[Shift-work seniority increases the severity of sleep disorders. Comparison of different categories of shift-workers]

Shift-work disrupts the sleep-wake cycle and could bring about sleep disorders and excessive daytime sleepiness. We studied two samples of shift-workers, a group of 178 nurses and one of 174 police officers, all working in the town of Palermo (Italy); their answers to a sleep disorder questionnaire were scored and added in order to create a Sleep Disorder Score (SDS). The SDS cut-off value, discrimining pathological values from physiological ones, was settled a-priori. In both groups SDS did not depend on sex, age, weight, height nor on working seniority, but it increased non linearly (cubic form) with shift-work seniority. In nurses this mathematical description of SDS exceeded the cut-off value after 15 years of shift-work seniority; in police officers it settled asymptotically under the critical value. This could be ascribable both to the different composition in sex of the two samples (nurses: 49% F-51% M vs. police officers: 6% F-94% M) both to the self-selection process that seems to undergo police officers (nurses do not leave shift-work because of salary incentives).