“Men who go bald by the age of 40 are more likely to get prostate cancer”, reports the Daily Mail today.
But before balding men get depressed about the ‘double- whammy’ of losing their hair and having an increased risk of dying from cancer – this study did not look at mortality rates. Many cases of prostate cancer are non-aggressive (slow growing) – leading to an old medical saying – ‘Most men die with prostate cancer, not from it’.
Nonetheless, a diagnosis of prostate cancer can be serious and a significant number of men die from the disease each year.
This headline is based on research showing the relationship between male pattern baldness (the most common type of baldness) and being diagnosed with prostate cancer varies according to age.
Many researchers have suggested that higher levels of testosterone may trigger the development of cancerous cells, while also inhibiting hair growth – which provides one plausible explanation for the link.
Up to the age of 76 years, men showing signs of baldness at 40 were generally at a higher risk of being diagnosed with prostate cancer. This was not the case at older ages and in fact, the relationship reversed. The risk of developing prostate cancer at 76 years old was approximately 15%, regardless of any hair loss at 40.
Despite the newspaper saying testosterone may be the cause of the relationship, the study didn’t measure or assess testosterone levels in any way. It would be useful if further research measured testosterone levels to see whether it actually is part of the cause of the pattern observed.
Where did the story come from?
The study was carried out by researchers from the University of Melbourne and the Cancer Epidemiology Centre in Victoria, Australia. It was funded by National Health and Medical Research Council grants, the Cancer Council Victoria, and VicHealth.
The study was published in the peer-reviewed science journal: Cancer Epidemiology, Biomarkers and Prevention.
The Daily Mail’s coverage of the story was generally accurate, but there was no discussion of the limitations of the research.
What kind of research was this?
This was a cohort study investigating a potential link between signs of male male pattern baldness at either the age of 20 or 40, and the risk of developing prostate cancer years later.
The researchers stated that both prostate cancer and male pattern baldness are strongly related to age and that this may be due to differences in hormone levels. However, this link is not clear-cut.
Previous research, involving case-control studies, has found contradictory results. Some studies found a link between male pattern baldness and an increased risk of prostate cancers, but other studies found precisely the opposite.
For this reason, the researchers wanted to investigate this issue further in this study.
A cohort study typically follows healthy people for decades or more and records the diseases they eventually develop and in some cases, die from. Researchers then look back at information recorded in the previous years for links between the disease and the characteristics or behaviour of the different people in the cohort.
What did the research involve?
At the start of the study, 9,448 men aged 20 or 40 years old were asked to assess their hair pattern relative to eight picture examples displayed on cards.
This was to assess the degree to which they had male pattern baldness, also known as androgenetic alopecia.
The typical pattern of male baldness begins at the front hairline. The hairline gradually moves backwards (recedes) and forms an "M" shape. Eventually the hair becomes finer, shorter, and thinner, creating a U-shaped pattern of hair around the sides of the head. The eight different cards helped sort the men into different severities of pattern baldness.
Cases of prostate cancer in the men of the cohort were notified to the Victorian Cancer Registry between the time they were enrolled in the study (1990-1994) and when they were followed up over a decade later (2003-2009).
After a diagnosis of prostate cancer had been made, or the trial came to an end, the researchers looked to see if diagnosis of prostate cancer in later life was related to their baldness pattern at age 20 or 40.
The researchers tried a variety of statistical techniques to tease out the overall and age related differences in the relationship.
These were broadly appropriate, although it was unclear how much of the analysis was pre-planned and how much was carried out in an attempt to ‘fish’ for a significant result.
What were the basic results?
The study analysed 9,448 men, who were followed up for an average of 11 years and 4 months; during this time there were 476 cases of prostate cancer. This equates to approximately 5% of the men in the study, or about 1 in 20.
Male pattern baldness was not very common in the men aged 20, just 7% reporting balding, and was higher at age 40, with 37% of men reporting some level of balding.
Overall, analysis of all the men over the 11 years found no evidence to suggest that male pattern baldness at 40 years was associated with risk of prostate cancer.
However, analysing the risk of prostate cancer by age found a more complex two-way relationship.
Essentially, at younger ages, there was an increase in the risk of prostate cancer in those showing signs of pattern baldness at 40 (compared to those that didn’t). However, this trend was reversed by the time the men reached 80 – if men with a history of male pattern baldness lived to this age, they were less likely to develop prostate cancer than men without a history of baldness.
The point where the risks were identical was around 76 years old. At this point, both groups (those showing signs of pattern baldness at 40 and those not) had a similar chance of being diagnosed with prostate cancer, which was approximately 15%.
Further analysis indicated those showing signs of pattern baldness at 40 years were diagnosed with prostate cancer an average of 2.77 years younger (95% confidence interval [CI] 1.4 to 4.14 years) than men without any signs of baldness at 40.
As so few men aged 20 showed signs of pattern baldness, there was not enough data to reliably estimate the risk of prostate cancer in this group.
How did the researchers interpret the results?
The researchers concluded that the relationship between male pattern baldness and prostate cancer incidence was heavily influenced by age and the relationship was different at different age brackets.
Overall, they indicated that men with male pattern baldness at 40 had a higher cumulative risk of prostate cancer up to the age of 76 years, compared to those with no signs of baldness, but after this age, the risk was similar in both groups.
This well designed trial indicates that the relationship between male pattern baldness and incidence of prostate cancer varies depending on age. Up to the age of 76 years, those showing signs of baldness at 40 are generally at higher risk, but this is not the case at older ages. The risk of having prostate cancer in men over 76 years old was around 15%, regardless of hair loss at 40.
This trial had many strengths, including its design and large sample size. However, the following limitations should be considered when interpreting the results of the study:
- The study did not test any biological mechanism explaining how male pattern baldness at 40 years might influence prostate cancer. However, studies in the past that have found similar relationships suggest testosterone might be important. This hormone is known to promote cancer tumour growth in some circumstances and is linked to male baldness. Despite being a plausible explanation, there are others and as of yet there is no concrete explanation for these results.
- The study only had a small number of aggressive cancers, most were non-aggressive. It is a real possibility that those with more aggressive cancers were less likely to remain in the study until the end (were too ill or died), and so were not in the analysis, than those with more mild cancers. Hence, the results are mainly applicable to non-aggressive prostate cancer.
- It is important to bear in mind that men aged 76 years had exactly the same risk of being diagnosed with prostate cancer (around 15%) regardless of their hair pattern at 40. It was only at younger ages when the risk was higher in bald men, suggesting they were diagnosed younger. Crucially, this research only looked at diagnosis of prostate cancer, rather than deaths due to it.
- This current research does not tell us whether survival from prostate cancer is linked to male pattern baldness in earlier life in any way. This would be an interesting outcome to investigate.
- The self-assessment of baldness may have introduced some error into the study (recall bias), but given the size of the study, this is unlikely to have affected the overall results.
This is an interesting study that raises some important questions about the shared biology of male pattern baldness and prostate cancer, which could potentially lead to new treatments for both in the future. Indeed, there is a medication called finasteride, which is currently used to treat both prostate enlargement and male pattern baldness.