Cigarette smoking has a positive and independent effect on testosterone levels.

Previous studies have suggested that testosterone levels are linked to a variety of diseases, such as cardiovascular disease, type-2 diabetes, the metabolic syndrome, erectile dysfunction, depression, stroke and osteoporosis. Since cigarette smoking is a major health problem and highly prevalent among men, several groups have studied the effects of cigarette smoking on testosterone levels in men. However, the results have been conflicting. Our objectives were to examine the association of cigarette smoking and serum levels of sex hormone-binding globulin (SHBG), total testosterone (TT) and free testosterone (FT) in a large male population. Data from 2,021 men (989 nonsmokers and 1,032 smokers), aged 20-69, were collected from the Fangchenggang Area Male Health and Examination survey using an in-person interview and self-administered questionnaires from September to December, 2009. We have found the following: (a) smokers had significantly higher TT and FT levels compared to nonsmokers, even after stratification as per age, BMI, triglycerides and alcohol consumption. (b) Both TT (r = -0.083, P <0.001) and FT (r = -0.271, P <0.001) levels were negatively correlated to the amount of tobacco exposure. (c) Smoking was an independent influencing factor for the levels of both TT (unadjusted OR = 1.64, 95% CI: 1.33-2.01, P <0.001; adjusted OR = 1.69, 95% CI: 1.34-2.13, P <0.001) and FT (unadjusted OR = 1.32, 95% CI: 1.08-1.61, P = 0.007; adjusted OR = 1.27, 95% CI: 1-1.61, P = 0.050) levels in multivariate logistic regression models before and after adjusting for age, BMI, fasting blood glucose, triglycerides, alcohol consumption and estradiol. (d) Smoking was not found to be an independent predictor of SHBG level after adjustment for confounders in multivariate regression model (P >0.05), although a positive association between increasing pack-years and SHBG level was observed (r = 0.174, P <0.001). More research is needed to elucidate the biological mechanisms and clinical significance of these associations.