Men whose index fingers are shorter than their ring fingers were exposed to more testosterone in the womb, and some studies have shown them to have "manlier" traits than men with the opposite pattern. However, a new study shows that manliness could come with a penalty: a higher risk for prostate cancer.
Men whose index fingers are longer than their ring fingers are a third less likely to have prostate cancer than are men whose index fingers are the shorter, according to researchers from the University of Warwick and the Institute of Cancer Research, both in the United Kingdom.
The association is likely rooted in the two genes, called HOXA and HOXD, that control both finger length and sexual development, researchers said.
The study was published Nov. 30 in the British Journal of Cancer.
"The genes involved in how the hand grows seem also to be involved in how the testicles develop," said Peter Hurd, a psychology professor at the University of Alberta in Canada, who has conducted several studies on finger length but was not involved in this study.
Prostate cancer is known to be linked to how sensitive men are to testosterone, Hurd told MyHealthNewsDaily.
When a male fetus develops in the womb, there's a point at which the testicles begin making testosterone. From then on, the amount of testosterone in the developing baby boy influences the relative length of the fingers, as well as the "masculinity" of different parts of the brain, he said.
Previous research indicated that the shorter a man's index finger is compared with his ring finger, the more testosterone he was likely exposed to in the womb. However, there are a number of other factors - such as maternal stress and genetics - that are likely to also play a part, Hurd said.
Looking at the risks
The British researchers identified the relative lengths of these two fingers in 1,500 prostate cancer patients and 3,000 healthy men over a 15-year period. The men were asked to look at pictures of hands and select the one that looked most like their own.
Men whose index fingers were longer than their ring fingers were 33 percent less likely to have prostate cancer than men whose ring fingers were longer, according to the study. In men younger than 60, the risk was reduced further to 87 percent, meaning the effects of low testosterone in utero seem even more pronounced in these younger men.
There was no difference in the risk for prostate cancer between men whose ring fingers are longer than their index fingers - more than half the men in the study - or the 19 percent of men whose ring and index fingers were the same length.
Pointing at past research
But the new finding doesn't mean men who have index fingers shorter than their ring fingers should be overly concerned about prostate cancer, Hurd said.
"Thirty-three percent is still a pretty small effect, so it doesn't make sense for men to look at their own hands and think, 'Oh, I better get screened,'" he said.
Finger length has previously been associated with the development of traits or disease. A 2005 finding that Hurd published in the journal Biological Psychology found that men whose index fingers are shorter than their ring fingers were also more likely to be aggressive than men with the opposite finger-length ratio.
Researchers in Hurd's lab have collected reams of data on finger-length ratios, the length of the arms compared with body height, and facial measurement differences between men and women and among different ethnicities. But not all the findings agree with each other, which highlights that how genes are turned on and off is influenced by more than just prenatal testosterone exposure, he said.
"It's a very noisy relationship, if one exists," he said.