Sleep hygiene - What do we mean? A bibliographic review.

There is no consensus on the definition of sleep hygiene and its components. We examined the definition of sleep hygiene based on its use in published studies. Four databases (Medline, EMBASE, PsycINFO and CINAHL) were searched from inception until December 31, 2021 for the phrase 'sleep hygiene' in the title or abstract. We identified 548 relevant studies in adults: 250 observational and 298 intervention studies. A definition of sleep hygiene was provided in only 44% of studies and converged on three themes: behavioural factors, environmental factors, and an aspect of control. Sleep hygiene components were explicitly defined in up to 70% of observational studies, but in only 35% of intervention studies. The most commonly considered components of sleep hygiene were caffeine (in 51% of studies), alcohol (46%), exercise (46%), sleep timing (45%), light (42%), napping (39%), smoking (38%), noise (37%), temperature (34%), wind-down routine (33%), stress (32%), and stimulus control (32%), although the specific details of each component varied. Lack of consistency in definitions of sleep hygiene and its components may hinder communication between researchers, clinicians, and the public, and likely limits the utility of sleep hygiene as an intervention.

Temporal and bidirectional associations between physical activity and sleep in primary school-aged children.

The directionality of the relationship between children's physical activity and sleep is unclear. This study examined the temporal and bidirectional associations between objectively measured physical activity, energy expenditure, and sleep in primary school-aged children. A subgroup of children (n = 65, aged 8-11 years) from the Fitness, Activity and Skills Testing Study conducted in Melbourne, Australia, had their sleep and physical activity assessed using the SenseWear Pro Armband for 8 consecutive days. Outcome measures included time spent in light-intensity physical activiy (LPA), moderate- to vigorous-intensity physical activity (MVPA), activity energy expenditure (AEE), time in bed, total sleep time, and sleep efficiency. Multilevel analyses were conducted using generalized linear latent mixed models to determine whether physical activity on 1 day was associated with sleep outcomes that night, and whether sleep during 1 night was associated with physical activity the following day. No significant associations were observed between time in bed, total sleep time, and sleep efficiency with LPA, MVPA, and AEE in either direction. This study found no temporal or bidirectional associations between objectively measured physical activity, AEE, and sleep. Future research is needed to understand other sleep dimensions that may impact on or be influenced by physical activity to provide potential intervention targets to improve these outcomes.

The Impact of Sleep Restriction and Simulated Physical Firefighting Work on Acute Inflammatory Stress Responses.

OBJECTIVES: This study investigated the effect restricted sleep has on wildland firefighters' acute cytokine levels during 3 days and 2 nights of simulated physical wildfire suppression work. METHODS: Firefighters completed multiple days of physical firefighting work separated by either an 8-h (Control condition; n = 18) or 4-h (Sleep restriction condition; n = 17) sleep opportunity each night. Blood samples were collected 4 times a day (i.e., 06:15, 11:30, 18:15, 21:30) from which plasma cytokine levels (IL-6, IL-8, IL-1ß, TNF-α, IL-4, IL-10) were measured. RESULTS: The primary findings for cytokine levels revealed a fixed effect for condition that showed higher IL-8 levels among firefighters who received an 8-h sleep each night. An interaction effect demonstrated differing increases in IL-6 over successive days of work for the SR and CON conditions. Fixed effects for time indicated that IL-6 and IL-4 levels increased, while IL-1ß, TNF-α and IL-8 levels decreased. There were no significant effects for IL-10 observed. CONCLUSION: Findings demonstrate increased IL-8 levels among firefighters who received an 8-h sleep when compared to those who had a restricted 4-h sleep. Firefighters' IL-6 levels increased in both conditions which may indicate that a 4-h sleep restriction duration and/or period (i.e., 2 nights) was not a significant enough stressor to affect this cytokine. Considering the immunomodulatory properties of IL-6 and IL-4 that inhibit pro-inflammatory cytokines, the rise in IL-6 and IL-4, independent of increases in IL-1ß and TNF-α, could indicate a non-damaging response to the stress of simulated physical firefighting work. However, given the link between chronically elevated cytokine levels and several diseases, further research is needed to determine if firefighters' IL-8 and IL-6 levels are elevated following repeated firefighting deployments across a fire season and over multiple fire seasons.