Cord Blood Vitamin D Linked to Air Pollution

Miriam E. Tucker

September 19, 2012

September 19, 2012 — Gestational exposure to urban air pollution may contribute to reduced vitamin D levels in offspring, the findings of a prospective French study of mother–child pairs suggest.

The first-ever population-based study to examine the role of prenatal exposure to air pollution on cord blood levels of vitamin D was carried out over the course of 27 months in 2 French cities, Poitiers and Nancy, in 375 mother–newborn pairs.

Associations between estimated maternal air pollution exposure and newborn serum 25-hydroxyvitamin D (25[OH]D) levels were significant in all trimesters, but especially so in the third, according to Nour Baïz, MSc, from the Institut National de la Santé et de la Recherche Médicale, Epidemiology of Allergic and Respiratory Diseases Department, Unité Mixte de Recherche, and the Medical School Saint-Antoine, Paris, France, and colleagues. The results were published online August 17 in the Journal of Clinical Endocrinology and Metabolism.

"Because 80% of intrauterine bone mineralization takes place during the last trimester and because vitamin D contributes to bone mineralization, fetal need for vitamin D increases and may be one reason for vitamin D decline in maternal blood supply, hence the potential importance of vitamin D supplementation of pregnant women, especially during the third trimester of gestation," the authors write.

Using modeling software, the investigators estimated 2 types of air pollutants at the study participants' home addresses: Particulate matter less than 10 μm in diameter (PM10) and nitrogen dioxide (NO2). Cord blood samples were collected at birth and analyzed for 25(OH)D levels.

After adjustment, log-transformed serum 25(OH)D decreased by 0.15 U for a 10 μg/m3 increase in NO2 pregnancy level (P = .047) and by 0.41 U for a 10 μg/m3 increase in PM10 pregnancy level (P = .037). The association was strongest for exposures during the third trimester, with P values of .0003 and .004, respectively.

Newborns born in Poitiers had higher 25(OH)D levels than those born in Nancy, which typically has more pollution and less sunshine. Those born in summer and autumn had higher 25(OH)D levels than those born in winter, and a low household income was associated with lower 25(OH)D levels.

It is not clear how in utero exposure to urban air pollutants might contribute to subsequent vitamin D deficiency in cord blood serum. High levels of air pollution, by reducing the amount of ultraviolet B solar radiation reaching the ground, could reduce cutaneous vitamin D synthesis. However, air pollution levels in this study were within current World Health Organization standards, Dr. Baïz and colleagues note.

Other potential mechanisms include a selective effect of the pollutants on maternal liver metabolism of vitamin D, a hampering of maternal intestinal absorption of vitamin D, or a decrease in vitamin D–binding protein in both mothers and newborns.

A follow-up of the children born in this study is underway to investigate the relationship between vitamin D deficiency in newborns and health outcomes.

The assessment of exposure to atmospheric pollutants was supported by a grant from the French Agency for Environment Security. Funding for the larger EDEN study, from which these data were a subset, came from the following: Fondation pour la Recherche Médicale, French Ministry of Research IFR program, Institut National de la Santé et de la Recherche Médicale Nutrition Research Program, French Ministry of Health Perinatality Program, French National Institute for Population Health Surveillance, Paris-Sud University, French National Institute for Health Education, Nestlé, Mutuelle Générale de l'Education Nationale, French-Speaking Association for the Study of Diabetes and Metabolism (Alfediam), and the National Agency for Research. The authors have disclosed no relevant financial relationships.

J Clin Endocrinol Metabol. Published online August 17, 2012. Abstract