Morning melatonin serum values do not correlate with disease activity in rheumatoid arthritis: a cross-sectional study

Rheumatoid arthritis (RA), the most prevalent autoimmune arthritis worldwide, usually presents with a circannual manner and, meanwhile, follows a circadian rhythm for symptoms like morning stiffness. Therefore, association between RA and some hormones such as melatonin (MLT) and vitamin D, whose serum values are related to body circadian rhythms or seasonal variations, has become more noticeable recently. Since some studies proposed that RA patients show altered MLT circadian rhythms, especially in concordance with symptoms, in this research, we present the correlation between MLT serum values and RA disease activity score (DAS28ESR). The current cross-sectional study was carried out on 80 volunteers (60 patients and 20 healthy controls). Fifty percent of the participants in each group were sampled in cold, and the same percentage were sampled in warm seasons at 8 a.m. Disease activity was estimated utilizing DAS28ESR. Patients with possible known confounders of MLT secretion were excluded. A commercial MLT ELISA kit was employed to measure MLT. Statistical analysis was conducted by SPSS-11 software. This study outlined higher serum values of MLT in RA patients compared with controls (P = 0.006, z = −2.73). However, MLT did not correlate with DAS in patients (P = 0.45, r = −0.09). GLM analysis demonstrated that DAS28ESR, age, disease duration, medications, gender, and season of sampling had no influence on serum MLT. However, newly diagnosed RA patients presented higher MLT values than established ones (P = 0.03, t = −2.2). A cutoff point value of 23 pg/mL (63.3 % sensitivity and 90 % specificity) for MLT was computed between patients and controls. This study denoted that morning MLT serum values are higher in RA patients than in healthy volunteers. However, MLT and RA disease activity or other disease characteristics do not correlate. MLT serum values were higher in newly diagnosed RA patients than established ones.