Teenagers who suffer with major depression or bipolar disorder should have their heart health closely monitored, as they are at an increased risk of developing early heart disease, experts have warned.

In a new scientific statement, the American Heart Association insisted that these mental health conditions should be seen as independent risk factors for heart disease among adolescents. The statement is based on a comprehensive analysis of recent scientific studies on this topic.

"Youth with mood disorders are not yet widely recognised as a group at increased risk for excessive and early heart disease. We hope this statement will spur action from patients, families and healthcare providers to reduce the risk of cardiovascular disease among these youth," commented the statement's lead author, Dr Benjamin Goldstein, of the University of Toronto in Canada.

Symptoms of major depression can include persistent feelings of sadness and a loss of interest in activities that were previously enjoyed. Symptoms of bipolar disorder can include severe mood swings that range from depression to mania. During a manic phase, people may experience increased energy and elation, but also increased irritability.

Previous studies have already found that adults with these conditions are much more likely to have heart disease, however after carefully analysing the latest published research, the experts found that teenagers with these conditions are much more likely to have several risks factors for heart disease compared to their peers.

These risk factors include high cholesterol, high blood pressure, type 2 diabetes and atherosclerosis (hardening of the arteries).

The experts acknowledged that teenagers with mental health conditions were more likely to partake in unhealthy behaviours, such as smoking, drug abuse and a lack of exercise. However, these factors alone were not able to explain the increased heart risk found in these young people.

Based on their findings, the experts stated that major depression and bipolar disorder should be included as moderate risk factors for heart disease in teenagers.

"Mood disorders are often lifelong conditions, and managing cardiovascular risk early and assertively is tremendously important if we are to be successful in ensuring that the next generation of youth has better cardiovascular outcomes. These disorders indicate an increased risk of heart disease that requires increased vigilance and action at the earliest possible stage," Dr Goldstein said.

The scientific statement is published in the medical journal, Circulation.

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