Exposure to the hormone-disrupting chemical Bisphenol A (BPA) has been underestimated, because prior lab tests have looked at single exposures rather than daily diets, the University of Missouri reports.

The study, released online Monday, is billed as the first to examine BPA concentrations in any animal after exposure through a steady diet, which mirrors the chronic exposure that humans receive through food packaging. The chemical, linked to breast cancer, heart disease, diabetes, male infertility and other health problems, is widely used in bottles and cups and in the linings of metal cans, including infant formula.

The UM scientists continuously exposed the mice to BPA through their feed and found a significantly greater increase in the active form of the chemical, which can bind to sex steroid receptors and exert adverse effects.

“When BPA is taken through the food, the active form may remain in the body for a longer period of time than when it is provided through a single treatment,” the study’s lead author Cheryl Rosenfeld, associate professor in biomedical sciences, said in a statement. She added:

We know that the active form of BPA binds to our steroid receptors, meaning it can affect estrogen, thyroid and testosterone function. It might also cause genetic mutations. Thus, this chemical can hinder our ability to reproduce and possibly cause behavioral abnormalities that we are just beginning to understand.

The study, published in Environmental Health Perspectives, says more than 8 billion pounds of BPA are produced every year, and more than 90% of U.S. residents have measurable amounts of BPA in their bodies. Its funding came from the National Institute of Environmental Health and Sciences.

An increasing number of U.S. states have been moving to ban BPA’s use in products aimed at young children, and some countries, including Canada, have already approved such bans. The U.S. Food and Drug Administration, in Jan. 2010, said it had “some concerns” about the chemical’s potential effects on brain development of fetuses, infants and children. It did not say BPA is unsafe.

Via its packaging, food is by far the main source of human exposure to BPA, according to the World Health Organization and the United Nation’s Food and Agriculture Organization. Less important sources, they said, are house dust, soil or toys, dental treatments and thermal papers such as cash register receipts.

Americans have twice as much of BPA in their bodies as do Canadians, but the reasons for the disparity remain a mystery, a Tufts University study in March concluded. The author, Laura Vandenburg, found the disparity in all age groups and noted, in both countries, that children and adolescents have the highest levels of BPA.

Another study released in March said adults and children can reduce their BPA exposure by eating more fruits and vegetables and less food from plastic containers and metal cans. A group of 20 San Francisco residents had 66% less BPA in their urine after spending three days on a diet of fresh, organic and unpackaged food, according to the Silent Spring Institute, a Massachusetts-based nonprofit that studies environmental factors in women’s health.