Getting teenagers off of the couch can be difficult, but the benefits are undeniable.

Let’s perform a little parental thought experiment. Your daughter (or son) is in her senior year of high school, headed for the exit, when she’s told she must perform 30 hours of community service before graduation. How does the scene play out? A bit of drama, perhaps some eye rolling and door slamming. After you threaten to revoke her car privileges, she signs up to volunteer at the local elementary school. Once a week, she spends an hour reading to youngsters, helping out with homework, leading playground games, and organizing arts and crafts. In the end, she survives. Maybe she even has fun.

In fact, say researchers, it gets better. A controlled, randomized study of 100 Canadian high school students reveals that those assigned to three months of weekly volunteer work came out of the experience happier—and healthier—than their classmates.

Twelfth graders at an urban British Columbia school were recruited to volunteer in an after-school tutoring program; half were randomly assigned to begin immediately, while the other half were assigned to begin the following semester. All the students underwent personality assessments, designed to gauge their negative affect, self-esteem, and prosocial skills (e.g. empathy and altruism). They also submitted blood samples, with which researchers measured their levels of cholesterol and inflammatory markers (associated with obesity, heart disease, and type-2 diabetes). At the end of 10 weeks—either working or waiting—the students repeated the battery of tests.

Writing recentlyin JAMA Pediatrics, Hannah Schreier of New York University, Kimberly Schonert-Reichl of the University of British Columbia, and Edith Chen of Northwestern, report that those students assigned to volunteer work finished the semester healthier (lower body mass indexes, better cholesterol levels, fewer inflammatory markers) and happier (less negative, more altruistic and empathetic) than their peers.

Notably, the teenagers’ self-esteem wasn’t affected—suggesting that the effects of volunteerism were so subtle as to be invisible to the students themselves. Yet by helping others, the authors write, the teens were really helping themselves.

Altruism is a slippery thing—am I helping you for your sake, or because it makes me feel generous?—but this is the first study to demonstrate that high school students (not the most selfless of individuals) derive real benefits from mandatory volunteer work, beyond learning that they’re not the center of the universe.

By getting teens off the couch and out of the house, the authors argue, volunteerism has all kinds of impacts on the teenage mind. It forces them to work with (and alongside) individuals from all walks of life, and wrestle with questions of power and privilege. It puts them in contact with other volunteers—the kind of boys you’d like your daughter to bring home for dinner—and normalizes unselfish behavior. Poor emotional well-being—depression, low self esteem—has long been linked to negative "health outcomes" such as cardiovascular disease, the authors write, and because it’s two-way street, improving one side of the equation will necessarily improve the other.

So yes, teenagers are busy, what with calculus and studying for the SAT and college applications and so many episodes of Glee to keep up with. But doing a little volunteer work won’t kill them. In fact, it’s just the opposite.