STATS ARTICLES 2009
BPA and erectile dysfunction
Rebecca Goldin Ph.D, November 17, 2009
Did the numbers on a widely publicized study about Bisphenol A’s effect on the libido add up to a call to Bob Dole? STATS digs into the numbers.
A new study found significant decline in sexual function by Chinese men exposed to high levels of BPA in the workplace. Predictably, this got the environmental activists pretty excited. “BPA Wrecks Sex, Fouls Food -- And Probably Worse” was the headline of a piece by the Environmental Working Group’s Elaine Shannon for the Huffington Post.
The findings, published in the journal Human Reproduction was based on a case-control study in which men exposed to high level of environmental BPA were compared to those with low levels of BPA. While the data are observational, results regarding human exposure to BPA are extremely important, and for that reason the study should be taken seriously.
But before BPA is blamed for American erectile dysfunction, take note: most people in the United States are exposed to amount comparable to the control group of men – that is, the men against which the high-exposure group was compared. The men in the high exposure group had levels of BPA in their urine approximately fifty times as high as those in the control group.
The point of this study was to consider whether men who were exposed to very high BPA levels were more likely than men who were not to suffer from sexual dysfunction.
Currently, the National Toxicology Program, 2008 reported “minimal concern” that men exposed occupationally to BPA will have reproductive effects, and “negligeable concern'” that men exposed at non-occupational role will have reproductive effects. The NTP did not consider, however, sexual function as opposed to fertility, though the NTP brief does note that some laboratory studies of rodents suggest different sexual activity among animals exposed to low doses. Typically, the level of occupational exposure to BPA is still in the “low dose”' category, far below the “high” levels shown to be hazardous to health in laboratory studies.
The results are likely to generate continued interest in the impact that BPA may have on humans, while having no impact on how we evaluate low-level exposure on sexual function or lack thereof.
Now for the details.
The results were by themselves quite significant; they showed a large effect on sexual disfunction. The odds ratio for erectile dysfunction, for example, was 4.5 times as high in men exposed to high levels of BPA, compared to the odds of a low-exposure man experiencing erectile dysfunction. The odds ratio of having trouble ejaculating was 7.1 – in other words, the odds of an occupationally exposed male to have trouble ejaculating is 7.1 times higher than the odds for a man who is not exposed to BPA. These numbers suggest that BPA may well be harming men who are exposed to it at these high levels.
But as mentioned above, the exposure level, which was measured by the presence of BPA metabolites in urine, is far above estimates of the median exposure in the United States.
According to Calafat (et al., 2005), the median BPA level for men and women together is 2.7 micrograms per liter of urine (remember a microgram is a millionth of a gram). The level for men alone is 3.2 micrograms per liter. Unfortunately, the measurement of the Chinese men's urine was in terms of micrograms per gram of creatinine.
Creatinine is a substance found in urine, and its concentration varies in part on how much water someone drinks before providing a urine sample. The mean concentration of BPA in the urine of Chinese men who were not occupationally exposed to BPA was 1.2 micrograms per gram of creatinine. In contrast, the men with occupational exposure had a mean of 57.9 micrograms per gram of creatinine.
In order to compare the BPA levels of the Chinese men with those who provided the median levels to the NTP report, we need to know the converstion of grams of creatinine per liter of urine. This varies individually, but according to an article published in Environmental Health Perspectives, the average for men is 148 milligrams per deciliter. This does not necessarily apply to Chinese men, of course, but we use them for a “back of the envelope” calculation to find the median level of BPA per gram of creatinine in the NHANES III participants.
Recall that a deciliter is one tenth of a liter. Therefore: 148 milligrams of creatinine per decliter = 1,480 milligrams per liter =1.48 grams of creatinine per liter.
Therefore, a BPA level of 3.2 micrograms per liter is approximately 3.2/1.48 micrograms BPA per gram of creatinine, or about 2 micrograms of BPA per gram of creatinine. This is comparable to the 1.2 micrograms found in the non-occupationally exposed men.
This means that the median BPA level for occupationally exposed Chinese man (57.9 micrograms per gram of creatinine) is at least 25 times the exposure of the median American exposure. The Chinese exposed group also contained men with much, much higher levels of exposure even than this. The 75th percentile of Chinese exposure is 467 micrograms per gram of creatinine. This is more than 200 times the median American exposure.
Even the 95th percentile of American men came in at 16 micrograms of BPA per liter of urine, or approximately 11 micrograms BPA per gram of creatinine (we obtained 11 by dividing 16micrograms/liter by 1.48 grams creatinine per liter).
This suggests that while the median Chinese (half had more, half had less) BPA exposure was 58 micrograms BPA per gram creatinine, those that had more exposure had MUCH more exposure.
There are a few concerns with the quality of the research that may have exaggerated the results, even among occupationally exposed men. We noted three confounders that may impact the results. First, the authors noted that the workers are generally less educated. They did control for this in the study. However, if less educated workers are more likely to work in more physically demanding jobs, which in turn could then have an impact on sexual interest/satisfaction/ability, and at the same time these more demanding jobs are with factories using BPA, we wouldn't know.
Another important factor is other environmental exposure to toxins: the authors have adjusted for this, but they did not list how they determined which other chemicals/toxins people more likely to be exposed to BPA would also be more likely to experience.
Finally, while the authors claim that the subjects did not know their BPA status, it is possible that the men suspected that their factories were exposing them to possibly toxic chemicals and were more inclined to report sexual problems. The study did not include any questions in their survey as to their possible knowledge or suspicions.
Without a doubt, this study will generate interest in the question of the impact of BPA in occupationally-exposed men. However, no conclusions can be drawn regarding male sexual function regarding non-occupationally exposed men, except that they have more sexual satisfaction than their occupationally exposed brethren.