published Oct. 27, 2021, in JAMA Network Open.
In this multicenter cohort study, led by epidemiologist Shu-Li Wang, PhD, of the National Institute of Environmental Health Sciences, in Taiwan, each twofold increase in prenatal arsenic level correlated with a 2.4-fold higher rate of atopic dermatitis in 4-year-olds.
Atopic diseases have been on the rise. Eczema (atopic dermatitis) is the first stage of the so-called atopic march, followed by food allergies, allergic rhinitis, and asthma later in childhood. Previous research has linked heavy metal exposure to allergic diseases in adults. In another study by Dr. Wang and colleagues that was published in 2021, prenatal and early-life arsenic exposure was found to correlate with higher rates of allergic rhinitis and asthma in children. In that study, the participants were followed every 2-3 years through the age of 14 as part of the Taiwan Maternal and Infant Cohort Study.
The new study included 370 mother and child pairs who were enrolled in that birth cohort study between October 2012 and May 2015. During their third trimester of pregnancy, women completed questionnaires about their lifestyle, diet, and living environment. In addition, their height, weight, and blood pressure were recorded, and urine samples were taken. In follow-up interviews 3-4 years later, the mothers were asked whether their child had ever been diagnosed with atopic dermatitis.
The researchers used an inductively coupled plasma mass spectrometer to analyze the participants’ urine samples. They assessed for exposures in utero to eight metals: arsenic, cadmium, lead, cobalt, copper, nickel, thallium, and zinc.
Each unit increase of an index that estimates the combined exposure to these metals during pregnancy was associated with 63% higher odds of atopic dermatitis in the children by age 4. The researchers adjusted for parental allergies (yes or no), mother’s educational level (<12 years, 13-16 years, or >16 years), geographic area (central or eastern Taiwan), exposure to tobacco smoke during pregnancy, and the child’s gender. Arsenic (40.1%) and cadmium (20.5%) accounted for most of the metal coexposure index.
A wealth of previous research links arsenic exposure during adulthood to skin disease and immune dysfunction. Early-life arsenic exposure has been linked with elevated risk for various adult disorders, including cancer, diabetes, and heart disease, years later. In light of such research, “the findings in this paper are not surprising,” J. Christopher States, PhD, director of the Center for Integrative Environmental Health Science at the University of Louisville (Ky.), told this news organization. “Low-level arsenic exposure does not cause disease immediately, but it does appear to have long-lasting effects, making individuals susceptible to ‘second hits’ with another environmental agent.”
Research into the molecular mechanisms for these links has shown that arsenic and cadmium exposure can promote allergic phenotypes in immune cells. “We think the toxic metals activate the alarmin pathway, thus inducing innate lymphoid cells, then activating T-helper 2 cells, which drive immunoglobulin E production and breakdown of the epithelium and promotion of allergies,” said Kari Nadeau, MD, PhD, director of the Sean N. Parker Center for Allergy and Asthma Research at Stanford University. Dr. Nadeau led that study, published in 2017 in PLOS One, along with epidemiologist Margaret Karagas, PhD, of Geisel School of Medicine at Dartmouth, Hanover, N.H.
As for what pregnant women can do to minimize their exposure to heavy metals, “that is a difficult problem and primarily a function of where one lives,” said Dr. States.
Drinking water and food are major sources of arsenic exposure. Groundwater is naturally contaminated with arsenic deposits that seep in from bedrock, said Dr. States. The U.S. Environmental Protection Agency regulates arsenic levels in public drinking water that is supplied to more than a few thousand people. However, small water supplies and private wells are unregulated, he said, and having these water sources tested for arsenic or fitted with systems to reduce arsenic can be very expensive.
Among foods, rice can have high concentrations of arsenic, Dr. Karagas told this news organization. To minimize arsenic exposure through the diet, women can limit rice-based foods, according to a web-based tool developed by her and coworkers.
In addition, tobacco smoke is a major source of cadmium exposure and a moderate source of arsenic exposure, Dr. States noted. Women can reduce their exposure to these metals by avoiding tobacco and secondhand smoke.
The study was supported by grants from the National Health Research Institutes, Chung Shan Medical University Hospital, Taiwan Ministry of Science and Technology, and the Taiwan Environmental Protection Administration. The authors and quoted experts report no relevant financial relationships.
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