Male pattern baldness is linked to an increased risk of coronary heart disease, but only if it's on the top/crown of the head, rather than at the front, finds an analysis of published evidence in the online journal BMJ Open.
A receding hairline is not linked to an increased risk, the analysis indicates.
The researchers trawled the Medline and the Cochrane Library databases for research published on male pattern baldness and coronary heart disease, and came up with 850 possible studies, published between 1950 and 2012.
But only six satisfied all the eligibility criteria and so were included in the analysis. All had been published between 1993 and 2008, and involved just under 40,000 men.
Three of the studies were cohort studies - meaning that the health of balding men was tracked for at least 11 years.
Analysis of the findings from these showed that men who had lost most of their hair were a third more likely (32%) to develop coronary artery disease than their peers who retained a full head of hair.
When the analysis was confined to men under the age of 55-60, a similar pattern emerged. Bald or extensively balding men were 44% more likely to develop coronary artery disease.
Analysis of the other three studies, which compared the heart health of those who were bald / balding with those who were not, painted a similar picture.
It showed that balding men were 70% more likely to have heart disease, and those in younger age groups were 84% more likely to do so.
Three studies assessed the degree of baldness using a validated scale (Hamilton scale). Analysis of these results indicated that the risk of coronary artery disease depended on baldness severity, but only if this was on the top/crown of the head, known as the vertex.
Extensive vertex baldness boosted the risk by 48%, moderate vertex baldness by 36%, and mild vertex baldness by 18%. By contrast, a receding hairline made very little difference to risk, the analysis showed.
To compensate for differences in the methods of assessing baldness in the studies included in the analysis, the authors looked at four differing grades of baldness: none; frontal; crown-top; combined.
Once again, this indicated that the severity of baldness affected the risk of coronary heart disease.
Men with both frontal and crown-top baldness were 69% more likely to have coronary artery disease than those with a full head of hair, while those with just crown-top baldness were 52% more likely to do so. Those with just frontal baldness were 22% more likely to do so.
Explanations for the reasons behind the association vary, but include the possibility that baldness may indicate insulin resistance, a precursor to diabetes; a state of chronic inflammation; or increased sensitivity to testosterone, all of which are involved directly or indirectly in promoting cardiovascular disease, say the authors.
But they conclude: "[Our] findings suggest that vertex baldness is more closely associated with systemic atherosclerosis than with frontal baldness. Thus, cardiovascular risk factors should be reviewed carefully in men with vertex baldness, especially younger men" who should "probably be encouraged to improve their cardiovascular risk profile."
[Male pattern baldness and its association with coronary heart disease: a meta-analysis doi 10.1136/bmjopen-2012-002537]