Teenagers who are anxious or depressed may have an increased risk of going on to suffer a heart attack later in life, a new study has suggested.

Swedish researchers set out to investigate whether conditions like depression in adolescence are linked with an increased risk of cardiovascular disease in adulthood.

They looked at over 238,000 men born in the 1950s who had undergone extensive medical and psychiatric examinations in late adolescence - 18 or 19 years of age - as part of their assessment for compulsory military service. The men were then followed up for many years, until they reached an average age of 58.

Over 34,500 were diagnosed with a non-psychotic mental disorder, such as anxiety or depression, when they were aged 18 or 19. Their cardiovascular health was then assessed using hospital records.

The study found than those with a mental health problem in adolescence, such as depression or anxiety, had a 20% increased risk of suffering a heart attack by middle age, compared to those without a mental health problem.

The results stood even after other factors were taken into account, such as blood pressure, body mass index and general health.

The link was partly explained by poorer stress resilience and lower physical fitness in teenagers with a mental illness.

"We already knew that men who were physically fit in adolescence seem less likely to maintain fitness in later years if they have low stress resilience. Our previous research has also shown that low stress resilience is also coupled with a greater tendency towards addictive behaviour, signalled by higher risks of smoking, alcohol consumption and other drug use," explained the study's author, Dr Cecilia Bergh, of Örebro University in Sweden.

She called on parents to "be vigilant and look for signs of stress, depression or anxiety that is beyond the normal teenage angst".

"Seek help if there seems to be a persistent problem. If a healthy lifestyle is encouraged as early as possible in childhood and adolescence, it is more likely to persist into adulthood and improve long-term health.

"Better fitness in adolescence is likely to help protect against later heart disease and may also alleviate some of the negative consequences of stress. This is relevant to all adolescents, but those with poorer wellbeing could benefit from additional support to encourage exercise and to develop strategies to deal with stress," Dr Bergh added.

Details of these findings were released at the European Society of Cardiology Congress 2020, which is being held digitally this year.