Scientists have demonstrated for the first time that the plastic bottles, so many of us drink soft drinks and bottled water from, release the chemical bisphenol A (BPA) into liquid stored in them.

BPA has been shown to interfere with reproductive development in in humans and animals and has been linked with cardiovascular disease and diabetes in humans. The chemical is found in plastic bottles of all kinds and the lining of metal cans in canned products and the lids of jars including baby food jars. This danger has been know for many decades but has been actively covered up by the packaging industry.

New research by Harvard School of Public Health found that participants who drank for a week from polycarbonate bottles showed a two-thirds increase of BPA in their urine.

Experts warned that babies are at greater risk, because heating baby bottles increases the amount of BPA released, and the chemical is potentially more harmful to infants.

Study author Karin B. Michels, associate professor of epidemiology at HSPH and Harvard Medical School, said: "We found that drinking cold liquids from polycarbonate bottles for just one week increased urinary BPA levels by more than two-thirds.
"If you heat those bottles, as is the case with baby bottles, we would expect the levels to be considerably higher.
"This would be of concern since infants may be particularly susceptible to BPA's endocrine-disrupting potential."

Altogether 77 students took part in the study after a seven-day "washout" phase in which they drank all cold beverages from stainless steel bottles in order to minimise BPA exposure.

They were then given two polycarbonate bottles and asked to drink all cold beverages from the bottles during the next week.

The results showed the volunteers' urinary BPA concentrations increased 69 per cent after drinking from the polycarbonate bottles.

Previous studies had found that BPA can be transferred from polycarbonate bottles into their contents, but this study is the first to show a corresponding increase in urinary BPA concentrations in humans.

One of the study's strengths, said the research published in Environmental Health Perspectives, is that the students drank from the bottles in a normal way.

Additionally, the students did not wash their bottles in dishwashers or put hot liquids in them, as heating has already been shown to increase the leaching of BPA from polycarbonate.

Canada banned the use of BPA in polycarbonate baby bottles in 2008 and some manufacturers have voluntarily eliminated BPA from their products.

With increasing evidence of the potential harmful effects of BPA in humans, the study's authors believe further research is needed into BPA's impact on babies, and on reproductive disorders and breast cancer in adults.

Most adults carry BPA in their bodies, but expert opinion on the risks is divided.
The European Food Safety Authority believes that people naturally convert the chemical into less harmful substances into the body.

Harvard researcher Jenny Carwile said: "While previous studies have demonstrated that BPA is linked to adverse health effects, this study fills in a missing piece of the puzzle – whether or not polycarbonate plastic bottles are an important contributor to the amount of BPA in the body."

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