Despite the fact that benign prostatic hyperplasia (BPH) – or simply, prostate enlargement impacts so many people and carries with it a huge price tag – estimated at tens of billions of dollars per year in medical expenses and lost wages, among other costs – the factors that contribute to BPH have yet to be positively identified.
However, a new study conducted by University of California Santa Barbara (USCB) anthropologists suggests that the hormone testosterone – specifically, an unnatural overabundance thereof – may be a prime culprit. Building on previous research they conducted with the Tsimane, an isolated indigenous population in central Bolivia, Dr Benjamin Trumble and Dr Michael Gurven examined the prevalence of BPH among a group of approximately 350 adult males. Within that group, advanced cases of prostate enlargement were practically non-existent. As a correlating factor, the Tsimane also have relatively low levels of testosterone that remain constant over their lives.
"Abdominal ultrasounds show they have significantly smaller prostates – and age-adjusted 62% smaller prostate size – as compared to men in the US," said Trumble, a post-doctoral scholar at UCSB and the paper's lead author. "BHP is not inevitable for Tsimane men." "We also know testosterone and androgens are involved because of studies showing that eunuchs and people who don’t have testes have very low rates of BPH," Trumble added.
"Some of the best pharmacological BPH and prostate cancer treatments involve reducing androgen levels. We also know from our own previous research that Tsimane have relatively low levels of testosterone – about 30% lower than age-matched US males – and they have very low rates of obesity and hypertension and heart disease and all the other diseases of acculturation, including metabolic disease."
Despite having low testosterone overall, Tsimane men with higher testosterone levels (but still significantly lower than those of men in industrial populations) have larger prostates. According to the researchers, this has important implications for the millions of men who use testosterone supplements to counteract low testosterone. They may be putting themselves at risk for prostate enlargement.
"Basically, these guys taking testosterone replacement therapies are entering themselves into an uncontrolled experiment," said Trumble. "And this happened to women with oestrogen replacement therapy from the 1980s to the early 2000s. And then the Women's Health Initiative study came out and showed that all these women were putting themselves at risk for breast and other cancers."
Although this particular study did not test for prostate cancer, other studies have shown that population differences in testosterone impact prostate cancer risk as well, according to Trumble. "Populations with higher testosterone exposure appear to have higher rates of prostate cancer," he said. "And similar to those for BPH, many of the pharmacological treatments for prostate cancer block androgens."
The researchers' findings raise questions about the health benefits – and risks – that come from our attempts to thwart Mother Nature. "In American men, testosterone levels decrease with age," said Gurven, a professor of anthropology and senior author of the paper. Gurven also is co-director of the Tsimane Health and Life History Project, a joint effort of the University of New Mexico and UCSB. "It's easy to look at that pattern and think, 'Well, if I want to reverse the aging process, I only need to return to the high levels of testosterone of my vigorous youth.'"
"But there's probably a reason your body is producing less testosterone than it used to, and if you try to trick it and flood it with testosterone supplements, you may see some beneficial effects – people report feeling more energised, having a stronger libido – but at what cost?" he continued. "Perhaps even if you knew the costs, you'd still make the decision to use testosterone replacement therapy and discount the risks relative to the potential gains, but understanding those risks is vital in order to make an informed decision." The bottom line: More long-term studies of testosterone replacement therapy in men are necessary to ensure its safety and efficacy.
"Something else we found is that even the men who did have anatomical BPH beyond a certain cut-off, the size that would require treatment in the US, those were exceedingly rare," said Trumble. "About 50%of men in their 70s in the US have prostates larger than 40 cubic centimeters, which is the level where they start looking at major medical interventions. For the Tsimane, less than 1% of all men in the study had prostates larger than 40 cubic centimeters. "Not only were they smaller, but those that were relatively larger were still much smaller than what you’d see in the US," Trumble added, "and smaller than what would require treatment."
In addition to measuring prostate size, the researchers looked at the levels of glycated hemoglobin in the subjects’ blood. Glycated haemoglobin – HbA1c – is a measure of long-term glucose exposure that in turn indicates the risk of diabetes. "Despite having sub-clinical levels of HbA1c, men with higher HbA1c had larger prostates," said Trumble. "Not one of the men in this study had HbA1c indicative of diabetes. These were all men with relatively low glucose levels. Among men with low testosterone and low diabetes risk, those with relatively higher testosterone or HbA1c were at higher risk of prostate enlargement," he said.
[link url="http://www.news.ucsb.edu/2015/015419/when-it-comes-testosterone-more-isnt-always-better"]University of California Santa Barbara[/link]
[link url="http://biomedgerontology.oxfordjournals.org/content/early/2015/04/28/gerona.glv051.abstract?sid=9e32f218-1b29-49c6-bc58-be27ef3af81b"]Journal of Gerontology: Medical Sciences abstract[/link]