WASHINGTON, Nov 22, 2011 (AFP) - People who ate canned soup for five days straight saw their urinary levels of the chemical bisphenol A spike 1,200 percent compared to those who ate fresh soup, US researchers said on Tuesday.

The randomized study, described as "one of the first to quantify BPA levels in humans after ingestion of canned foods," was done by Harvard University researchers and appears in the Journal of the American Medical Association's November 23 issue.

"We've known for a while that drinking beverages that have been stored in certain hard plastics can increase the amount of BPA in your body," said lead author Jenny Carwile, a doctoral student in the Department of Epidemiology at Harvard School of Public Health.

"This study suggests that canned foods may be an even greater concern, especially given their wide use."

The chemical BPA is an endocrine disruptor that has been shown to interfere with reproductive development in animal studies at levels of 50 micrograms per kilogram of body weight and higher, though it remains uncertain if the same effects cross over to humans, according to the Environmental Protection Agency.

This study did not measure BPA levels by micrograms per kilogram of body weight, but rather by micrograms per liter of urine, so a direct comparison to the EPA-cited danger level in animals was not possible.

However, previous studies have linked BPA at lower levels than those found in the Harvard study to cardiovascular disease, diabetes and obesity in humans, Carwile told AFP in an email.

BPA is found in the lining of canned foods, cash register receipts, dental fillings, some plastics and polycarbonate bottles marked with the number 7.

Seventy-five people took part in the study, eating a 12-ounce serving of either fresh or canned soup for five days in a row. They were advised not to otherwise alter their regular eating habits.

After a two-day break, the groups switched and ate the opposite type of canned soup.

A urine analysis showed the canned soup eaters had 1,221 percent higher levels of BPA than those who ate the fresh soup.

BPA is typically eliminated in the urine and so any spike is usually considered temporary. The researchers did not measure how long elevated BPA stayed in the body, saying more study would be needed to examine that question.

The US government's health and environmental agencies are considering whether "further action is needed to address human health risks resulting from non-food-packaging uses of BPA," according to the EPA.

France's Agency for Food Health Safety (Anses) in September called for tougher preventive measures, warning that even "low doses" of the chemical had had a "confirmed" effect on lab animals and a "suspected" effect on humans.

Preventing exposure to BPA among infants, pregnant or nursing women was a "priority goal," Anses said.

Meanwhile, the Harvard study authors said their findings should encourage people who eat a lot of canned foods to opt for fresh instead, and should serve as a red flag to manufacturers who use BPA to make cans.

"The magnitude of the rise in urinary BPA we observed after just one serving of soup was unexpected and may be of concern among individuals who regularly consume foods from cans or drink several canned beverages daily," said senior author Karin Michels.

"It may be advisable for manufacturers to consider eliminating BPA from can linings."