INS and metabolic syndrome: Among the participants without proliferation, an elevated monocyte level was significantly associated with a decreased prevalence of DR in both the initial model adjusting for age, sex and duration of diabetes and in the full model adjusting for age, sex, education status, duration of diabetes, current smoking, BMI, HbA1c, dyslipidemia, systolic blood pressure and insulin therapy (Additional file 1: Table S1).