Laudan Aron is a senior research associate in the Urban Institute’s Labor, Human Services and Population center. In this post, borrowed from the Urban Institute’s Metro Trends blog, she looks at the health of teenagers as an indicator of a community’s overall culture of health.

Last week, I shared a starter list of principles that can help guide health-promoting community investments. That list was inspired by a large and growing body of research on the social determinants of health: conditions within our families, neighborhoods, and communities that shape our health and survival. That same body of research points to an important period in life that is unique in its ability to shed light on a community’s culture of health: adolescence.

The health of teenagers is a powerful signal of the health of an entire community, and also a leading indicator of the future health of that community. Just as infant mortality has been a touchstone indicator of overall economic development and progress in less developed countries, in more advanced countries and societies, adolescent health is that measure. These are the years when the social determinants of health really kick into action.

Adolescence is when young people start to step out from the protection and oversight of their immediate families. The broader influences of peers, coaches, mentors, faith-based leaders, and social media start to accelerate—for good or bad.  As Russell Viner and his colleagues argue, communities “present young people with structures of opportunity” that “are crucial to the health of the whole population and the economic development of nations.” Population-level measures of adolescent health allow us to identify how well communities are supporting lifelong healthy human development, providing healthy social and physical environments from early in life, and preserving health and preventing injury and illness in the first place.

Preadolescence and adolescence are sensitive periods developmentally. Teens are highly susceptible to socialization processes and behaviors that can promote or derail their health, including sensation seeking and experimentation with alcohol, smoking, other drugs, and sex. The foundations of lifelong health behaviors are also often set at this stage of life: habits relating to diet, exercise, sleep, and stress management.

Many adult chronic illnesses (the same ones that are consuming 75 percent of our health care dollars) can be traced back to decisions and behaviors from this stage of life. This is also the time when young people’s capacities for abstract thinking and future planning start to form, and qualities like self-image, self-control, and motivation take shape.

Most serious and persistent mental illnesses—from depression to schizophrenia—first appear in adolescence. This is also the peak period when young people disconnect from mainstream developmental pathways, possibly due to unidentified or unattended learning disabilities; mismanaged behavioral disorders; and trauma, abuse, or neglect at home. Decisions to drop out of school, join a gang, run away from home, drive while drunk, or have unprotected sex can have lifelong consequences—including health consequences—that span generations.

So while our investments and interventions should start at the very earliest stages of life, we should not lose sight of our teens. Their health and well-being have a lot to tell us about how well we are doing as a society and what the future holds.