INS and type 2 diabetes mellitus: By analyzing skeletal muscle biopsy samples from smokers and non-smokers, Bergman et al. found that smokers had increased Ser636 phosphorylation of IRS-1 and reduced PPAR-γ expression, resulting in reduced insulin sensitivity (Caligiuri and Kenny, 2021), which is consistent with the conclusion that nicotine aggravates insulin resistance in patients with type 2 diabetes and healthy smokers (Chen et al., 2023).