Men with certain types of baldness may be at higher risk for coronary heart disease, a research review suggests.

Researchers at the University of Tokyo looked at data from almost 37,000 men in the U.S. and Europe over a 14-year period. They found that where hair was lost mattered.

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Younger men balding at the top of their heads might be encouraged to improve their diet and exercise habits. (iStock)

"Vertex [crown] baldness, but not frontal baldness [receding hairline], is associated with an increased risk of coronary heart disease," Dr. Kazuo Hara and co-authors concluded in their review published in the journal BMJ Open.

"Cardiovascular risk factors should be reviewed carefully in men with vertex baldness, especially younger men, and they probably should be encouraged to improve their cardiovascular risk profile."

The usefulness of screening healthy people for heart disease is unknown and no direct link was established, they cautioned, noting some of the studies had inconsistent results.

As for why there might be an association, it's unclear.

Cardiologist Dennis Ko of Sunnybrook Health Sciences Centre in Toronto suspects factors that affect both the heart and hair.

"There are changes in sex hormones like androgen and testosterone in patients with baldness," Ko said. "Some of those may also be affecting the vessels of the heart."

Previous studies have also raised the possibility that insulin resistance, diabetes, chronic inflammation or sensitivity to testosterone, all of which may lead to cardiovascular disease, could be playing a role in male baldness.

The balding association was far weaker than the link between heart disease and well-known risk factors such as smoking, obesity and high blood pressure.

With files from CBC's Kim Brunhuber and the Australian Broadcasting Corporation