Teens are getting less sleep these days — and it could make them more likely to have heart disease as adults.

Over the past 20 years, the amount of sleep that teens get has dropped significantly. Only about half of them regularly get more than seven hours of sleep, with older teens sleeping less than younger ones — which, given that the recommended amount is eight to 10 hours, is bad news.

This is bad news for all sorts of reasons. Our bodies need sleep. When we get less sleep, not only are we cranky, we are less able to learn new information, our reaction times are longer, we may have behavioral changes or mental health problems — and it affects our health.

In a study just published in the journal Pediatrics, researchers looked at the sleeping habits of 829 adolescents between the ages of 12 and 16, with a mean age of 13. They found that a third of them slept less than seven hours every night, and nearly half of them were fully asleep for less than 85% of that nightly sleep time.

But here’s where it gets worrisome. The researchers found that those who got less sleep were more likely to have a high “metabolic risk score.” They were more likely to have belly fat, high blood pressure, and abnormal blood lipids, as well as insulin resistance, something that increases the risk of diabetes.

So not only are sleep-deprived teens more likely to do poorly in school, be depressed, and get into car crashes, they are also more likely to have heart disease when they are adults.

While homework, other activities, and early school start times certainly contribute to teens getting less sleep, the biggest culprit seems to be electronic devices. The blue light emitted from them can wake up the brain, making it harder to fall asleep (the “Night Shift” setting on the phones does not entirely take care of this problem) — but more commonly, teens simply stay up late using them.

This demands action. We can’t just sit back and say that “teens will be teens” when it comes to sleep — not when their future health is at risk.

Here’s what parents can do:

• Make a rule that electronic devices get turned off an hour before their teen needs to fall asleep (meaning eight to 10 hours before they need to wake up). It’s best if they are charged outside the bedroom, so that there is no temptation to respond to alerts. A second choice is to have phones on “Do Not Disturb,” which quiets all alerts except alarms (although buying an alarm clock is a viable alternative that many people forget about these days).
• Enforce this rule.
• Prioritize sleep. Sit with your teen and look at how their time is spent, and map out the day so that they can get to bed on time. If their homework and other activities make it impossible to get at least eight hours of sleep, then something needs to give. Physical and mental health needs to be more important than whatever it is they are doing instead of sleeping.
• Support community efforts to have later high school start times. Teens are biologically wired to fall asleep late and sleep late, and when we make them get up really early for school, we are only making everything worse.

We want our kids to have a good future. That’s why we talk to them about avoiding tobacco, drugs, and alcohol, about working hard in school and staying out of trouble. And it’s why we need to talk to them about sleep.

Follow me on Twitter @drClaire

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