A new study has reported that consuming canned soup temporarily increases urinary bisphenol A (BPA) to levels that would be considered potentially very harmful to health if they were sustained. The plasticizer bisphenol A, a known endocrine disruptor, has been shown to promote mammary tumor development in mouse models of breast cancer. Urinary concentrations of bisphenol A have been reported to be positively associated with cardiovascular disease and type 2 diabetes. Exposure to bisphenol A, which occurs mainly through the diet, is widespread. Bisphenol A has been found in various canned goods, where it is leached from the epoxy coatings used to prevent corrosion of the can interiors. The study was designed to investigate the impact of consuming canned soup compared to fresh soup on urinary levels of bisphenol A.

The randomized, blinded crossover trial included 75 healthy Harvard School of Public Health student and staff volunteers. Study participants were divided into two groups. One group consumed a 12 oz. serving of fresh soup (which was prepared without any canned ingredients) for lunch each day during a five-day period, followed by a two-day washout period (without any soup), followed by another five-day period during which the group members consumed canned soup for lunch. The second group followed the opposite schedule, starting with canned soup first. Five kinds of canned vegetarian Progresso soups (including tomato and minestrone) were used in the study, as well as five similar homemade soups. Participants were not aware of whether they were consuming canned or fresh soup during any given period. They were otherwise permitted to eat what they wanted during the study period. Urine samples were obtained during the late afternoon on the fourth and fifth days of each period during which soup was consumed. The two urine samples of each person were combined for each period to minimize intra-individual variations.

While 23% of urine samples from the homemade soup periods contained no detectable bisphenol A, all study participants were found to have bisphenol A in their urine after consuming canned soup for five days. Levels of bisphenol A increased nearly 20-fold on average after participants consumed canned soup. The adjusted average individual difference between urinary bisphenol A levels following canned compared to homemade soups was 22.5 mcg/L. The results were comparable for both groups (canned followed by homemade or homemade followed by canned soups). The levels of bisphenol A after consuming canned soup can be compared to recent data from the National Health and Nutrition Examination Survey, according to the authors, which indicated that the 95th percentile for urinary bisphenol A was 13.0 mcg/L. The authors comment that the rise in urinary bisphenol A following canned soup consumption was likely to have been temporary and that the effects of such intermittent peaks is unknown. In addition, all of the canned soup came from a single manufacturer and the results might have been different if other soup manufacturers had been included. The authors conclude, however, that the magnitude of the observed bisphenol A peaks is large enough to cause concern.

Comments regarding the study

Another recent study found that urinary levels of bisphenol A also decreased significantly when participants consumed only fresh foods and avoided all types of packaged foods (see Food Packaging and Bisphenol A and Bis(2-Ethylhexyl) Phthalate Exposure: Findings from a Dietary Intervention below). In addition to food cans, soda cans are often lined with plastic that contains bisphenol A. Bisphenol A is also used in manufacturing polycarbonate plastics used in making plastic baby bottles, water bottles, and clear plastic sippy cups. Bottles and other plastic products that incorporate polycarbonates might be marked with an embossed 7 on the base. Consumer protections with respect to bisphenol A are weak.

Studies using mice have consistently found that exposure to bisphenol A promotes mammary tumor development and growth. Mice exposed to bisphenol A are more susceptible to carcinogen-induced mammary tumors compared to unexposed mice. Bisphenol A promotes the growth (in a manner similar to estradiol) of tumors established by implanting mice with hormone receptor positive human breast cancer cells. Prenatal exposure of mice to relatively low levels of bisphenol A (easily reached through diet) alters mammary gland development in ways that increase the likelihood of subsequent tumor development.