Researchers have long observed that men who lose their hair tend to develop heart disease at an early age.
But a new analysis by Japanese researchers has found that not all forms of baldness carry the same degree of cardiovascular risk.
They combed through the medical literature, searching for top-notch studies on the topic. After reviewing 850 papers, they settled on six that met their high-quality criteria. The studies, involving almost 40,000 men, were published between 1993 and 2008.
The meta-analysis of the combined data showed that the greatest heart risk was for men whose hair was thinning on top of the head, or crown, known as vertex baldness.
And the more hair they lost, the greater their risk, according to the findings published this week in the online journal BMJ Open.
The study contained some good news for men with receding hairlines. This form of hair loss is not a harbinger of heart troubles.
Still, the researchers acknowledged their assessment is based on a fairly small number of studies. To further complicate matters, not all the studies measured hair loss in the same way. To get around this methodological problem, the researchers created their own grading system of baldness: none, frontal, crown-top and combined.
"Men with both frontal and crown-top baldness were 69 per cent more likely to have coronary artery disease than those with a full head of hair, while those with just crown-top baldness were 52 per cent more likely to do so. Those with just frontal baldness were 22 per cent more likely to do so," said a statement released with study.
So why is hair loss linked to heart disease?
"The reason for the association between baldness and cardiovascular diseases is unclear," one of the researchers, Dr. Tomohide Yamada of the University of Tokyo, said in an e-mail.
But he speculated that both conditions might arise from some of the same underlying biological factors.
For instance, insulin-resistance — leading to elevated blood-sugar levels — can damage blood vessels and contributed to the onset of heart disease. In a similar fashion, insulin resistance can "cause vasoconstriction and impair the supply of nutrients to the hair follicles of the scalp" which could trigger hair loss.
Hormones might also play a duel role. Yamada noted that testosterone is converted into a compound that leads to the "miniaturization of hair follicles." There is also some evidence to suggest a testosterone byproduct contributes to the buildup of fats inside blood vessels, a hallmark of atherosclerosis.
The study's findings could help doctors identify high-risk patients who may need extra medical attention so they don't succumb to heart disease while they are still in their prime.
"Younger men with vertex baldness probably should be encouraged to improve their cardiovascular risk profile," said Yamada. That could mean making sure they get regular exercise and sticking to a heart-healthy, low-fat diet.