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Circadian Sleep Propensity and Alcohol Interaction at the Wheel.

STUDY OBJECTIVES
The study was aimed at estimating the effect of alcohol consumption, time of day, and their interaction on traffic crashes in a real regional context.


METHODS
Blood alcohol concentration (BAC) data were collected from drivers involved in traffic accidents during one year in an Italian region and in a control group of drivers over the same road network. Mean circadian sleep propensity was estimated from a previous study as function of time of day. Accident risk was analyzed by logistic regression as function of BAC and circadian sleep propensity.


RESULTS
BAC values greater than zero were found in 72.0% of the drivers involved in crashes and in 40.4% of the controls. Among the former 23.6% of the drivers exceeded the BAC legal threshold of 0.05 g/dL, while illegal values were found in 10.4% of the controls. The relative risk showed a significant increase with both BAC and circadian sleep propensity (as estimated from time of day) and their interaction was significant.


CONCLUSIONS
Due to the significant interaction, even low BAC levels strongly increased accident risk when associated with high sleep propensity.