BOSTON — Researchers at the Harvard School of Public Health found that participants who drank for a week from polycarbonate bottles showed a two-thirds increase in their urine of the chemical bisphenol A (B.P.A.). The study, according to its authors, is the first to show that drinking from polycarbonate bottles increases the level of urinary B.P.A.

The study consisted of 77 Harvard college students who began it with a seven-day period in which they drank all cold beverages from stainless steel bottles in order to minimize B.P.A. exposure. The participants provided urine samples during the seven-day period.

They were then given two polycarbonate bottles and asked to drink all cold beverages from the bottles during the next week. Urine samples also were provided during that time.

The results showed that the participants’ urinary B.P.A. concentrations increased 69% after drinking from the polycarbonate bottles.

"We found that drinking cold liquids from polycarbonate bottles for just one week increased urinary B.P.A. levels by more than two-thirds," said Karin B. Michels, associate professor of epidemiology at the Harvard School of Public Health and Harvard Medical School as well as senior author of the study. "If you heat those bottles, as is the case with baby bottles, we would expect the levels to be considerably higher."

One of the study’s strengths, according to the authors, is that the study participants drank from the bottles in a normal use setting. In addition, the students did not wash their bottles in dishwashers or put hot liquids in them. Heating has been shown to increase the leaching of B.P.A. from polycarbonate.