Adults who ate canned soup daily showed a jump in levels of the plasticizer BPA in their urine, according to a small study.

The study of 75 people in Tuesday's issue of the Journal of the American Medical Association is one of the first to quantify BPA levels in humans after eating canned foods compared with eating freshly prepared ingredients.

Bisphenol A is an industrial chemical used to make polycarbonate plastic for water bottles and food containers as well as the protective lining in metal cans.

Previously, Health Canada focused on removing BPA from baby bottles to reduce exposure in newborns and infants. In August, Statistics Canada reported that more than 90 per cent of Canadians aged six to 79 had detectable levels of BPA in their urine.

The health risks of BPA in humans are unclear. Animal studies suggest that once ingested, BPA may imitate estrogen and other hormones, according to the U.S. National Institutes of Health. In the study, volunteers ate either canned soup or fresh soup daily for a week and then switched to the other type. Reuters

In the new study, Jenny Carwile, a doctoral student in the department of epidemiology at Harvard School of Public Health, Prof. Karin Michels, and their co-authors randomly assigned volunteers to eat a 340-gram serving of canned vegetarian soup in different varieties every day at lunch for five days.

After waiting two days, the same participants repeated the lunch assignment with the same amount of fresh soup that was prepared without any canned ingredients or vice-versa.

1,000 per cent increase

The average concentration of BPA was 1.1 micrograms per litre after fresh soup compared with 20.8 micrograms per litre after canned soup consumption, the researchers found.

In the Statistics Canada survey, average BPA levels in urine were 1.16 micrograms per litre.

"Consumption of one serving of canned soup daily over five days was associated with a more than 1,000 per cent increase in urinary BPA," the study’s authors concluded.

"Generalizability is limited due to selection of participants from one school and testing of a single soup brand; however, generalizability to canned goods with similar BPA content is expected."

Michels and her team noted that the effect of such short-term increases in urinary BPA levels is unknown.

The average age of the participants was 37 and 68 per cent were women.

When Health Canada studied BPA levels in canned goods from one store in Ottawa in April 2009, it concluded that on average, the BPA levels observed in the vast majority of samples were "not considered to represent a human health concern."

The North American Metal Packaging Alliance, (NAMPA) which represents soup makers, cited the Health Canada findings in criticizing the JAMA study.

"The presence of BPA in the urine does not indicate a health risk," NAMPA said in a statement, adding the finding confirms that BPA is quickly excreted.

"Government regulatory authorities, which are much more familiar with the benefits of epoxy resins and the limitations of alternatives for most canned goods, have consistently concluded that current exposures through canned foods do not pose a health risk to consumers, including newborns and infants."

Rick Smith, executive director of the advocacy group Environmental Defence, which was at the forefront of the fight against Bisphenol A, called the new study important.

"There's now an accumulation of evidence, scientifically rigorous evidence, that BPA in tin can lining is a problem," Smith said.

The Canadian and U.S. regulatory studies also showed BPA is readily excreted, but people are re-exposed on a daily basis, he said.

Smith called on the federal government to expedite its efforts to get the food industry to dramatically bring down BPA levels in canned food, noting some food companies are already taking BPA out of canned goods, even without government regulation.

With files from CBC's Lorenda Reddekopp