Sleep and Substance Use Among Firefighters: Associations with Alcohol, Caffeine, and Nicotine Use

Purpose: Firefighters are at high risk for sleep disruption due to shift work. Use of alcohol, caffeine, and nicotine can also affect sleep. Thus, we evaluated daily, bidirectional associations between substance use and actigraphy-assessed sleep among firefighters. Patients and methods: Micro-longitudinal data were drawn from 120 firefighters participating in the Shiftwork in Firefighters (SWIFT) Study. Participants completed surveys on daily alcohol and caffeine use, current and lifetime tobacco use, and wore actigraphy devices to assess sleep timing, duration, and quality (2,617 observations). Multilevel models were used to examine both between- and within-person associations between substance use and subsequent sleep, and between sleep and next-day substance use. Models were adjusted for covariates (shift schedule, on-shift status, nighttime call volume, and naps). Results: Alcohol use demonstrated strong bidirectional associations with sleep. Greater within-person alcohol consumption predicted shorter sleep and earlier waketimes, while later sleep timing and shorter sleep predicted greater next-day alcohol use. Unexpectedly, greater caffeine consumption was associated with higher sleep efficiency and fewer nighttime awakenings at the between-person level and longer total sleep time at the within-person level. Current between-person use of smokeless tobacco was associated with approximately 30 minutes shorter total sleep time, whereas lifetime cigarette use showed no association with sleep outcomes. Conclusion: Substance use among firefighters exhibited substance-specific and temporally dynamic relationships with sleep. Nicotine and caffeine effects were largely person-dependent, whereas daily alcohol showed consistent bidirectional effects on sleep. These findings highlight potential intervention targets aimed at improving sleep and reducing alcohol-related risk among firefighters.