Vitamin D deficiency and high serum IL-6 concentration as risk factors for tubal factor infertility in Chinese women

OBJECTIVES: The aim of this study was to investigate the relationship between 25-hydroxyvitamin-D [25(OH)D] and female infertility and to further explore the role of inflammatory cytokines. METHOD: We recruited 356 infertile women diagnosed with tubal factor infertility (TFI) or polycystic ovary syndrome (PCOS) or endometriosis, as well as 180 fertile women. Serum concentrations of 25(OH)D, interleukin (IL)-6, IL-1 β, and interferon-α were measured. RESULTS: The 25(OH)D concentration in TFI women was the lowest (16.9 ng/mL) and was significantly different from that in the fertile women (19.4 ng/mL; P <0.05)]; whereas women with TFI had higher IL-6 concentrations. After adjusting for confounders, 25(OH)D deficiency presented a risk factor for TFI (odds ratio [OR], 4.2; 95% confidence interval [CI], 1.5-11.3). There was a dose-effect relation between IL-6 tertiles and TFI: the higher the IL-6, the higher the risk for TFI (middle versus low: OR, 3.7; 95% CI, 1.5-9.5; high versus low: OR, 13.2; 95% CI, 4.8-36.4). IL-6 showed a negative correlation with 25(OH)D (r = -0.19). Women with both high IL-6 and low 25(OH)D had the highest risk for TFI (OR, 10.6; 95% CI, 4.2-26.3). CONCLUSIONS: Both vitamin D deficiency and high serum IL-6 concentration are risk factors for TFI. Serum 25(OH)D concentration was significantly and negatively correlated with serum IL-6. There was an interaction between IL-6 and 25(OH)D for the risk for TFI-related infertility. We hypothesized that vitamin D might reduce the risk for TFI through suppressing the production of IL-6.