Prenatal exposure to phthalates and phenols and infant endocrine-sensitive outcomes: the MIREC Study (Lay summary)

Arbuckle TE, Agarwal A, MacPherson SH, Fraser WD, Sathyanarayana S, Ramsay T, Dodds L, Muckle G, Fisher M, Foster WG, Walker M, Monnier P. Environment International.2018 Nov 120:572-583. doi: 10.1016/j.envint.2018.08.034. 

Endocrine disrupting chemicals can interfere with hormone systems and produce adverse developmental, reproductive, neurological, and immune effects. The distance between the anus (external opening of the rectum) and the genitals in infants (anogenital distance) is one indicator of endocrine disruption.  Anogenital distance is used in animal studies to identify chemicals that are potentially toxic to the reproductive system. This has recently been measured in humans.  Another possible measure of endocrine disruption is the ratio between the length of the 2nd and 4th fingers (2D:4D).   These two measures are different in males and females. Males have longer anogenital distances than females, and in males the 2nd finger is usually shorter than the 4th, resulting in lower 2D:4D ratios.

Phthalates are used in plastics to soften and increase flexibility. They’re also used in many consumer products (e.g., hair spray, nail polish, shampoo).  Bisphenol A (BPA) is used to make a hard, clear plastic in many consumer products, such as reusable water bottles. It is also used as a protective lining inside metal food cans as well as on paper receipts. Triclosan is used as a preservative and antimicrobial in many cosmetic and consumer products. These chemicals may be able to disrupt the endocrine system.  A few studies have reported that prenatal exposure to elevated levels of some phthalates was associated with a shorter anogenital distance in male infants.

This study measured phthalates, bisphenol A and triclosan concentrations in urine of pregnant women from the MIREC Study.  In about 400 infants from this study, the distance between the anus and penis in boys and between the anus and clitoris in girls was measured, along with their finger length ratios.

Higher levels of two phthalates in maternal urine were associated with either a shorter anus-clitoris distance, or a longer one, depending on the chemical studied.  In male infants, higher urine levels of one kind of phthalate were associated with a longer anus-penis distance.  Female finger length ratio of the right hand was associated with higher levels of one type of phthalate and lower levels of BPA.

In conclusion, a few associations were observed between elevated maternal urinary concentrations of some phthalates and anogenital distance in infants.  However, these results were not consistent with other studies.  There were a large number of associations examined in this study, and so the few significant associations observed may be due to chance.  These inconsistencies suggest that the question of whether these chemicals affect anogenital distance, especially in males, has yet to be answered.