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.’

研究顯示，飲用塑料瓶裝水可使人體內頗具爭議的“性別偏移”化學物質含量提升超過三分之二。

專家對雙酚A（BPA）可能對人體健康造成的影響表示擔憂，這是很多食品和飲料塑料包裝盒、易拉罐、以及透明奶瓶中所含的常規化學成分，而一些國家已將該物質正式列為有毒物質。

研究顯示，被調查者飲用PC（聚碳酸酯）塑料制成的瓶裝水一周后，尿液中BPA的含量會增加69%，而BPA類似于雌性激素。

研究人員沒有闡明被調查者每天喝多少液體。來自哈佛公共衛生學院的研究人員對77名學生進行了調查，這些被調查者首先要進行為期一周的“沖洗”，在此期間，為盡量不接觸BPA，他們只能喝不銹鋼水瓶裝的冰飲料。

之后研究人員給被調查者兩個PC塑料瓶，并要求他們在接下來的一周內，只用這種水瓶喝冰飲料。此前研究已證實，BPA攝入量高與出生缺陷、發育問題以及心臟病和糖尿病患病風險高有聯系。

特別需要指出的是，加熱塑料瓶會造成更大危害。例如當家長使用塑料瓶給寶寶熱牛奶時，有一定量的潛在危險性化學物質會滲透進瓶內液體中。

該項最新研究的資深作者、哈佛公共衛生學院和醫學院的流行病學副教授卡利文•B•米歇爾說：“我們發現，使用PC塑料制造的水瓶喝冷水僅一周，尿液內的BPA含量就會增長超過三分之二。”

“我們認為，當你加熱塑料瓶，比如熱牛奶時，這種物質的含量會相當高。BPA有可能擾亂腺體激素分泌，嬰兒對此極其敏感，因此我們對此應更加注意。”加拿大于去年禁止在生產PC塑料奶瓶時使用BPA，一些制造商主動從產品中去掉了該成分。

大多數成年人體內都攜帶有BPA，但對于該物質的危害性，專家的看法卻有分歧。歐洲食品安全局稱，人體會將該化學物質自動轉化為危害較小的物質。

此前研究證實，BPA可以從PC塑料瓶體滲入所裝液體內，但發表在《美國環境衛生展望》期刊上的這份研究首次證實了（使用PC塑料瓶飲水后）人體尿液中BPA濃縮物增加的對應含量。

哈佛大學研究人員珍妮•卡維爾說：“此前研究已證實BPA對健康有副作用，而這項研究填補了這種推斷的空白---也就是PC塑料瓶是否是人體內BPA含量增高的罪魁禍首。”