TUESDAY, Jan. 7, 2014 (HealthDay News) -- A study with mice suggests that exposure in the womb to the plastics chemical bisphenol A (BPA) could put males at greater risk for prostate cancer later in life.

The findings are early, however, and can't prove a causal link between BPA exposure and the cancer.

According to background information from the study's authors, BPA is commonly used in everyday products such as water bottles and soup cans, and boosts stem cells' sensitivity to estrogen. Estrogen is found naturally in both men and women.

Over time, heightened sensitivity to the hormone might raise men's vulnerability to illnesses such as prostate cancer, the researchers said.

"Our research [in mice] provides the first direct evidence that exposure to BPA during development, at the levels we see in our day-to-day lives, increases the risk for prostate cancer in human prostate tissue," study lead author Gail Prins, professor of physiology and director of the andrology laboratory at the University of Illinois at Chicago, said in a university news release.

"The findings of adverse effects of BPA in human tissue are highly relevant and should encourage agencies like the U.S. Food and Drug Administration to re-evaluate their policies in the near future," Prins said.

In conducting the study, which was published online Jan. 7 in the journal Endocrinology, the researchers took human prostate stem cells from young men who died and implanted them into mice. The mice were then fed BPA two weeks after implantation to copy the effects of BPA exposure that would be similar to that of a baby in the womb.

The mice were given doses of BPA similar to levels detected in pregnant American women, the researchers said. "The amount of BPA we fed the mice was equivalent to levels ingested by the average person," Prins said. "We didn't feed them exorbitantly high doses."

One month later, the mice were given estrogen to mimic the levels of the hormone, which rise naturally among men as they age. After two to four months, tissue samples were taken from the mice and screened for prostate cancer.

The study found that one-third of the tissue samples taken from mice that had been fed BPA had either pre-cancerous lesions or prostate cancer. The same was true for only 12 percent of the mice in the control group that were not fed BPA.

Meanwhile, 45 percent of the prostate stem cells exposed to BPA both before and after being implanted in the mice had pre-cancerous lesions or cancer.

Experts caution, however, that the results of studies conducted in animals often are not replicated in humans.

"We believe that BPA actually reprograms the stem cells to be more sensitive to estrogen throughout life, leading to a lifelong increased susceptibility to diseases including cancer," Prins said.

The researchers said previous studies involving rodents have also shown that BPA, which acts like estrogen, is linked to several types of cancer, including prostate cancer. They added, however, that BPA, which is often used to soften plastics, is nearly impossible to avoid entirely.

"Previous studies have shown that people who avoided all contact with plastics or other BPA-containing objects for up to a month or more still had BPA in their urine, which means they must have come into contact with BPA in the last 24 to 48 hours, since it clears the body rather quickly," Prins said. "It's very hard to avoid."

More information

The U.S. Department of Health and Human Services provides more information on BPA.