18. Exposure to phthalates, bisphenol A and metals in pregnancy and the association with impaired glucose tolerance and gestational diabetes mellitus: the MIREC study (lay summary)

Shapiro GD, Dodds L, Arbuckle TE, Ashley-Martin J, Fraser WD, Fisher M, Taback S, Keely E, Bouchard MF, Monnier P, Dallaire R, Morisset A, Ettinger AS. Environment International. 2015 Oct;83:63-71. doi: 10.1016/j.envint.2015.05.016

Over the past 20 to 30 years, the incidence of diabetes mellitus has been steadily rising in the Canadian population (and in other countries as well). People with diabetes either have a total lack of insulin (type 1) or they have too little insulin or cannot use it effectively (type 2) which results in abnormally high levels of glucose (sugar) in their blood. Too much glucose can lead to serious health problems. Gestational diabetes is a condition where women without previously diagnosed diabetes exhibit high blood glucose (blood sugar) levels during pregnancy.

Studies from several countries have also reported increases in the frequency of gestational diabetes. Previous research has suggested that prenatal exposure to certain environmental chemicals may be a contributing factor in the development of this disease by interfering with specific hormones involved in glucose metabolism.

This study, led by researchers at the Izaak Walton Killam (IWK) Health Centre in Halifax, used data collected in the MIREC Study to investigate the possible role of prenatal exposure to phthalates, bisphenol A (BPA), and metals in the onset of gestational diabetes and impaired glucose tolerance (a less severe glucose disorder). [BPA is used to make polycarbonate, a hard, clear plastic, and may also be found in linings on the inside of metal-based food and beverage cans, and thermal papers such as receipts. Phthalates, often called plasticizers, are commonly used to make plastics soft and flexible and harder to break].

Women in the MIREC cohort were included in this study if they had a singleton birth and did not have pre-existing diabetes. Of the 2,001 women recruited into the MIREC cohort, 1,274 met these criteria. Eleven phthalates and BPA were measured in the women’s first-trimester urine samples, and four metals (lead, cadmium, mercury and arsenic) were measured in first-trimester samples of the women’s blood. Results of a glucose tolerance test administered between 24 and 28 weeks of pregnancy were used to identify those women with gestational diabetes or with impaired glucose tolerance. The analysis of chemical levels and these health outcomes was adjusted for other factors such as maternal age, race, pre-pregnancy body mass index (BMI), and education, any of which could potentially influence the results.

The researchers found that women with the highest levels of arsenic in their blood were almost four times as likely to have gestational diabetes as women with the lowest blood levels of arsenic. No significant associations were observed between the other metals, phthalates, or bisphenol A and a higher risk of gestational diabetes or impaired glucose tolerance.

The findings from this study add to growing body of evidence supporting the potential role of arsenic in the development of gestational diabetes.