Sperm quality seems to be decreasing, and researchers think they have found the reason why. Bisphenol A (BPA) and other chemicals in the environment may be reducing fertility in men, the researchers say.
BPA is a chemical commonly found in plastic containers and thermal cash register receipts, among other items. The chemical mimics estrogen, a hormone that can interfere with testosterone in men. BPA belongs to a class of chemicals called endocrine disruptors because they can interfere with how hormones function within the human body, including birth control hormones that can end up in the water supply from sewage treatment plants.
There has been increasing evidence that BPA can cause health problems, and increasing calls to find alternatives to the chemical in manufactured goods. The chemical has already been banned in baby bottles in the U.S. but is still present in a wide variety of other everyday products.
The latest study from geneticist Patricia Hunt and her team at Washington State University, published in PLoS Genetics, looked at how exposure to chemicals such as BPA early in life affected sperm production later on. The researchers exposed newborn mice to either BPA or the type of synthetic estrogen used in birth control pills. The low-dose exposure was comparable to what humans might face in their everyday lives.
The scientists looked at the effect these early exposures to BPA and synthetic estrogen had on those mice, but also transplanted their stem cells into unexposed mice. The team confirmed what other researchers had already found, that BPA exposure can affect reproductive properties like the size of the mice testes, sperm development, and prostate growth. However, they also found that the changes were linked to the stem cells, so even a brief exposure to these chemicals early in life can affect reproduction for years to come.
The BPA exposure seemed to cause the sperm cells to have problems during meiosis. This caused more sperm to die off, leading to a lower sperm count.
Doctors for the past few decades had noted a decline in sperm counts around the world, with about 40 percent of young men in Denmark experiencing decreased fertility. This could not only affect individuals hoping to start a family, but the population as a whole as men become less able to reproduce. Sperm quality may also be affected by BPA and similar chemicals. As well, the chemicals could cause genetic changes, so the low fertility could be passed down from one generation to the next. This could have an increasing effect on each generation as they inherit changes related to past BPA exposure and are themselves exposed to the hormone-disrupting chemicals.
Low sperm count is not the only problem men may be facing from BPA exposure. Doctors have also noted higher incidences over time of abnormalities in male genitalia, such as undescended testes, as well as increasing rates of testicular cancer. Researchers note these other reproductive problems could also be caused by early BPA exposure.
BPAs are not the only chemicals that may be putting health at risk. In another study, researchers found that about a third of the chemicals they studied affected sperm swimming behavior. They had looked at just under a hundred different chemicals found in common household items such as plastic toys, soap, and toothpaste.