Inclusion criteria:
Underground employees who use artificial light only during the period of their presence
No specific disease or chronic physical and mental illness
Male
Have at least 21 and a maximum of 30 years
Exclusion criteria:
Taking medications that could affect serum melatonin levels including
Having depression or any other major psychiatric disorders on DSM IV
Having significant acute or chronic systemic disorders including type I diabetes mellitus, uncontrolled thyroid disorders, kidney/prostate/bladder problems which cause excessive urination, congestive heart failure, angina pectoris or other major cardiovascular disorders, hepatitis, asthma or severe respiratory allergies, stroke, Parkinson’s disease, Alzheimer’s disease, schizophrenia, epilepsy, oncologic disorders if less than 1 year since end of treatment, or chronic infections
Use of hypnotics, melatonin, stimulants, or other medications that may affect melatonin levels (e.g. β blockers, drugs that affect prostaglandin synthesis, or drugs that activate hepatic melatonin metabolism) and unwillingness or inability to discontinue the occasional use of these medications for at least 4 weeks before beginning of the study