Researchers studying the links between childhood depression, divorce, and smoking highlight the importance of good mental health in kids and teens.

New research on teen depression reveals that those with depression are 13 times more likely to pick up smoking, and that the children of divorced parents are about 50 percent more likely to take up the habit.

According to the Centers for Disease Control, cigarette use among youth has declined over the past decade, but 19.5 percent of high school students report smoking one or more cigarettes in the past month.

The two newest studies examined the impact of divorce and childhood depression, and found that these two factors drastically increase a child’s likelihood of becoming a regular smoker.

Researchers at the University of Toronto analyzed data from 19,000 Americans and found that men and women whose parents divorced before they turned 18 were 48 percent and 39 percent, respectively, more likely to smoke. Researchers also took other factors, such as anxiety and depression, into account.

Calling the link “disturbing,” lead author Esme Fuller-Thomson, the Sandra Rotman Chair at the University of Toronto’s Factor-Inwentash Faculty of Social Work, published her findings in the latest issue of the journal Public Health.

Researchers were unable to determine precisely why the children of divorced parents tend to pick up smoking, but co-author Joanne Filippelli, a University of Toronto doctoral student, said that children may light up to cope with the stress of the divorce.

“Some research suggests this calming effect may be particularly attractive to those who have suffered early adversities,” she said.

Researchers at the Washington University School of Medicine in St. Louis and the University of Pittsburgh explored the link between childhood depression and an increased risk of cardiac problems, including a greater risk of dying from a heart attack.

The researchers studied 201 children with clinical depression, 195 of their siblings, and 161 other children without depression. They examined the children at about age nine and again around age 16, recording their rates of obesity, physical activity, and cigarette smoking.

Besides the fact that one-third of the depressed children were daily smokers by age 19—compared with only 2.5 percent of their non-depressed peers—researchers found that nearly a quarter of the depressed teens were obese and that they were the least active of all three groups overall.

Researchers can’t say that depression directly causes an increased risk of heart problems, but the behaviors associated with depression, including inactivity and cigarette smoking, can increase cardiac risk.

It’s been widely documented that these factors all contribute to cardiac problems, including heart disease, heart attack, and stroke.

“Depression seems to come first,” first author Robert M. Carney, a professor of psychiatry at Washington University, said in a press release. “It’s playing an important, if not a causal, role. There may be some related genetic influences that give rise to both depression and to heart disease, or at least to these types of cardiac risk behaviors, but more study will be required before we can draw any firm conclusions about that.”

The researchers reported their findings Friday at the annual meeting of the American Psychosomatic Society.

These studies highlight the importance of properly (and promptly) treating mental health issues in children.

Previous research has shown that childhood stress, depression, and obesity can lead to adverse health effects beyond smoking. This includes an increased risk of alcohol use and suicide.

Because cigarette smoking is one of the leading causes of chronic illness and premature death, the Toronto researchers said, smoking prevention programs targeted at children whose parents are divorcing may be helpful.

Also, advocating a healthy, active lifestyle has been shown to help children cope with stress more effectively so that they don’t pick up bad habits.