GSTM1 and polycythemia: Ge et al. found that heavy smokers (20 cigarettes per day for 15 years) had lower mean forced expiratory flow during the middle half of the forced vital capacity (FEF25–75%) and SaO2 levels, while higher Hb levels than non-smokers, suggesting that smoking may induce excessive polycythemia due to increased carboxyhemoglobin and hypoxemia.59 The prevalence of polycythemia among smokers was approximately 3 times higher compared to non-smokers.59 Interestingly, CMS patients with cobalt toxicity exhibited greater polycythemia, indicating the contribution of cobalt to CMS progression.60