Of the 77 assayed CpG sites in the promoter regions of the five circadian genes, methylation variation at 6 CpG sites (3 in CLOCK, 2 in BMAL1, 1 in PER2) was significantly associated with insulin resistance, methylation at 8 CpG sites (4 in CLOCK, 2 in BMAL1, 2 in PER2) was associated with fasting glucose, and methylation at 3 CpG sites (2 in BMAL1, 1 in PER2) was associated with HbA1c (all P < 0.05), after correction for covariates. The gene discussed is CLOCK; the disease is Insulin resistance.