Teenagers who don't get enough sleep are more likely to have conditions that could affect their heart health down the road, a new report finds.
Researchers found that of 4,100 teenagers they studied, the one-third with the poorest sleep quality were more likely to be overweight or have unhealthy blood pressure or cholesterol levels.
Poor sleep included problems falling asleep or staying asleep, nighttime "restlessness" and bad dreams, among other things.
The findings do not prove that the sleep problems are to blame, according to senior researcher Dr. Brian C. McCrindle, of the Hospital for Sick Children in Toronto, Canada.
"It's hard to get at the causal pathway," he said in an interview.
That is, sleep problems are often connected to a range of less-than-ideal lifestyle habits. People who get little sleep tend to get less exercise, spend more time in front of the TV and eat a poorer diet than better-rested folks.
And that was true of sleep-deprived teens in this study.
But even when the researchers factored those things in, poor sleep was still linked to a higher rate of potential heart risks. So it's possible that disturbed sleep, itself, plays a role.
And even if the link is indirect - daytime drowsiness keeping kids inactive, for example - it would be important for teens to catch enough Z's.
"When people think about cardiovascular risk, sleep doesn't usually come up," McCrindle said. "These findings give some more evidence that sleep is one of the things people should think about."
The study, which appears in the Canadian Medical Association Journal, included 4,100 Ontario teenagers who answered questions on their sleep quality. All of the kids were healthy, but the one-third with the worst sleep scores showed signs of potential heart trouble down the road.
Overall, 48 percent were either overweight or had elevated blood pressure or "bad" cholesterol. That compared with 39 percent of kids who were more well-rested.
Then the researchers weighed other factors - like kids' reports on their diet, exercise and TV habits. It turned out that the one-third of teens with the worst sleep quality were 43 percent more likely to have heart risk factors than the third with the best sleep quality.
And while the kids' hearts were healthy, that could change later in life.
"These risk factors tend to track into adulthood," McCrindle said. "And they tend to get worse."
Some studies in adults have linked poor sleep to heart disease and diabetes. Again, researchers don't know the precise reason. But one theory is that getting too little sleep could have negative effects on certain hormones - including ones that regulate appetite and fat metabolism.
People who are awake into the wee hours may also have more chances for snacking, and less energy for exercise the next day.
"I think the importance of sleep hygiene cannot be overemphasized," said Dr. Indra Narang, the lead researcher on the study.
"In general, we recommend that teenagers get 8 to 9 hours of sleep each night," Narang said. But in reality, she noted, studies suggest that half of teenagers get fewer than 7 hours of sleep on weeknights.
Weekends are a different story, since kids often take the chance to sleep in. But that doesn't make up for late nights during the week, Narang noted.
"You don't repay your sleep debt by sleeping in on the weekends," she said.
Narang and McCrindle said parents should encourage their kids to keep a consistent sleep schedule on all days of the week. And to help them do that, get the "stimulants" out of their bedrooms - TVs, computers and cell phones.
Cutting down on caffeinated drinks during the day can also help. Some of the biggest culprits, like energy drinks and coffee-based concoctions, are very popular with teenagers, McCrindle noted.