GC and chronic obstructive pulmonary disease: Therefore, assuming a linear logistic relationship between circulating 25OHD concentrations and the risk of COPD, an inverse association (WMD: −2.07, 95% CI: −3.72 to −0.41, p = 0.015) was noted after using VDBP gene rs7041 polymorphism as an instrument for Mendelian randomization analyses.