6. A birth cohort study to investigate the association between prenatal phthalate and bisphenol A exposures and fetal markers of metabolic dysfunction (lay summary)

Ashley-Martin J, Dodds L, Arbuckle TE, Ettinger AS, Shapiro G, Fisher M, Morisset AS, Taback S, Bouchard MF, Monnier P, Dallaire R, Fraser WD. Environmental Health. 2014;13:84. doi: 10.1186/1476-069X-13-84

Metabolic dysfunction is a term used to describe an impairment in how the body uses and stores energy and can be associated with higher rates of obesity and diabetes. Obesity and type-2 diabetes have been steadily rising in the Canadian population (and in other countries as well), and it is suspected that prenatal exposure to environmental contaminants is a contributing factor. These two diseases are metabolic in nature, affecting both fat metabolism and carbohydrate (sugar) metabolism. A feature common to both these metabolic processes is the involvement of specific hormones. Certain environmental contaminants, such as bisphenol A (BPA) and phthalates, can potentially disrupt these hormones and are thus referred to as “hormone (or endocrine) disruptors”. BPA is used to make a hard, clear plastic and may also be found in epoxy resin linings on the inside of metal-based food and beverage cans. Thermal papers such as receipts and tickets may also be a source of BPA. Phthalates are a family of chemicals commonly used to make plastics soft and flexible and harder to break. They are often called plasticizers and have a large number of industrial and commercial uses – for example, vinyl flooring, adhesives, detergents, automotive plastics, some children’s toys, and personal-care products (soaps, shampoos, hair spray, nail polishes). Some phthalates are also used as solvents for other materials. Given the widespread use of BPA and phthalates, the Canadian public has become increasingly aware of the presence of these chemicals in the environment, and there is growing concern about their possible negative health effects.

This research was conducted using the MIREC Study to look at relationships between prenatal exposure to BPA and phthalates, and biomarkers of metabolic dysfunction in the infants of pregnant women. (A biomarker is any measurable substance in an organism that can be used as an indicator of a particular disease state, environmental exposure, or some other physiological state). Two specific hormones – leptin and adiponectin – were measured in 1,363 samples of umbilical cord blood. Low levels of adiponectin and high levels of leptin may be associated with metabolic dysfunction.

Urine samples were collected from the pregnant women in their first trimester and analyzed for BPA and 11 phthalate metabolites. Chemicals such as phthalates can be absorbed into the body, then broken down (metabolized) and excreted in urine as metabolites. The researchers then assessed the relationship between phthalate and BPA levels in mother’s urine and levels of adiponectin and leptin in umbilical cord blood.

The results showed that leptin levels in cord blood were higher among female than male infants, while adiponectin levels were approximately the same among males and females. When compared to low exposure levels, moderate levels of the phthalate metabolite MCPP in urine was associated with a higher risk of having elevated cord blood leptin levels in male infants. No significant trends in associations were observed for any of the other chemicals examined.

This research suggests that exposure to some common environmental chemicals during pregnancy may have an impact on fetal hormone levels that may be associated with metabolic function. Further research needs to be done, however, to examine whether these changes in hormone levels are associated with changes in childhood growth, leading to obesity and/or type-2 diabetes later in life.