A controversial chemical found in plastic bottles, soda cans and many other common products appears to adversely affect sperm in men, according to new research.

The study of more than 200 Chinese factory workers found that those who were exposed to bisphenol A, or BPA, were more likely to have lower sperm counts and poorer sperm quality. The study, published in the journal Fertility and Sterility, is the first to produce evidence that the chemical could adversely affect sperm quality in humans.

"This adds additional human evidence that BPA is bad," said De-Kun Li, a reproductive and perinatal epidemiologist at Kaiser Permanente's Division of Research in Oakland, Calif., who conducted the study with funds from the National Institute of Occupational Safety and Health. "The general public should probably try to avoid exposure to BPA as much as they can."

The study is the third in a series of reports Li has published examining the effects of BPA exposure among Chinese factory workers. The two previous papers produced evidence that BPA exposure was associated with erectile dysfunction and other sexual problems in men.

BPA is found in thousands of consumer products, ranging from dental sealants to canned food linings. It is so ubiquitous that it has been detected in the urine of more than 90 percent of the U.S. population. Concern about the substance has been increasing as evidence has accumulated, primarily in laboratory animals, that it may be associated with health effects including infertility, weight gain, behavioral changes, premature puberty and diabetes.

After long maintaining that BPA is safe, the Food and Drug Administration in January reversed itself, saying it was concerned about the compound's health risks, especially in the development of fetuses, infants and young people.

In the meantime, many manufacturers have pledged to take BPA out of baby bottles, water bottles and other products, and a handful of jurisdictions across the country have banned BPA from baby products.

In the new study, Li and his colleagues found that those with detectable BPA levels in their urine were two to more than four times as likely to have poor semen quality, including low sperm concentration, low sperm counts, fewer sperm that were alive and more sperm that did not move normally, known as poor sperm motility. BPA was not associated with lower sperm volume or deformed sperm.

Steven G. Hentges of the American Chemistry Council said the workers in the study had been exposed to far higher BPA levels than any American would receive.

"What is important for consumers to know is that government agencies worldwide have examined the science on BPA, including a recent European Food Safety Authority review of 800 studies, and have concluded that low doses of BPA are not a risk to human health," Hentges said in a statement. "This study of Chinese workers with high exposure to BPA is of limited relevance to consumers who, by contrast, are exposed to only very low levels of BPA."

Li acknowledged that many of the study subjects worked in factories that produced BPA or used it to make resins, exposing them to levels far higher than any person would typically receive. But BPA appeared to affect sperm even at levels roughly equivalent to exposures that would be found in the U.S. public, he said.

"The higher your exposure, the lower your sperm quality is," he said.

The study included too few subjects to determine whether the effects made any men infertile, Li said. But the effect was sufficient for BPA to potentially affect fertility, either alone or combined with other factors that might adversely affect sperm, Li said. In addition, the findings suggest BPA could have other adverse health effects, such as increasing the risk of prostate cancer.