Bald men are at greater risk of developing heart problems than those who retain a full head of hair – but only those with hair loss on top of their heads, and not at the front, are affected, new research suggests.

While baldness is associated with an increased risk of coronary heart disease (CHD), men who have a receding hairline are not at heightened risk of the condition, according to a study in the journal BMJ Open.

Researchers in Japan who examined six previous studies from Europe and America of the link between baldness and CHD, comprising 36,990 men, found that five of the studies confirmed an association.

Men who have lost most of their hair are 32% more likely to go on to develop heart trouble compared with full-headed peers, according to three studies, which tracked men's health for at least 11 years. But men aged less than 55-60 were 44% more likely to suffer coronary artery disease, the researchers say. The three other studies put the increased risk even higher: at 70% for balding men overall and 84% for younger men.

The authors said that in their meta-analysis "vertex baldness was significantly associated with an increased risk of CHD among younger men as well as among all participants, and the association was dependent on the severity of baldness. Vertex baldness is more closely associated with systemic atherosclerosis [hardening of the arteries] than with frontal baldness."

But Doireann Maddock, senior cardiac nurse at the British Heart Foundation, said: "Although these findings are interesting, men who've lost their hair should not be alarmed by this analysis." Further research was needed to prove any link between baldness and increased risk of CHD and, pending that, "it's more important to pay attention to your waistline than your hairline," she added.

Experts in statistics and risk also urged caution. David Spiegelhalter, professor of the public understanding of risk at Cambridge University, said: "I am sceptical about the claim that different types of baldness have varying associations with heart disease." The research had not made a causal link between baldness and heart disease and it may simply be that a common factor was involved in both, he said.

The research had found an increase in a man's relative risk of CHD, said Patrick Wolfe, a professor of statistics at University College London. "So, if we consider the case of two male, non-smoking marathon runners in top physical condition, one of whom is bald and the other not, then their absolute risks for heart disease are likely to be quite small – despite the fact that their relative risks may be different – both because of baldness and because of other factors, including family history."