Smoking and combined oral contraceptives should be considered as an independent variable in sex and gender-oriented studies

The influence of sex combined with smoking and combined oral contraceptives (COC) use on atherogenic indexes is scarcely studied. Thus, traditional lipid parameters were measured, and non-traditional atherogenic indexes were calculated in a young and healthy population of men, COC-free women, and COC users. Total cholesterol (TChol), low-density lipoprotein (LDL), high-density lipoprotein (HDL), and HDL/LDL ratio were lower in men, while triglycerides (TG)/HDL ratio, atherogenic index of plasma (AIP), Castelli's Risk Index I (CRII) and CRI-II, atherogenic coefficient (AC), creatinine, creatinine clearance, and estimated glomerular filtration rate (eGFR) were higher in men. The use of COC modified TChol, HDL, TG, TG/HDL, and AIP which had significantly higher values in COC users. In addition, TG were also increased in COC users in comparison with men. Smoking reduced sexually divergent parameters: BMI, TG, HDL/LDL, TG/HDL, AIP, CRII, CRI-II, and AC became similar among the three cohorts, losing the reported sex differences. Smoking also reduced differences in TChol, HDL, TG, and AIP between COC-free women and COC users, but it does not affect CRII, CRI-II, creatinine, creatinine clearance, and eGFR, underlining that COC users and COC-free women have to be considered two different populations. Our results represent a complex landscape suggesting that for both sexes smoking should be an independent variable in medical studies. Moreover, in women, the use of COC evidenced two different cohorts. Thus, more variables should be considered during a single study indicating that sex, smoking, and COC should be studied together to get a picture of the real-life context.