56. Association between maternal urinary speciated arsenic concentrations and gestational diabetes in a cohort of Canadian women (lay summary)

Ashley-Martin J, Dodds L, Arbuckle TE, Bouchard MF, Shapiro GD, Fisher M, Monnier P, Morisset AS, Ettinger AS. Environment International. 2018 Dec;121(Pt 1):714-720. doi: 10.1016/j.envint.2018.10.008

Arsenic (As) is a naturally occurring chemical element found throughout our environment that can enter groundwater through erosion and weathering of soils, minerals, and ores. Arsenic compounds are used in the manufacture of transistors, lasers, and semi-conductors, as well as in the processing of glass, pigments, textiles, paper, metal adhesives, ceramics, wood preservatives, ammunition, and explosives.  Arsenic exists in different chemical forms, which can be classified into two groups: organic arsenic and inorganic arsenic.  Dimethylarsinic acid (DMA), an organic arsenic compound, is most commonly found at low levels in fish and shellfish. Inorganic arsenic may be found at low levels in rice, ground water and some types of seaweed.

Gestational diabetes (GDM) may occur during pregnancy when a woman’s blood glucose levels become too high.  Her blood sugar usually returns to normal soon after delivery; however, if she has had GDM, then she is at increased risk for type 2 diabetes.

Some research, including a previous MIREC study of blood arsenic (Shapiro et al., 2015) has suggested that maternal total arsenic levels are associated with an increased risk of GDM.  However, the toxicity of specific forms of arsenic is uncertain.

In this study, organic and inorganic forms of arsenic were measured in 1st trimester urine from pregnant women in the MIREC Study.  Women with GDM were identified from medical records.

Among 1243 women who had a live, singleton birth and no previous history of diabetes, 4% had GDM.  As inorganic arsenic species were rarely detected in maternal urine, this study focused on the dimethylarsinic acid (or DMA, inorganic arsenic species).

Compared to women with the lowest levels of the DMA form of arsenic, women in the highest exposure group had, on average, a 3.5 times greater risk of GDM.   If the woman was carrying a male fetus, the association between DMA and GDM was almost 5 times greater in women with higher DMA levels in urine compared to women with the lowest levels of DMA.  If she was carrying a female fetus and had high exposure levels, her risk of GDM was about two times greater than women with the lowest exposure levels.

These results suggest a positive relation between exposure to certain arsenic forms and GDM, which may be particularly strong among women carrying a male fetus.  However, it is possible that the observed associations are due to unmeasured or correlated exposures.  Therefore further research is needed to analyze risks associated with inorganic and organic arsenic in pregnant women and to further investigate the potential modifying role of fetal sex on arsenic toxicity.

This study was led by researchers at Dalhousie University.