Physical exercise failed to counter the increased heart risk found in among men prone to stress in their teens.
Looking for coronary heart disease (CHD) - which sees a narrowing of the arteries to the heart and can lead to heart attacks - in Swedish registers of the residents born between 1952 and 1956, the study found the following rates per 1,000 person-years associated with each stress-coping profile:
- Low resilience to stress - 2.6 incidences of CHD
- Medium stress resilience - 2.0
- High resilience - 1.6.
Higher physical fitness was also associated with a lower CHD risk, the authors report, but this was "attenuated by low stress resilience." They conclude in the study published in Heart, one of the BMJ journals:
"Low stress resilience in adolescence was associated with increased risk of CHD in middle age and may diminish the benefit of physical fitness."
Overall, between 1987 and 2010, a total of 10,581 diagnoses of heart disease were identified on the Swedish National Patient Register in the group who had also been included on the Swedish Military Conscription Register. Conscription at the age of 18-19 was compulsory for all men born between 1952 and 1956.
The researchers analyzed whether there was any association between heart disease rates and levels of stress resilience after adjusting for established heart risk factors.
There was detailed information on the men's psychological ability to cope as adolescents because the military conscription examination involved semistructured interviews with psychologists for all, measuring their potential to cope with stress during service.
The interviews - which tested readiness for military stress based on "ability to control and channel nervousness, tolerance of stress and disposition to anxiety" - covered various aspects of general everyday life, including:
- Social maturity
- Leisure interests
- Psychological energy
- Emotional stability.
While in Swedish and not fully available for public examination, the results of the military screening - which also examined physical and cognitive function, and diagnoses of disease in adolescence - did enable the researchers to stratify the teenagers by three levels of resilience to stress - low, medium and high.
In addition to finding that low stress resilience was linked to a higher likelihood of CHD, such teenagers were found to be less likely to be physically fit, too.
But even those who were poor at coping but who had good physical fitness did not seem to be protected from heart disease - stress, the researchers say, appears to counter the benefit of physical activity in preventing heart disease.
The authors set out on their analysis knowing that exposure to psychosocial stress had been suggested as a link to a "variety of adverse health outcomes, including coronary heart disease" - but with inconclusive evidence.
Stress may influence metabolic control as well as causing inflammation
"Some studies even suggest a similar magnitude of risk for stress as other major cardiovascular risk factors," they add in their introduction, explaining that this could be due to stress's "influence on the hypothalamic pituitary adrenal (HPA) axis and the sympathetic nervous system, which may alter metabolic and cardiac autonomic control as well as resulting in inflammation."
Stress can also influence lifestyle choices, the authors note. But research to assess CHD risk has given "little attention to the consequences of ability to cope with stress."
They set a secondary hypothesis that "higher-level fitness in adolescence may not be as protective against CHD among those with low stress resilience" - and their results suggest this is true, the authors conclude.
"Our results further suggest that physical fitness varies by stress resilience level and that the protective effect of fitness in adolescence is reduced or eliminated in those with low-stress resilience.
The authors suggest that effective CHD prevention should focus on promoting both physical fitness and tackling stress.
The journal has produced an explanatory video, published at YouTube, to accompany the research paper:
Angry outbursts may raise the risk of heart attack - that was the conclusion of research in the news last week, suggesting that, as well as the chronic effect seen in the present study, psychological and emotional effects can be acute for heart risks.