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Drink from plastic bottles can raise the body’s levels of a controversial ‘gender-bending’ chemical by more than two thirds, according to tests.

Experts have been concerned about the possible health effects of bisphenol A (BPA) - an everyday chemical used in many plastic food and drink containers and tins as well as clear baby bottles - which is officially classified as toxic in some countries.

A study found that participants who drank for a week from polycarbonate bottles showed a 69 per cent increase in their urine of BPA, which mimics the female sex hormone oestrogen.

Researchers did not say how much liquid was drunk per day. Researchers from Harvard School of Public Health studied 77 students, who had first undergone 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 them during the next week. Previous studies have suggested that high levels of BPA consumption are linked to birth defects, growth problems and an increased risk of heart disease and diabetes.

In particular there are fears that heating the bottles, as parents would do when warming their baby’s milk, causes the chemical to leak in potentially dangerous quantities into the liquid contained within.

The senior author of the latest study, 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 hormone gland-disrupting potential." Canada banned the use of BPA in polycarbonate baby bottles last year and some manufacturers have voluntarily eliminated it from their products.

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 in the body.

Previous studies had found that BPA could leach from polycarbonate bottles into their contents, but this study - published in US journal Environmental Health Perspectives - is the first to show the size of the corresponding increase in urinary BPA concentrations in humans.

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.’

(Agencies)