Ubiquitous bisphenol A linked to adult obesity, insulin resistance.

Jan 04, 2012

Wang, T, M Li, B Chen, M Xu, Y Xu, Y Huang, J Lu, Y Chen, W Wang, X Li, Y Liu, Y Bi, S Lai and G Ning. 2011. Urinary Bisphenol A (BPA) concentration associates with obesity and insulin resistance. The Journal of Clinical Endocrinology and Metabolism http://dx.doi.org/10.1210/jc.2011-1989.

Synopsis by Steven Neese

High urinary levels of bisphenol A in older adults are associated with increased weight and waist size, both indicators of obesity that can lead to serious illness and disease.

Researchers in China have found that adults over the age of 40 with higher levels of bisphenol A (BPA) in their urine tend to be obese, have more abdominal fat and be insulin resistant. These metabolic disorders can lead to further and more harmful health problems, such as high blood pressure, diabetes and heart disease.

Since BPA exposure is widespread – almost all people in the United States carry it in their bodies – the study's results highlight a potentially significant health risk from exposure to the contaminant.

BPA is a high-production chemical used in the manufacture of polycarbonate plastics, in epoxy resin linings of food cans and in some thermal receipt paper. The chemical can contaminate food and drink and enter the body through diet. BPA can also be absorbed through the skin or breathed in.

Prior epidemiological studies, published in the Journal of the American Medical Association and the journal PLoS One, have revealed links between BPA and metabolic disorders, consistent with this new research.

Previous lab-based studies correlate BPA to an increase in fat cells and increases in insulin hormone levels. These, in turn, can lead to hyperinsulinemia and insulin resistance and – perhaps – obesity. Exposures to this chemical in rodents during prenatal periods also alter the development of brain regions associated with food intake and metabolism. Hence the animal studies add to the plausibility of these new results from China.

In the study, BPA levels were measured in 3,390 adults older than 40 from the Songnan Community, Shanghai, China. Sociodemographic, medical and lifestyle backgrounds were collected from each person. Glucose and insulin levels were also measured.

Body mass indexes (BMI, the weight divided by height) were calculated for each person. "Overweight" was considered as a BMI from 24 to 28 while a BMI over 28 was considered "obese." Abdominal obesity was defined as a waist circumference more than 35 inches in men and 33.5 inches in women.

BPA was measured in a morning urine sample. The BPA levels were classified into groups by increasing concentration levels (from low to high), and the groups were compared. These levels where well within those typically seen in the United States.

The highest BPA levels were associated with both an obese BMI and waist circumference and higher concentrations of insulin in the blood. Overall, the younger men (average age of 59) in the study tended to have the highest levels of this chemical in their urine.

In participants with a BMI under 24, the prevalence of insulin resistance was increased by 94 percent in groups with the highest levels of this contaminant – an increase more prominent than in the obese BMI groups.

This study is limited by the fact that the relationship is based on a single sampling point of BPA and causality cannot be determined by the study's design – the researchers used a cross-sectional approach.

This study suggests that BPA levels in adults represent a health risk because they are related to obesity and related health problems.

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