Hypertensive disorders during pregnancy are one of the main causes of maternal and child mortality and morbidity. Exposure to environmental chemicals is suspected to increase the risk of high blood pressure, but few studies have addressed the effect of non-persistent chemicals – those that linger only for a brief period into the body – particularly among pregnant women. A potential mechanism that could explain how these chemicals affect blood pressure is endocrine disruption. Once the chemicals enter in our organism through diet, skin or air, they reach the blood and can imitate the action of hormones. For example, BPA has estrogenic properties and estrogens are themselves known to have protective effect on arterial stiffness. Like estradiol (female hormone), BPA may increase production of nitric oxide (*NO), which is produced by the nitric oxide synthase (NOS) system of enzymes. Nitric oxide a bodily widespread mediator that is responsible for blood vessel enlargement (vasodilation). Nitric oxide (NO) is a key regulator of both maternal and fetal homeostasis during pregnancy, facilitating the maternal cardio-vascular changes, fetal development and growth and adaptation to extrauterine life.
Dysfunction of the NO system during pregnancy is associated to placental and vascular-related diseases such as hypertensive disorders of pregnancy (HDP) and intrauterine growth restriction (IUGR). Therefore, exposure to certain chemicals such as phthalates, parabens or Bisphenol A could be associated with a decrease in blood pressure during pregnancy. This is one of the main conclusions of a study led by the Barcelona Institute for Global Health (ISGlobal), and published recently in the International Journal of Hygiene and Environmental Health. This study, which is part of the HELIX project, followed 152 pregnant women from Barcelona (Spain), Grenoble (France) and Oslo (Norway). Three urine samples per day were collected during one week in the second trimester and one week in the third trimester, in order to measure exposure to 21 substances: ten phthalate metabolites, seven phenols including parabens and bisphenol A (BPA), and four organophosphate pesticide metabolites. Blood pressure was measured at the end of each week. The major strength of this study lied in its repeated and prospective design and the use of multiple bio-specimens per person.
The results show that a higher exposure to some phthalates, BPA and parabens were associated with a decrease in blood pressure, both systolic and diastolic, particularly in the second trimester, explains No association was found for pesticide exposure. BPA and phthalates are widely used in the manufacturing of consumer and medical products. Recent epidemiological and research studies have suggested that phthalate exposure adversely affects cardiovascular function; therefore, these chemicals represent a potential hazard for pregnancy. Dr. Charline Warembourg, ISGlobal researcher and first author, summarized the results: “Our findings do not support the hypothesis suggested by previous studies of a hypertensive effect of phthalates, phenols or pesticides during pregnancy. This apparent contradiction with studies in non-pregnant populations may reflect physiological changes that occur during pregnancy and modify blood pressure. Thus, non-persistent chemicals could actually enhance the decrease in blood pressure frequently observed in the first mid of the pregnancy. Another possible explanation is that the study did not cover the late pregnancy period, which is at risk for onset of hypertensive disorders”.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Scientific references
Warembourg C et al. Int J Hyg Environ Health 2018 Dec 27.
Canara A LR et al., Fraser WD. Am J Perinatol. 2018 Dec 14.
Lester F, Arbuckle T et al. Environ Int. 2018 Nov; 120:231-27.