By Jim Spengler, MTI Contributor
There is an inextricable correlation between inadequate sleep and detrimental health outcomes. Fire service culture and wellness programs have done little to address the omnipresent problem of sleep deprivation. MTI publications describe the burden of constant fitness and individual responsibility towards one’s fitness. Understanding and taking steps to mitigate guaranteed sleep deprivation in a 24/7 public service is no different. It is part of a professional responsibility for the communities we serve and our crew.
In order to comprehend consequences fully, it is paramount to first understand our circadian cycles and the functions of sleep. Humans experience predictable internal patterns on an approximately 24 hour cycle. These patterns are influenced by an interplay of physiology, temperature and light/dark cycles. Physiologically, two compounds of note are adenosine and melatonin. The neurotransmitter adenosine builds-up during wakefulness. As adenosine builds, we get more sleepy. Importantly, adenosine will continue to build without sleep. Melatonin, a hormone released from the center of the brain, begins to rise soon after dusk. Melatonin regulates the timing of sleep, strengthened by cycles of sunrise and sunset. Additionally, melatonin helps to signal the rest of the body to begin the process of sleep. Once asleep, melatonin levels will ultimately fall to undetectable levels by sunrise. Similarly, sunrise and certain light wavelengths serve as an important regulatory function. Cycles of light exposure, such as sunrise, synchronize neural, hormonal, metabolic, and thermal networks within the body to external time. Lastly, predictable changes in body core temperature regulate alertness. Body temperature will rise through the afternoon, then fall as bedtime nears. The interplay between all four components regulate sleep at the most basic level (1, 2, 5). The function of sleep cannot be distilled into one domain. Broadly, sleep functions to consolidate memory, neural connections, and aid recovery during a complex, metabolically active, and deliberately ordered series of unique stages (1). The benefits of sleep are widespread and well-evidenced. Obtaining quality, consistent sleep is unarguably a cornerstone to a healthy existence. Of particular benefit to tactical athletes, adequate sleep benefits performance, recovery, and decision making (7).
The consequences of sleep deprivation and circadian disruption are well documented and too long to list. Acutely, effects include diminished reaction time, decreased vigilance, and decreased power output. One night of sleep disruption can lead to changes in mood, blood sugar regulation and gastric upset. Chronic effects include increased risk of certain cancers, diabetes, obesity, cardiovascular disease, and neurodegenerative disorders (1, 4). A night of sleep deprivation could intuitively lead to implementation of “catching-up” the following day. However, a 2021 study shows that the build up of molecular waste from missed sleep opportunities does not improve once subjects were allowed normal sleep patterns the following 48 hours (14). Once done, sleep loss cannot be “undone”.
The crux of the problem lies at the intersection of sleep’s benefits and the 24-hour operational environment tactical athletes face. The fire service is not unique to the consequences of sleep deprivation. Civilians who enlist in the military must rapidly transition into an organization where restricted and intermittent sleep is normal. In a 2020 review, The US Army Research Lab notes the sleep challenges soldiers face from continuous operations. The most notable barriers discussed were sleeping environment, noise, jet lag, shift work and deployment stressors. The authors also described soldier’s perception of inadequate sleep, alcohol and stimulant use, altitude insomnia, and other general medical disorders as contributors to sleep disruption (6). Twenty-four hour operational tempos are a necessity to mission success. Nevertheless, it is paramount to acknowledge that execution of physically and cognitively demanding tasks will be impaired by the inability to acquire adequate sleep. US Army research also found that for every hour of sleep lost, combat effectiveness decreased 15 to 25 percent. Further, the risks of sleep deprivation and contribution to mishaps specific to aviation were acknowledged decades ago (13). More recently, the emergence of long-haul flights which change multiple timezones elicited federal rule changes enforcing flight time limitations and rest requirements.
Modern firefighting shift work schedules all but guarantee sleep interruptions and circadian disruption. The normal interplay between external lighting cues and internal physiology patterns becomes erratic after the 3am call. For example, detrimental effects can stem from bright lights in a patient’s home or hospital (3). This bright light exposure effectively creates jet-lag, shifting our body’s perceived time zone and blunting melatonin production. Interestingly, melatonin is the only known anti-cancer, circadian driven signal in human and animal models. Studies of shift workers exposed to nighttime light, showed increased incidence of breast cancer and resistance of the cancer to interventions. This evidence was compelling enough for the International Agency for Research on Cancer, a branch of the World Health Organization, to state that shift work involving circadian disruption is probably carcinogenic to humans. Other sleep disruptors experienced on-shift could include temperature fluctuations, noise and nervous system activation. For example, in response to night tones, heart rate increases 20 beats per minute on average to as high as 60 bpm. Cortisol, a stress hormone, remains higher 30 minutes to 120 minutes post-alarm at night compared to daytime controls. This increased arousal state defeats our ability to fall back asleep. Lastly, body temperature as a result of the sleeping environment or physical activity alters sleep (17). Once researchers peripherally warmed sleeping subjects, wakefulness increased and sleep quality decreased similar to levels observed in clinical insomnia. Any of the above can combine during a medical call, auto-accident or structure fire to acutely and chronically disrupt sleep and circadian cycles.
The dangers of sleep deprivation aside, there are several proven mitigation practices to manage and offset the consequences. The following is not an all-inclusive list, but has anecdotally proven beneficial for me. Current research also supports these practices.
- Yoga nidra (10): Yoga Nidra, also recently named Non-Sleep Deep Rest, is a script-based relaxation practice done seated or lying down. Studies have shown that Yoga Nidra sessions can lead to lower stress, higher perceived well-being, and improved sleep quality. This is most likely due to Yoga Nidra’s ability to counter hyper-arousal responses, such as cortisol increases. For several months, I have developed the habit of completing 10-20 minute Yoga Nidra sessions after shifts of sleep deprivation. This practice can also be used to assist in falling asleep. I have subjectively felt better after these sessions and found I can fall asleep easier the following night. Yoga Nidra or NSDR can be found for free on YouTube.
- Short naps (9): Napping for 20-90 minutes has been shown to be preventive in anticipation of lost sleep. As previously stated, once a debt is incurred it cannot be bought back. However, “banking up” sleep during the day has proven effective on performance and alertness during deprivation conditions that night. Fire service culture stigmatizes napping on-duty in some cases. A balance needs to be struck between technical/training proficiency and health. A 20 minute nap in the afternoon during a 24 hour shift can be highly beneficial while not compromising training opportunities. In addition, nap lengths of longer than 90 minutes (one sleep cycle) have been shown to cause an increased perception of fatigue. This fatigue, called sleep inertia, is most notably felt upon awakening. This grogginess, that dissipates with time, is associated with significant cognitive performance deficits (15). For these reasons, napping on duty should be kept short. Napping off-duty is a balance. While “making-up” for sleep is a misnomer, naps post-sleep deprivation conditions are strongly supportive of physical and cognitive performance, decreased fatigue and improved psychological state. It is important to note that longer naps (>90 minutes) and naps later in the day (4-8p) may interfere with sleep that night. This is due to not enough adenosine accumulating to induce sleepiness. Subjectively, I have had good success with napping mid-morning or early afternoon.
- Meal timing (8, 11): Research has shown that meal timing, eating at similar times day to day, helps to set the circadian system, especially in cases of shift work. My meal timing rarely deviates on-duty to off-duty, staying approximately within a nine to ten hour window. My energy levels and sleep seem to have benefited.
- Light exposure (2, 19): Exposing my eyes to morning sunlight seems to have been one of the most important overall changes I have made this year. The benefits physiologically are well-evidenced. Early morning light helps serve as a signal to the body’s internal clock. This signal ensures consistent melatonin production and has been shown to boost the ability to fall asleep. Early morning light also has been shown to improve mood and immunity. My well-being and sleep habits have been much more consistent. At minimum, I strive for 10-15 minutes outside in the morning around sunrise. I also try to avoid bright artificial light prior to sleep and sleep in a blacked-out room. This is difficult on-shift depending on station design and call volume.
- Consistent regular fitness training time (1, 12, 18): Similar to meal-timing, training at consistent times every day helps to anchor the circadian rhythm. I train in the morning whenever possible. Personally, if I train anywhere between 5-7p, I’m unable to fall asleep by my preferred time of 9p.
- Temperature of sleeping environment (1, 12): To fall/stay asleep, we need to experience a drop in body temperature. I’ve invested in a cooling mattress “topper” for use at home. At the firehouse, the best I can do is set my bunk room temperature to 65-70 degrees, the lower the better.
- Mindful caffeine intake (16): I take great pleasure in a morning cup of coffee. However, caffeine acts as an adenosine receptor antagonist. In other words, it will make you feel awake-but impairs the ability for adenosine to be “cleared” from your system. This helps to explain the cycle of alertness and grogginess some feel over the course of a shift with chronic caffeine consumption. Reductions in adenosine are blunted by reaching for the coffee pot over and over. I have adopted the habit of waiting 60-90 minutes to drink my coffee in the morning, letting my body wake up on its own. Similarly, I avoid caffeine late in the day to allow the buildup of sleep pressure via adenosine. Personally, I found that any caffeine ingested after 3p affects my sleep. However, there are varying levels of individual tolerance (16).
The fire service faces numerous dangers to health and performance that most outsiders could identify. Products of combustion cause cancer. The steady stream of traumatic experiences causes mental health crises. The more insidious danger is the 3am tones, shift after shift for years. If our organizations do not have the will or means to implement actionable changes, one should take all individual steps they can to ensure enduring fitness and longevity.
Jim Spengler is a career firefighter for a department in the DC metropolitan area. Jim completed a M.S. in Exercise Science in 2013.
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- Why we sleep: Unlocking the power of sleep and dreams. Matthew Walker, 2017.
- Recommendations for daytime, evening, night time light exposure to best support physiology, sleep, and wakefulness in healthy adults. PLOS Biology. Brown, et al, 2022.
- Evening home light adversely impacts circadian rhythm and sleep. Nature. Cain, et al, 2020.
- Circadian Disruption and Human Health: A bidirectional relationship. Eur J Neuro. Abbott, et al, 2018.
- Health consequences of electric lighting practices in the modern world: A report on the National Toxicology Program’s Workshop on shift work at night, artificial light at night, and circadian disruption. Sci Total Environ. Lunn, et al, 2017.
- Sleep in the US Military. Nature. Cameron, et al, 2019.
- The effects of sleep on firefighter occupational performance and health: A systematic review and call to action. Sleep Epidemiology Frost, et al, 2021.
- Meal timing regulates the human circadian system. Current Biology. Wehrens, et al, 2017.
- To nap or not to nap? A systematic review evaluating napping behavior in athletes and the impact on various measures of athletic performance. Nature and Science of Sleep. Lastella, et al, 2021.
- Effectiveness of a short Yoga Nidra meditation on stress, sleep, and well-being in a large and diverse sample. Current Psychology. Moszeik, et al, 2020.
- Protocol for a randomized controlled trial on the feasibility and effects of 10-hour time-restricted eating on cardiometabolic disease risk among career firefighters doing 24-hour shift work: the Healthy Heroes Study. Cell Metabolism. Manoogian, et al, 2021.
- The effects of ventilation and temperature on sleep quality and next day work performance: pilot measurements in a climate chamber. Building and Environment. Fan, et al, 2021.
- Fatigue in aviation: Safety risks, preventive strategies, and pharmacological interventions. Frontiers in Physiology. Wingelaar-Jagt, et al, 2021.
- Sleep deprivation impairs molecular clearance from the human brain. Brain. Eide, et al, 2021.
- Sleep inertia: current insights. Hilditch, et al, 2019.
- Adenosine, caffeine, and sleep-wake regulation: state of the science and perspectives. Journal of Sleep Research. Reichert, et al, 2022.
- Sleeping with an electric blanket: effects on core temperature, sleep and melatonin in young adults. Sleep. Fletcher, et al, 1999.
- The circadian typology: The role of physical activity and melatonin. Sport Sciences for Health. Montaruli, et al, 2017.
- Benefits of Sunlight: A bright spot for humans. Environmental Health Perspectives. Mead, 2008.