It’s been over a year since we discussed the Journal of the American Medical Association (JAMA) article on bisphenol-A (BPA), a high volume chemical used in plastic components of food and drinks packaging and found in 90% of all Americans screened for the chemical. It is also a chemical that disrupts the endocrine system, a complex chemical signaling system that coordinates the actions and responses of various tissues and organs. The JAMA article examined self report in adults of cardiovascular disease and diabetes (“has a doctor ever told you that you had . . . “) and measured liver enzyme levels in relation to urinary BPA metabolite excretion in a one third random sample of the National Health and Nutrition Examination Survey (NHANES). NHANES is a cluster sample of the US population performed on a 2 year cycle.
The JAMA article reported on the first time such a study had been done and it linked increased BPA excretion with heart disease, diabetes and liver enzyme elevations in subjects from the 2003-2004 NHANES cycle. Although based on a hypothesis from animal studies, associations like this can come up accidentally, so replication of the result is an important. Consequently the same research team looked at the same variables in the 2006-2008 NHANES cycle whose subjects were completely different than the previous one. They report their results in PLoS-ONE:
Methodology and Findings
A cross-sectional analysis of NHANES: subjects were n = 1455 (2003/04) and n = 1493 (2005/06) adults aged 18-74 years, representative of the general adult population of the United States. Regression models were adjusted for age, sex, race/ethnicity, education, income, smoking, BMI, waist circumference, and urinary creatinine concentration. Main outcomes were reported diagnoses of heart attack, coronary heart disease, angina and diabetes and serum liver enzyme levels. Urinary BPA concentrations in 2005/06 (geometric mean 1.79 ng/ml, 95% CI: 1.64 to 1.96) were lower than in 2003/04 (2.49 ng/ml, CI: 2.20 to 2.83, difference p-value = 0.00002). Higher BPA concentrations were associated with coronary heart disease in 2005/06 (OR per z-score increase in BPA = 1.33, 95%CI: 1.01 to 1.75, p = 0.043) and in pooled data (OR = 1.42, CI: 1.17 to 1.72, p = 0.001). Associations with diabetes did not reach significance in 2005/06, but pooled estimates remained significant (OR = 1.24, CI: 1.10 to 1.40, p = 0.001). There was no overall association with gamma glutamyl transferase concentrations, but pooled associations with alkaline phosphatase and lactate dehydrogenase remained significant.
Higher BPA exposure, reflected in higher urinary concentrations of BPA, is consistently associated with reported heart disease in the general adult population of the USA. Studies to clarify the mechanisms of these associations are urgently needed. (Melzer D, Rice NE, Lewis C, Henley WE, Galloway TS (2010) Association of Urinary Bisphenol A Concentration with Heart Disease: Evidence from NHANES 2003/06.
PLoS ONE 5(1): e8673http://www.plosone.org/article/info:doi/10.1371/journal.pone.0008673. doi:10.1371/journal.pone.0008673)
Translation: Average urinary BPA levels were lower in the later NHANES cycle but the relationship with heart disease was essentially the same as in the earlier one, meaning the result was confirmed in the independent data. The the evidence of increased report of diabetes was still visible although it just missed the 5% level of statistical significance in the later cycle but remained significant when both cycles were pooled. The liver enzyme data did not show in increase in the later cycle, although the pooled estimate remained significant. In magnitude, a 60 year old male in the highest urinary BPA level had a 45% increased risk of reporting he had been told by his doctor he had coronary disease.
We read these data as confirming the heart disease and diabetes findings while leaving the liver enzyme results discordant. This study adds weight to the earlier finding and raises red flags higher for this ubiquitous chemical. While we don’t know a great deal about the half life of BPA in humans, animal data suggests it may be relatively short, so the levels seen in NHANES are indicative of recent and ongoing exposure.
BPA is now out of baby bottles and Health Canada has declared BPA a toxic compound. So far the US FDA has not acted. But don’t worry:
The American Chemistry Council, an industry trade group representing BPA manufacturers, criticized the study and defended the safety of the chemical, which has been approved for use by regulatory bodies. ?The study itself does not establish a cause-and-effect relationship between BPA exposure and heart disease,? commented Steven Hentges, a spokesman for the group. (Martin Mittelstaedt, Globe and Mail)