Study participants who drank for a week from polycarbonate bottles — the popular, hard-plastic drinking bottles and baby bottles — showed a two-thirds increase in their urine of the chemical bisphenol A (BPA), Harvard School of Public Health researchers have found.

Heating has been shown to increase the leaching of BPA from polycarbonate, so BPA levels might have been higher had participants drunk hot liquids from the bottles.

Exposure to BPA, used in the manufacture of polycarbonate and other plastics, has been shown to interfere with reproductive development in animals and has been linked with cardiovascular disease and diabetes in humans.

BPA is also found in dentistry composites and sealants and in the lining of aluminum food and beverage cans.