Risk from chemical in canned soup overstated

Behind the Headlines

Thursday November 24 2011

BPA levels in tinned soup are unlikely to cause harm

Canned food “could contain 1,000 times more of a controversial ‘gender bending’ chemical than fresh goods,” The Daily Telegraph has reported.

The news is based on a study looking at how eating canned soup increased people’s urine levels of Bisphenol A (BPA), a chemical compound used to coat the insides of food cans to prevent rust, as well as in plastic products.

In recent years BPA has been in the spotlight as some studies have suggested it could interfere with foetal and infant development, and possibly the action of certain hormones. BPA has also been banned from plastic baby bottles in the EU and Canada as a precautionary measure.

The study found that eating one serving of canned soup for five days was associated with a 1,200% increase in levels of BPA in the urine, compared to eating one serving of fresh soup daily. Although this does suggest that tinned soup could be a source of high levels of BPA, the research did not look at any possible health effects. Indeed, it is possible that high levels of BPA in the urine could mean that the body deals with this chemical by rapidly eliminating it.

The UK’s Food Standards Agency (FSA) has examined BPA extensively, and says that levels of the compound people would typically consume do not represent a risk to consumers. The FSA also points out that even at higher levels BPA is not a health concern, since it is rapidly absorbed and eliminated by humans. However, the agency will reportedly be looking at the study, to see if it has any implications for consumers.


Where did the story come from?

The study was carried out by researchers from the US Centers for Disease Control and Prevention, and the Harvard School of Public Health and Harvard Medical School, Boston. It was funded by a grant from the Allen Foundation, a US organisation supporting nutritional research. The study was published as a research letter in the Journal of the American Medical Association (JAMA).

The Daily Telegraph’s claim that all types of canned products could contain 1,000 times more BPA than fresh goods was misleading. Although it is probable that other canned products contain BPA, this study only looked at a particular brand of canned soup.

Also, the levels found in this study need to be viewed in context. Even though there was a much higher level of BPA in the tinned soup, the FSA has looked at the issue extensively and found that the level of BPA the public might typically ingest is well below a level that might cause any harm.


What kind of research was this?

This was a randomised crossover trial involving 84 volunteers, set up to examine whether canned soup consumption increased levels of BPA in the urine, compared to fresh soup consumption. The authors point out that human exposure to BPA is widespread, primarily through diet, and that in adults higher urinary BPA levels are associated with higher risk of cardiovascular disease and diabetes. It should be noted that studies in this area only found associations, not that BPA causes these illnesses.

BPA is found in many canned goods, where it is a by-product of the resins used to coat the inside of cans to prevent rust.


What did the research involve?

In 2010, the researchers recruited 84 student and staff volunteers aged over 18 from Harvard School of Public Health. The study volunteers were randomly divided into two groups. For the first five days, one group consumed a 12 ounce (355ml) serving of fresh soup daily, while the other consumed the same size serving of a particular brand of canned soup, sticking to the same schedule.

Participants were not restricted in what types of other food they ate during the study.

This was followed by a two-day ‘washout’ period to allow for any BPA intake to clear between treatments. The two groups of volunteers then switched their assignments, so that for the next five days, the initial group eating canned soup now ate fresh soup and vice versa.

Urine samples were collected between 3pm and 6pm on the fourth and fifth days of each phase. Urinary BPA concentrations were measured using specialised laboratory techniques, and validated statistical methods were used to analyse the results.


What were the basic results?

Of the 84 volunteers, 75 (89%) completed the study, of whom 68% were women. Their average (median) age was 27 years.

  • BPA was detected in 77% of samples after fresh soup consumption and 100% of samples after canned soup consumption.
  • The average concentration of BPA was given in micrograms, or ‘μg’. There are 1,000,000 μg in 1 gram. BPA concentration was 1.1 μg/L (after fresh soup consumption, and 20.8 μg/L after canned soup consumption.
  • Following canned soup consumption, average urinary BPA concentrations were 22.5 μg/L higher than those measured after a week of fresh soup consumption. This represented a 1,221% increase.


How did the researchers interpret the results?

The researchers say that consuming one serving of canned soup a day over five days was associated with a more than 1,000% increase in levels of urinary BPA. They say that the urinary BPA concentrations observed following canned soup consumption were ‘among the most extreme reported in a non-occupational setting’ (that is, outside situations where people work with BPA). By comparison, they report one recent US health survey as showing only 5% of people in a community sample had BPA levels over 13.0 μg/L.



This small, short-term study has found that eating canned soup for a week seems to be associated with a fairly dramatic ‘peak’ in BPA levels in the urine. Although this is of interest, it should be noted that the study did not look at whether a regular diet of canned soup or other canned goods would result in high long-term levels of BPA in the urine or whether they would have any long-term health effects.

Some points to consider about this study:

  • It only looked at one brand of soup so it is uncertain if the results apply to other brands and other tinned foods. The authors say they expect other canned goods with high levels of BPA to produce the same results.
  • It involved a selected population of staff and students at one school, so it is unclear if the results could be generalised to other groups.
  • The study does not look at any health impact from increased consumption of BPA or from the level consumed by people eating tinned soup is actually harmful.
  • The participants were not restricted in what else they could eat, so there is the possibility that their diet outside the trial may have influenced the results. However, given the large disparity between consumers of tinned and fresh soup, it does seem unlikely that this external food consumption was behind the result, but it could certainly have played a contributing role.

Nevertheless, the findings suggest that BPA can leach from cans into food, and will doubtless be studied further by scientists involved in monitoring the safety of food products.

The FSA says that BPA is known to have ‘weak oestrogenic effects’, as well as reproductive and developmental effects, and that it could be an ‘endocrine disrupter’ – a chemical that interacts with hormone systems. However, despite there being evidence that some wildlife species have been affected by endocrine disrupters, there is so far no conclusive evidence linking them to harmful effects on human reproductive health.

The FSA advice at present is that levels of BPA found in food are not considered harmful. The agency says that independent experts have worked out how much BPA we can consume over a lifetime without coming to any harm, and that the amount absorbed from food and drink is significantly below this level.

Independent studies have found that even when consumed at high levels, BPA is rapidly absorbed, detoxified and eliminated from the body, and therefore is not a health concern.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Eating canned soup 'poses a chemical risk'. BBC News, November 23 2011

Cans contain gender bending chemical. The Daily Telegraph, November 23 2011

Links to the science

Carwile JL, Ye , Zhou X, et al. Canned Soup Consumption and Urinary Bisphenol A: A Randomised Crossover Trial. 2011; 306:2218-2220.

Further reading

Food Standards Agency: The science underpinning the Agency’s policy on BPA (2010) (PDF, 60kb)


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