A colleague of mine retired last year at age 58. Healthy by standard measures, still intellectually sharp, and still enjoying the work, he left because he was tired — but in a way that sleep no longer fixed. After 26 years of emergency medicine, 15 of them working primarily nights, he did not burn out dramatically. He just ran out of reserve.
I have been thinking about that distinction ever since. There is a body of literature on sleep optimization for shift workers, and it is useful as far as it goes. But I think sleep is downstream of a more fundamental problem. The question that is not asked often enough is not how to sleep better after a night shift, but how to preserve enough physiologic reserve across a career to still deliver the same quality of care at year 25 as at year 5.

Those are genuinely different questions, with different answers.

Name the Exposure First

We accept occupational hazard framing in other contexts without much argument. Lead aprons during fluoroscopy. Hepatitis B vaccination. Hearing protection on the flight line. In each case, the exposure is identified, the risk is characterized, and the mitigation is protocolized. We do not tell flight crew to simply be more careful around the engines.
Night shift work warrants the same framework. A 2021 dose-response meta-analysis found that shift work carried 35 percent higher pooled odds of metabolic syndrome, and a 2018 meta-analysis of 21 studies found a 17 percent higher risk of any cardiovascular disease event and a 26 percent higher risk of coronary heart disease morbidity.1,2 The International Agency for Research on Cancer classifies night shift work as probably carcinogenic to humans (Group 2A).3 Group 2A is a hazard classification, not a risk estimate at any particular level of exposure. A 2024 cross-sectional study of 45 female night-shift nurses and 44 female daytime workers reported higher electroencephalogram-derived brain age index values and less N3 sleep among the night-shift group; the authors interpreted the findings as consistent with accelerated brain aging while calling for longitudinal confirmation.4 These are occupational health data. They belong in the same category as radiation exposure and bloodborne pathogen risk, not in a wellness column.

Sleep optimization is a reasonable first step. Yet it is not an adequate response to that body of evidence.

The Case for Cardiorespiratory Fitness

Cardiorespiratory fitness is among the strongest and most consistent predictors of long-term health outcomes in the literature. A 2009 JAMA meta-analysis of 33 cohort studies found that each 1-MET higher maximal aerobic capacity was associated with a 13 percent lower risk of all-cause mortality and a 15 percent lower risk of coronary heart disease/cardiovascular disease events.5 For physicians already carrying elevated baseline risk from years of circadian disruption, building and maintaining aerobic capacity is not an optional add-on to the mitigation strategy. It may be a central element of it.

The clinical analogy is worth taking seriously. When we talk about physiologic reserve in patients, we mean the capacity to tolerate a major stressor without decompensating. The fit patient survives the major abdominal surgery that would kill the deconditioned one, not because the surgery was different but because the human being was different. Night shift work is a chronic stressor. It does not arrive as a single acute event that kills you; it degrades the baseline, year by year, until the reserve is no longer there when something else demands it. My colleague at age 58 had not had a cardiac event; he had just spent 15 years on night shifts without rebuilding what nights were taking out of his body.

The scheduling challenge is real. Ten or more night shifts a month can make it hard to consistently meet standard exercise targets: at least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity aerobic activity per week.6 The answer need not be a conventional long-duration program. A meta-analysis of 53 randomized trials found that high-intensity interval training improved VO2max across populations; even short-interval, low-volume protocols were effective compared with no-exercise controls.⁷ Steady moderate-intensity (“Zone 2”) aerobic work is a complementary option. These approaches can be distributed around shift blocks rather than performed on consecutive days.

Muscle Mass Is Not Optional in Midcareer

In healthy young men, five nights of sleep restriction lowered myofibrillar protein synthesis — though performing high-intensity interval exercise during that same period held synthesis at control levels.8 In a separate controlled protocol, circadian misalignment reduced skeletal-muscle insulin sensitivity and shifted fatty-acid metabolism gene profiles.9 These mechanisms may contribute to metabolic risk before it becomes obvious on a scale or in a routine metabolic panel. Emergency physicians who are not actively maintaining muscle through resistance training may be accumulating that risk in the background, regardless of how they look outside or feel inside.

Two to three resistance-training sessions a week, fitted around shift schedules, are consistent with American College of Sports Medicine guidance for healthy adults and provide a practical floor for maintaining muscle and strength.6 Muscle is metabolically active tissue; maintaining it as we age is not a fitness preference, it is a clinical decision with real long-term consequences. We counsel patients on this regularly, in the context of diabetes management, cardiovascular risk reduction, and healthy aging. Biology does not change because the patient is also the physician.

Recovery Has to Be Scheduled

Emergency physicians are reliably disciplined about one thing: showing up. Recovery gets whatever is left over, which on a busy rotation is often not much. The problem with that approach is that recovery is not simply the absence of work. It is a physiologic process that, when it gets consistently shorted, compounds the occupational exposure rather than counteracts it.

Previous ACEP Now articles have handled sleep architecture for shift workers and shift work sleep disorder well, and I will not retread that ground. Beyond sleep, recovery for the night-shift physician also means nutrition timing that does not fight the metabolic clock during the biological night; enough unstructured time between shift blocks for the autonomic nervous system to actually down-regulate; and managing family and social obligations around the schedule with some deliberateness, rather than treating them as infinitely compressible. None of this requires a wearable device or a supplement stack. It requires treating recovery as a scheduled commitment rather than a default state.

Toughness Is Not the Same as Mitigation

Emergency physicians might recognize this response: “I can handle it!” We usually can, and have, for a long time. But our ability to tolerate the problem makes it invisible right up until it is no longer tolerable.

Night-shift work carries a well-characterized set of long-term risks. Countermeasures are not complicated: cardiorespiratory fitness, muscle maintenance, and recovery as a clinical priority rather than a leftover experience. Physicians who manage this actively over a long career do not escape the exposure, but they arrive at year 25 in a meaningfully different physiologic position than those who simply absorbed it.

We spend careers fighting against this exact kind of accumulated chronic disease in the people who come through the doors of our emergency departments. We must apply that same attention to ourselves. My colleague had good habits. He was not careless. He just never thought of nights as something that required active mitigation. He thought of it as the job and that he was tough enough to get through it. For 26 years, he was right. That is the thing about reserve: you do not notice it going, and you cannot borrow it back once it is gone. The distinction between toughness and active management is the one I wish someone had made explicit to him earlier. Thus, I’m making it explicit to you now.

Dr. Shermer is a professor of emergency medicine at the University of Mississippi Medical Center, medical director for AirCare HEMS, Critical Care Ground Transport, and the TelEmergency telemedicine network, and state surgeon for the Mississippi Army National Guard. He is the founder of Global MedOps Command and the author of Night Shift Strong (Global MedOps Command, 2026).

References

1. Wang Y, Yu L, Gao Y, et al. Association between shift work or long working hours with metabolic syndrome: a systematic review and dose-response meta-analysis of observational studies. Chronobiol Int. 2021;38(3):318-333. doi:10.1080/07420528.2020.1797763
2. Torquati L, Mielke GI, Brown WJ, Kolbe-Alexander T. Shift work and the risk of cardiovascular disease: a systematic review and meta-analysis including dose-response relationship. Scand J Work Environ Health. 2018;44(3):229-238. doi:10.5271/sjweh.3700
3. IARC Working Group on the Identification of Carcinogenic Hazards to Humans. Night Shift Work. IARC Monographs on the Identification of Carcinogenic Hazards to Humans, Volume 124. Lyon, France: International Agency for Research on Cancer; 2020.
4. Yook S, Choi SJ, Lee H, Joo EY, Kim H. Long-term night-shift work is associated with accelerates [sic] brain aging and worsens N3 sleep in female nurses. Sleep Med. 2024;121:69-76. doi:10.1016/j.sleep.2024.06.013
5. Kodama S, Saito K, Tanaka S, et al. Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis. JAMA. 2009;301(19):2024-2035. doi:10.1001/jama.2009.681
6. Garber CE, Blissmer B, Deschenes MR, et al; American College of Sports Medicine. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Med Sci Sports Exerc. 2011;43(7):1334-1359. doi:10.1249/MSS.0b013e318213fefb
7. Wen D, Utesch T, Wu J, et al. Effects of different protocols of high intensity interval training for VO2max improvements in adults: a meta-analysis of randomised controlled trials. J Sci Med Sport. 2019;22(8):941-947. doi:10.1016/j.jsams.2019.01.013
8. Saner NJ, Lee MJC, Pitchford NW, et al. The effect of sleep restriction, with or without high-intensity interval exercise, on myofibrillar protein synthesis in healthy young men. J Physiol. 2020;598(8):1523-1536. doi:10.1113/JP278828
9. Wefers J, van Moorsel D, Hansen J, et al. Circadian misalignment induces fatty acid metabolism gene profiles and compromises insulin sensitivity in human skeletal muscle. Proc Natl Acad Sci USA. 2018;115(30):7789-7794. doi:10.1073/pnas.1722295115