?Does iPhone night shift mitigate negative effects of smartphone use on sleep outcomes in emerging adults?

So simply filtering blue light or making the content less exciting are not enough to improve sleep on their own. But the two factors interact. This study found that the light emitted from screens can affect sleep quality under some conditions but this is behaviourally irrelevant in the context of normal Facebook usage -?Facebook use and sleep quality: Light interacts with socially induced alertness .?

Darkness at night. Light at night makes it harder to fall asleep and reduces the quality of sleep when they do finally nod off. Every 5-lux unit increase in light level was associated with a 7.8-min increase in sleep onset and 32% greater odds of irregular sleep onset. The effect of light at night extended to the following night with a small but significant delay in falling asleep the next day too -?Light exposure during sleep is bidirectionally associated with irregular sleep timing: The multi-ethnic study of atherosclerosis .