Sunlight–derived vitamin D affects interleukin-4 level, T helper 2 serum cytokines, in patients with Graves’ disease: a prospective cohort study

Background: graves’ disease (gd) is the most common autoimmune disease leading to hyperthyroidism. the role of th1/th2 pathways balance in gd is still controversial. vitamin d is reported to have an effect on those pathways. this study aims to examine the effect of sunlight exposure on vitamin d 25(oh) level and th1 and th2 pathway-derived cytokines in gd patients. methods: a prospective cohort study was conducted on 32 gd patients to compare the effect of sunlight exposure on vitamin d level and cytokines of th1 and th2 pathways between exposed and unexposed groups. exposed group received sunlight exposure three times a week for 30 minutes each between 9–11 a.m for 1 month. thyroid stimulating hormone (tsh), free thyroxin (ft4), vitamin d 25(oh), interferon-γ (ifn-γ) and interleukin-4 (il-4) serum levels, were investigated before and after one month of sunlight exposure. paired t-test or mann whitney test were used to analyze the difference between exposed and unexposed gd groups before and after sun exposure. results: one month of sunlight exposure increased vitamin d 25(oh) level by 27.90% among exposed gd group (15.34 ng/ml to 19.62 ng/ml, p<0.001). meanwhile, unexposed gd group’s vitamin d 25(oh) level decreased from 20.48 ng/ml to 18.86 ng/ml (p<0.001). increased vitamin d 25(oh) level in exposed group was not accompanied by the increase of il-4 level after sunlight exposure. conclusion: sunlight exposure increases vitamin d 25(oh) serum level and may affect the level of il-4, th2 pathwayderived cytokine, in patients with gd. however, the role of sunlight-derived vitamin d on ifn-γ in gd patients can not be concluded in this study.