(CNN) Teenagers engaged in sports and exercise have lower risks of using opioids without a doctor's order, according to a study published Monday in the journal Pediatrics.
Researchers at the University of Michigan looked at data from more than 191,000 eighth- and 10th-graders who participated in the Monitoring the Future survey from 1997 to 2014.
Among the respondents, 53.3% reported sports and exercise participation almost every day ("highly involved"), 38.8% reported it once a week at most ("moderately involved"), and 7.9% had not participated in sports and exercise in the past year.
The students were also asked about their opioid use. Overall, those who were highly and moderately involved in sports and exercise were less likely to use prescription opioids without a doctor's prescription or to use heroin than those who reported no involvement.
Nonmedical use of prescription drugs dropped from 8.8% in 1997 to 4.4% in 2014 among the highly involved athletes, according to the study. Heroin use among these highly active teens showed a similar decrease, from 1.8% in 1997 to 0.8% in 2014.
Athletes were also found to be no more likely to misuse prescription opioids before using heroin than their inactive peers.
"The unfortunate pattern of prescription painkiller misuse to heroin use was not something that was more likely to occur among athletes either moderately or highly involved in sports," said Philip Veliz, lead author of the study and an assistant research professor at the University of Michigan.
Opioid use among adolescents is worrisome because it could lead to long-term opioid use and abuse in adulthood. Research has showed that high schoolers who use opioids with a prescription are 33% more likely to misuse opioids after graduation.
Teenage athletes are thought to be a population particularly vulnerable to opioid abuse. Veliz's previous studies have showed that young athletes who participated in high-contact sports, such as football and wrestling, were actually at greater risk of abusing opioid painkillers and heroin.
He suspected that it could be the result of greater likelihood of injury or a greater chance of getting diverted opioids from teammates. These teenagers are more likely to be prescribed opioid painkillers or to self-medicate to recover from injuries and cope with other problems, according to Veliz.
The current study, on the contrary, found sports participation and exercise to be a "protective factor" against prescription drug misuse and heroin use.
Veliz said sports involvement might have physical and social benefits that keep teens from opioid use.
According to Veliz, the majority of teens who play sports or exercise do not necessarily participate in high-injury sports. And because they are physically active, they may be strengthening their bodies to prevent injuries.
Young athletes also might be monitored by adults "around the clock" and are less likely to step out of the line, especially after school and during the summer, he said.
"There's a social control aspect," Veliz said. "It's good for your social well-being because you're involved with an activity with other like-minded youth who want to better themselves."
Veliz said the positive effects of sports and exercise may be carried through adulthood, although there is currently not enough research that considers associations between college athletics and opioid abuse.
The results of the current study point to decreases in heroin use and prescription opioid misuse across athletes and non-athletes.
Veliz said he was surprised to see such declines. "I was expecting a positive increase given the recent trends," he said, referring to the increase in prescription opioid use among adults, starting in the mid-1990s, and a rise in heroin abuse.
Opioid abuse among adolescents, however, shows a distinct trend. Both the Centers for Disease Control and Prevention's 2015 Youth Risk Behavior Survey and the latest National Institute on Drug Abuse Monitoring the Future survey found significant decreases in both prescription drug and heroin use among youth.
But another researcher said the study didn't consider the right question about teen athletes and opioids.
Dr. Andrew Kolodny, chief medical officer of Phoenix House, a substance abuse treatment program, said the United States is experiencing an epidemic of opioid addiction, not a recreational opioid use problem. Medical use of opioids, in addition to nonmedical use, is a risk factor for opioid addiction.
"They studied the wrong problem. ... The issue with young athletes is medical use, not nonmedical use," said Kolodny, who was not involved in the new study. "Young athletes are becoming addicted to opioids through medical treatments for injuries. And playing sports may actually increase risks of addiction if injuries are treated with opioids."
Veliz said the scope of the current study was limited by the data available. The researchers were able to find out only whether teens are using prescription opioids without doctors' prescriptions and the frequency of their sports and exercise participation, he said.
The findings of the current study do not mean that coaches, parents and physicians need not think about opioid abuse among teens, Veliz cautioned. Athletes involved in high-injury sports, such as football, ice hockey, lacrosse and wrestling, might still try to hide pain. They require close monitoring of their prescription painkiller use.
Parents may encourage their children to play sports but should watch out for warning signs such as depression and continued use of medications after their injuries.
Moving forward, Veliz hopes to study which types of sports are particularly linked to higher risks of prescription painkiller and heroin abuse.