Recent articles have been sounding the alarm with assertions that US citizens have two times more BPA in their urine than Canadians. In an article that compared the national studies, the author cited a number of possible differences between Americans and Canadians that she believed could account for the difference. One factor mentioned was thermal paper. However, thermal paper is unlikely to play a role in the differences observed between Americans and Canadians.
Could thermal paper account for the difference?
First, there is no indication that the use of thermal paper is substantially different in the US and Canada. BPA has been used in thermal paper since the 1960’s, though it came into more common use in the 1990s – so it is not a new phenomenon that has occurred exclusively in the US.
Second, health agencies in the US, Europe, Canada and the World Health Organization have determined that most of BPA exposure is from food sources; therefore BPA in thermal paper could not possibly result in doubling exposures. In fact, absorption through the skin is thought to account for only 1 percent of total BPA exposure.
Additionally, studies have demonstrated that the small amount of BPA that is absorbed through the skin is rapidly metabolized, similar to its metabolism for oral doses. So, dermal exposure poses no greater health concern nor results extended exposures.
What may account for the difference between Americans and Canadians
The Canadian Health Measures Survey (CHMS) and the US National Health and Nutrition Examination Survey (NHANES) have different methods for tracking and controlling for fasting, last urinary void, and the time of day of specimen collection. Since exposure to BPA is almost exclusively from food and BPA is rapidly excreted in the urine, differences in the methodology to account for these factors is likely to skew the data and make the variation between US and Canada seem more extreme.
In addition, the timeframe of the studies was different. US NHANES data was collected in 2003-2004. The Canadian Health Measures Survey data was collected in 2007-2009. The use of reusable polycarbonate water bottles declined over this period and could account for the lower levels of BPA in the later study.
What does this difference mean?
Even if you take the differences at face value, the difference is between 1.4 µg BPA/g creatinine (1.16µg/L urine) in Canadians to 2.6 µg/g creatinine (2.6µg/L urine) in Americans [a microgram (µg) is 0.000001g]. This different is incredibly small.
For comparison, the United States and Europe have adopted the standard that consumption of 50 µg/kg body weight/day is safe. That’s 300ug/day for someone who weighs 132 pounds and regulators have built in margins of safety to this figure.
A good effort putting this data into perspective can be found at the Huffington Post.