Eating even moderate amounts of canned soup significantly increases exposure to Bisphenol-A according to a new study published Tuesday in the Journal of the American Medical Association (JAMA).
The chemical BPA, suspected of causing damage to human health, is used in the interior lining of the vast majority of canned soups and vegetables.
For the study, researchers at the Harvard School of Public Health fed fresh soup made without any canned ingredients to a group of students and staff for five days in a row, and fed 12 ounces of canned soup to a second group for the same five days.
Researchers measured BPA urine concentrations in both groups, then after a two-day cleansing period, switched groups, feeding the canned soup to those who previously received the fresh soup, and vice versa. 75 volunteers participated in the small study.
The results showed that after consuming one can of soup per day for five days, BPA urine concentrations were approximately 13 times higher on average than after consuming non-canned soup.
A similar study published two years ago, also led by Jenny Carwile at the Harvard School of Public Health, found a 69% increase in BPA urine concentrations among Harvard students assigned with using polycarbonate plastic water bottles for one week.
Although BPA leaches into food and drink at room temperature, the higher rates found in canned soups and vegetables has to do with how they're manufactured, says Frederick vom Saal, Professor of Biological Sciences at the University of Missouri-Columbia.
"Canned vegetable products are all coated with BPA and they're sterilized in the can for hours at very high heat," explains vom Saal, "the problem is that BPA is heat sensitive in terms of breaking the bonds apart in the resin lining and releasing BPA into food."
A separate study released last month found a greater risk of behavioral issues like hyperactivity, anxiety, and depression among the daughters of mothers with elevated concentrations of BPA in their urine during pregnancy.
Still, that study shows a correlation, not causation.
John Rost of The North American Metal Packaging Alliance, which represents the canned foods industry, says the elevated BPA levels following consumption of canned soups only shows that people are well suited to metabolize the chemical, and get rid of it in urine.
"BPA does leave your system quickly and efficiently," says Rost. “Your body can handle it”.
Vom Saal points out that many chemicals leave the system at similar rates as BPA, but are able to greatly alter physiology - an example he gave was birth control pills that also are excreted in urine.
"In order for it to be in urine, it has to have gone through blood," explains vom Saal. "And when we look at serum levels of BPA in people we find free BPA in blood, and so have over a dozen other studies".
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