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Is it safe to eat canned foods?

That's a question worth asking after a new study found a huge spike in urinary levels of the chemical bisphenol A – commonly known as BPA – in a group of volunteers who ate canned vegetable soup for several days. BPA, which has been linked to a variety of health disorders, is used in the lining of many food and beverage cans.

The results suggest BPA is being absorbed by the canned food and then ingested by consumers.

"We were very surprised by the numbers," said the senior author of the study, Karin Michels of Harvard Medical School in Boston. "It makes you feel a little uneasy about cans."

The experiment involved 75 participants. Half of them were asked to eat a 12-ounce bowl of canned vegetable soup at lunch for five consecutive days. After a two-day break, they consumed the same-sized serving of fresh vegetable soup for five lunches in a row. The other volunteers did the experiment in the reverse order – starting with five days of fresh soup, followed by five lunches of canned soup.

Urine samples were collected on several occasions, usually a few hours after the noon-time meal.

The analysis revealed that when participants ate the canned soup they experienced more than a 1,000 per cent increase in their urinary concentrations of BPA, compared to when they dined on fresh soup.

The study, published this week in the Journal of American Medical Association, represents one of the first attempts to measure BPA urine levels soon after the consumption of canned foods.

Even so, the study raises more questions than it answers. Because all urine samples were collected the same time of day, the researchers can't say how high the BPA levels rose. Nor can they say how quickly the BPA was excreted from the body. Plus, a lot more research is needed to determine the long-term health effects from this type of exposure.

Although the team investigated only canned vegetable soup, the researchers suspect they would find similar results with other canned food and possibly canned beverages as well.

"It would be interesting to see if a similar spike arises with soda because some people drink a lot of canned soda during the day," said Dr. Michels. "And if that's the case, you may have continuously elevated levels of BPA."

Scientists have warned that BPA could interfere with numerous biological processes because its structure resembles the hormone estrogen. It has been shown to interfere with reproductive development in animals and it has been linked to cardiovascular disease, diabetes and obesity in humans. Aside from cans, it's also used to make some hard, clear plastics, dentistry composites and sealants, and some cash register receipts.

The lead researcher, Jenny Carwile, a doctoral student at Harvard School of Public Health, noted that because BPA is used in the liners of most canned foods and beverages it can be hard to avoid. "I would love to see more BPA-free alternatives on the market to give people some options," she said.

Many manufacturers have already removed BPA from their plastic refillable liquid containers in response to consumer concerns. Dr. Michels conducted earlier research that indicated drinking liquids from containers made with the chemical could almost double urine levels of BPA. Her new study suggests canned foods could result in a far greater BPA burden on the body.