Associations between mercury exposure and allergic diseases in children

In a recent study published in Scientific Reports, researchers assessed associations between mercury levels in urine and allergic diseases in children.

Study: Association between environmental mercury exposure and allergic disorders in Korean children: Korean National Environmental Health Survey (KoNEHS) cycles 3–4 (2015–2020). Image Credit: Tero Vesalainen/Shutterstock.com

Background

Environmental changes like air pollution and industrialized lifestyle habits cause immune system disruptions, leading to allergic diseases. Allergic disorders mainly occur in childhood and have a negative impact on the quality of life.

They are a public health concern, with considerable economic burden. Thus, identifying and managing risk factors of allergic diseases is crucial. Diet, exercise, genetic factors, climate change, pollution, and chemical exposure are identified as risk factors.

Heavy metals represent a significant concern as they build up in the body and do not easily break down. Mercury exposure occurs daily through fish, grains, and dental amalgams. Exposure to this heavy metal negatively affects the immune system.

Numerous studies have implicated mercury as a risk factor for allergic diseases. Nevertheless, the relationship between allergic diseases and mercury is inconclusive.

About the study

The present study assessed the association between urinary mercury levels and allergic rhinitis, asthma, atopic dermatitis, and multimorbidity in children.

Data from the third (2015-17) and fourth (2018-20) cycles of the Korean National Environmental Health Survey were analyzed. Participants were 6–11-year-old students susceptible to indoor allergens and air pollution exposure.

Participants with missing information were excluded. The team obtained urine samples on the day of the survey or a day before and estimated mercury levels.

Data on symptoms of allergic rhinitis, asthma, and atopic dermatitis were obtained through a questionnaire from participants’ guardians. They were asked to indicate the presence or absence of symptoms of the specified conditions and whether they were taking medicines.

Multimorbidity was defined as symptoms of more than one allergic disorder. Covariates were age, sex, parental education, body mass index (BMI), household income, and urinary cotinine and creatinine levels. Cotinine served as a biomarker for exposure to smoking.

Statistical analyses were performed using a complex sampling design. Data from the third and fourth cycles were separately analyzed.

Logistic regression was performed to examine associations between mercury levels and allergic diseases, and multinomial logistic regression was used for associations with multimorbidity.

One model was adjusted for creatinine levels; the second was adjusted for age and sex. The third model was adjusted for all covariates. Besides, fixed-effect models estimated the overall effect size in both survey cycles.

Findings

The researchers included 853 and 710 participants from the third and fourth survey cycles, respectively; their average age was approximately 8.5 years. The prevalence of allergic diseases was not significantly different between survey cycles.

The geometric mean of mercury levels in urine was 0.401 µg/L in the third cycle and 0.399 µg/L in the fourth cycle. There were no significant sex differences in mercury levels.

Urinary mercury levels were significantly higher when creatinine and cotinine levels were elevated. Students with symptoms of atopic dermatitis showed higher mercury levels than those without.

Urinary mercury levels were positively correlated with atopic dermatitis in both cycles, adjusted for creatinine levels. Mercury levels were positively associated with asthma, atopic dermatitis, and multimorbidity in both cycles, adjusted for all covariates.

Results were similar when pooled effects were calculated using data from both cycles; significant positive correlations with multimorbidity and atopic dermatitis were evident. In sex-stratified analyses, pooled effects on multimorbidity and atopic dermatitis were greater in males.

Moreover, the positive association between mercury levels and multimorbidity was only significant in males.

Conclusions

In sum, the present study investigated associations between mercury levels in urine and allergic diseases in elementary school students. The researchers observed a positive association between urinary mercury levels, atopic dermatitis, and allergic rhinitis.

Of note, they could not determine causality given the cross-sectional nature, warranting additional studies.

The questionnaire-based symptom assessment may not necessarily imply disease status. Moreover, data on long-term indicators (of mercury exposure) and parental allergy history were not considered.

Taken together, the study identified associations with sufficient statistical power, providing reliable evidence that mercury exposure is associated with allergic disorders in children.