Aims and background: Melatonin secretion is required to be a potential inhibitor of the development and growth of tumors, and cigarette smoking is a well established risk factor for cancer at various sites.
Methods: Circulating melatonin levels of 20 smokers and 20 non smokers (controls), sampled at the same hour from awaking in order to obtain a comparable circadian synchronization, were compared.
Results: Our data showed higher melatonin circulating levels in smokers (17.44 +/- 1.8 pg/ml) than in nonsmokers (9.77 +/- 1.4 pg/ml).
Conclusions: The causes, mechanism and meaning of this phenomenon are still unknown. The most attractive hypothesis considers higher melatonin levels in smokers as an attempt to counterbalance cellular growth stimulus, a natural "brake" mechanism to restrain the proliferation of normally differentiated tissues: smoke is a prominent risk factor for several different tumors.