Is Soup Toxic to Your Health?

Bisphenol A (BPA) is a plasticizer that is regarded as an endocrine disruptor that may be linked to  cardiovascular disease, diabetes, and liver abnormalities.  Commonly used in food can linings, Karin B. Michels, from Harvard School of Public Health (Massachusetts, USA), and colleagues assessed the urinary bisphenol A (BPA) levels of 75 healthy men and women, ages 18 years and older, who consumed homemade soup for five consecutive days, and then ate canned soup for another five days in a row.

Urinary levels of BPA averaged 1.1 mcg/L during the homemade soup segment, but reached 20.8 mcg/L during the canned soup segment.   Observing that: “The effect of such intermittent elevations in urinary BPA concentrations is unknown,” the team urges that: “Even if not sustained, [it] may be important, especially in light of available or proposed alternatives to [BPA-containing] epoxy resin linings for most canned goods.”

Recent data from the National Health and Nutrition Examination Survey, for example, indicated that the 95th percentile for urinary BPA was 13.0 mcg/L, Michels and colleagues noted.

BPA is used in a wide range of consumer and medical products to soften plastics. Studies have shown that BPA can mimic the action of female reproductive hormones and may be linked to cardiovascular disease, diabetes, and liver abnormalities. Infants’ exposure is a particular concern because they may be more sensitive to these effects than adults.

Last month, researchers found that children whose mothers had high urine levels of BPA during pregnancy were more prone to behavioral problems.

The U.S. government, after initially dismissing concerns about BPA in baby bottles and other consumer products, reversed course in 2010 and promised a major research effort to pin down the health risks.

Because BPA is also used in food can linings, Michels and colleagues sought to examine whether canned soups would be a vehicle to increase human intake of the chemical.

They used five varieties of vegetarian Progresso soups, including tomato and minestrone, and five similar homemade soups. Participants were randomly assigned to start with the commercial or homemade soups, eating a serving of each variety at lunchtime daily for five days. After a two-day washout period, participants who first ate the canned products then had a week of the homemade soups, and vice versa.

Participants could otherwise eat what they pleased during the study.

Urine samples were collected in the late afternoon on the fourth and fifth days of each period. To minimize intraindividual variations, each person’s samples from consecutive days were mixed prior to analysis.

BPA levels in urine were adjusted for dilution, using a formula that included the samples’ specific gravity.

All the participants had detectable BPA in their urine after eating the canned soup, whereas 23% of samples in the homemade-soup phase were BPA-free.

The mean individual difference between mean adjusted urinary BPA levels following canned versus homemade soups, 22.5 mcg/L, was highly significant, with a 95% confidence interval of 19.6 to 25.5 mcg/L, Michels and colleagues reported.

Results were nearly identical for participants who started the trial with canned soup compared with those initially assigned to the homemade soups.

The researchers did list several limitations to the analysis. The study involved one institution (all participants were students or employees of the Harvard School of Public Health) and the canned soup came from a single manufacturer.

More important, Michels and colleagues indicated that “the increase in urinary BPA concentrations following canned soup consumption is likely a transient peak of yet uncertain duration. The effect of such intermittent elevations in urinary BPA concentrations is unknown.”

But they argued that the magnitude of the peaks seen in their study is great enough to cause concern.

“Even if not sustained, [it] may be important, especially in light of available or proposed alternatives to [BPA-containing] epoxy resin linings for most canned goods.”