A new study conducted by researchers at the Harvard School of Public Health has found that in subjects who ate canned soup for five days, levels of bisphenol A (BPA) found in the urine increased more than 1000%, compared to BPA levels in those who ate fresh soup for five days. BPA is a chemical that has been linked to obesity, cardiovascular disease and diabetes.
The new study, led by Jenny L. Carwile, doctoral student in epidemiology at the Harvard School of Public Health and senior author Karin B. Michels, ScD, PhD, a professor at Harvard Medical School, is published in the November 23-30, 2011 issue of JAMA, the Journal of the American Medical Association.
“Human exposure to bisphenol A (BPA) is widespread. In adults, urinary BPA concentrations are positively associated with cardiovascular disease and diabetes,” the Harvard researchers wrote in an introduction to their study report.
As authority for the widespread exposure of humans to BPA, the authors cited the National Report on Human Exposure to Environmental Chemicals, by the U.S. Centers for Disease Control & Prevention (CDC), with updated data and Tables as of February 2011.
In support of the positive association between BPA and cardiovascular disease and diabetes, the Harvard researchers site a study by UK and US scientists, Association of Urinary Bisphenol A Concentration With Medical Disorders and Laboratory Abnormalities in Adults, published in the September 16, 2008 issue of the Journal of the American Medical Association.
“Exposure [to BPA] occurs primarily through the diet. Bisphenol A has been quantified in many canned goods, where it is present as a by-product of interior epoxy coatings used to prevent corrosion,” the Harvard researchers wrote.
As noted by the researchers, a 2009 report by Consumer Reports, expressed concern over BPA exposure in canned foods. “Our tests find wide range of Bisphenol A in soups, juice, and more,” the Consumer Reports study headline announced. A video summary is included with the Consumer Reports findings.
The New Harvard Study – Method
Ms. Carwile and Dr. Michels designed their study to test the hypothesis “that canned soup consumption would increase urinary BPA concentrations relative to fresh soup consumption.”
They recruited 84 study participants among students and staff at Harvard, 75 of whom completed the study.
The participants were randomly assigned to two groups. For the first five days one group consumed a 12-ounce serving of canned vegetarian soup (from 18.5-ounce Progresso brand) at lunchtime each day, while the other group consumed the same quantity of fresh vegetarian soup (prepared without canned ingredients) at lunch each day. Through urine samples provided on days four and five of the trials, the level of BPA in the subjects’ urine were measured for all study participants.
After a two-day “washout” period, eating assignments for the two groups were reversed, and the same trials and BPA measurements were repeated for another five days.
While only Progresso brand soups were used as the canned soup in the trials, the study authors wrote that “generalizability to canned goods with similar BPA content is expected.”
Based on their analysis of the study results, the researchers found that the concentrations of BPA in participants’ urine were 1221% higher in those who consumed canned soup than in those who consumed fresh soup.
“Following canned soup consumption, SG-adjusted urinary BPA concentrations were, on average, 22.5 μg/L [micrograms per liter] higher (95% CI, 19.6-25.5 μg/L) than those measured after a week of fresh soup consumption (P < .001), representing a 1221% increase," the authors wrote.
The Harvard researchers pointed out some limitations in their findings:
However, the study authors noted that the extent of increase in BPA levels found after just five days of consuming canned soup was comparatively extreme.
“The absolute urinary BPA concentrations observed following canned soup consumption are among the most extreme reported in a nonoccupational setting. For comparison, the 95th percentile unadjusted urinary BPA in the 2007-2008 National Health and Examination Survey was 13.0 μg/L (95% CI, 10.0-15.4 μg/L),” the authors wrote.
Lead author Jenny Carwile told the Harvard Crimson, “The increase in BPA was surprising because we gave the candidates just one 12-ounce serving of soup per day.” She mentioned that she had previously conducted a study on consumption of liquids from polycarbonate water bottles, which found a 66% increase in BPA after water bottle use. “The results from the tests on the polycarbonate water bottles showed a much more modest association to BPA,” she said. “I was expecting something more on par with that.”
Conclusions & Implications
“The observed increase in urinary BPA concentrations following canned soup consumption, even if not sustained, may be important, especially in light of available or proposed alternatives to epoxy resins linings for most canned goods,” the authors of the new Harvard study concluded.
The U.S. Food and Drug Administration (FDA), since 2010 has been studying the health effects of BPA for the purpose of formulating new findings as to safe levels of exposure to BPA and new regulations of BPA.
In a FDA Public Health Announcement issued in January 2010, the FDA said, “FDA is supporting recommendations by the Department of Health and Human Services for infant feeding and food preparation to reduce exposure to BPA.” “With respect to uses of BPA in packaging of food intended for other populations,” the FDA wrote,
The complete report of the new Harvard study is available in the November 23-30, 2011 issue of JAMA, the Journal of the American Medical Association.
See also, the 2009 report by Consumer Reports, which expressed concern over BPA exposure in canned foods.