Background: Arthritis and rheumatoid arthritis are highly prevalent among U.S. adults, but, the cause of the disease remains unknown. Identified risk factors for developing arthritis include age, sex, genetics, smoking, history of live births, obesity, and environmental factors. Exposure to mercury and other heavy metals has been associated with autoimmune diseases, but the association between mercury and arthritis is underexplored.
Goal: Using data from the 2013-2014 National Health and Nutrition Examination Survey (NHANES), this project will determine if adults with arthritis have higher levels of blood methyl mercury compared to healthy adults.
Objectives: • Determine the odds that an adult with arthritis will have higher levels of blood methyl mercury compared to adults without arthritis. • Determine the odds that an adult with rheumatoid arthritis will have higher levels of blood methyl mercury compared to adults without rheumatoid arthritis. • Establish whether gender, age, race, or BMI are confounding variables.
Approach: A secondary data analysis of the NHANES 2013-2014 was performed for adult participants who were at least 20 years of age, and had arthritis and blood methyl mercury data (n=2695). Weighted multiple logistic regression models were used to explore the association between arthritis/rheumatoid arthritis and blood methyl mercury levels while considering potential confounders.
Results: The weighted geometric mean blood methyl mercury levels for healthy adults, all adults with arthritis, and adults with rheumatoid arthritis are 0.91, 0.86, and 0.76 ug/l, respectively. After adjusting for age and obesity, the odds of adults reporting arthritis increased by 44% for every unit increase in log methyl mercury (95% CI = 1.13-1.84). The odds of adults reporting rheumatoid arthritis increased by 126% for every unit increase in log methyl mercury (95% CI = 1.29-3.95) after adjusting for age.
Importance to public health: Based on this cross-sectional analysis, exposure to methyl mercury was found to be positively associated with arthritis and rheumatoid arthritis. Future studies should consider a different study design to establish temporality.