A low resting heart rate in teenage or early adolescent years has been linked to a greater risk for violent criminality in men in adulthood, European scientists suggest.
Some previous studies have also found a link between a low heart rate to antisocial behavior in children and adolescents, the researchers point out.
The new study has looked at an association between young men's heart rates upon their entry into military service by around the age of 18 and their likelihood of later being convicted of crimes as adults, scientists at the Karolinska Institute in Stockholm and the University of Helsinki report in JAMA Psychiatry.
In the study involving more than 700,000 men born between the years 1958 and 1991 with up to 35 years of follow-up data, those with the lowest resting heart rate as teenagers had a 39 percent greater risk of being convicted of a violent crime later in life than those with the highest pulses, they say.
A slow heartbeat may have psychological effects, the researchers suggest, causing people to find it hard to become excited or aroused, leading them to pursue stimulating experiences — including violent ones — and take more risks.
"Our results confirm that, in addition to being associated with aggressive and antisocial outcomes in childhood and adolescence, low RHR (resting heart rate) increases the risk for violent and nonviolent antisocial behaviors in adulthood," says study leader Antti Latvala of the Karolinska Institute.
A low resting heart rate shouldn't necessarily be considered a problem, some experts are quick to point out.
Lower heart rates are common in very athletic people, whose heart muscles are in better condition and don't need to work as hard to maintain a steady beat, they point out.
Latvala says she agrees that the study findings should be carefully considered.
"It is obvious that low resting heart rate by itself cannot be used to determine future violent or antisocial behavior," she says. "However, it is intriguing that such a simple measure can be used as an indicator of individual differences in psychophysiological processes which make up one small but integral piece of the puzzle."
In addition to the findings on adult violence, men in the study with the lowest resting heart rates during adolescence were more likely to be killed or injured in assaults or to experience serious accidents resulting in injury or death, the researchers found.
"This is a novel finding and it provides support for a more general association between low heart rate and risk-taking behavior," Latvala says.