Human serum paraben levels and their associations with rheumatoid arthritis: a case-control study from Hangzhou, China

Parabens are widely used in consumer products resulting in frequent exposure to humans. To date, little is known about the association between human paraben exposure and rheumatoid arthritis (RA). In this study, a case-control study (n = 290) was conducted in Hangzhou, China, aiming to quantify the concentrations of methyl paraben (MeP), ethyl paraben (EtP), propyl paraben (PrP), and butyl paraben (BuP) in serum samples and to determine their associations with RA risks. MeP (mean 4.7 ng/mL, range <0.05–20 ng/mL) was the predominant paraben in human serum, followed by PrP (1.9 ng/mL, <0.12–24 ng/mL), EtP (1.4 ng/mL, <0.09–10 ng/mL), and BuP (1.09 ng/mL, <0.10–10 ng/mL). With 1-unit increase of MeP concentrations in human serum, the levels of rheumatoid factors, anticyclic citrullinated peptide antibody, and immunoglobulin G will increase by 0.19 unit (95% confidence intervals [CI]: 0.12–0.46), 0.30 unit (95% CI: 0.26–0.58), and 0.24 unit (95% CI: 0.21–0.30) in the adjusted model, respectively. One-unit increase of MeP and PrP concentrations in human serum was associated with an increase of 0.15 (95% CI: 0.037–0.28) and 0.20 (95% CI: 0.10–0.32) in the C-reactive protein concentrations. In addition, an association between serum MeP levels and the incidence of RA (odds ratios (OR)_crude = 1.33, CI: 1.11–1.62, p = 0.03; OR_adjusted = 1.86, CI: 1.32–2.63, p = 0.02) was positive and significant. Based on the measurements of serum paraben concentrations, this work supports the evidence for the significant associations among paraben exposure, change of specific immune marker, and RA risks.