Losing hair at the crown of the head may signal an increased risk of heart disease in men.
The strength of the association depends on the degree of baldness, researchers at the University of Tokyo's department of diabetes and metabolic diseases found by reviewing past studies. No link to heart disease was found for men with a receding hairline, said the scientists, who reviewed six studies with a total of almost 37,000 participants. Their findings were published in the BMJ Open medical journal.
Hair loss has been associated with the risk of developing prostate cancer in previous research. Baldness may be a sign of increased resistance to insulin, a precursor to diabetes; a state of chronic inflammation; or increased sensitivity to the male sex hormone testosterone, and those conditions may lead to the development of cardiovascular disease, the researchers said.
"The present meta-analysis provided useful evidence regarding the potential influence of baldness on coronary heart disease," the authors said in the published paper. "Patients and physicians should consider the possibility that baldness is associated with an increased risk."
Three of six studies analyzed tracked the participants' health for at least 11 years. They suggested that men who had lost most of their hair were a third more likely to develop heart disease than peers who retained a full head of hair.
The other three studies showed that balding men were 70 percent more likely to have heart disease, the researchers found. The more extensive the baldness, the higher the risk, they said. The scientists got no specific grant to fund the study, they said.
"It is important to remember that the study reports an increase in relative risk," said Patrick Wolfe, a professor of statistics at University College London.
Comparing two nonsmoking males in good physical condition, one of whom is bald and the other not, their absolute risks for heart disease are likely to be very small, even if their relative risks may be different, Wolfe said.
"In the meantime, it's a case of focusing on the things that we can control -- our diet, exercise regimes and other risks factors -- to lower our overall risk for heart disease," he said.