Shift Work and Circadian Disruption

Sleep loss and health findings

A BMJ review drew on 38 meta-analyses and 24 systematic reviews. It found that the effect of shift work on sleep mainly concerns acute sleep loss around night shifts and early-morning shifts. It also reported links with accidents, type 2 diabetes (relative risk range 1.09 to 1.40), weight gain, coronary heart disease (relative risk 1.23), stroke (1.05) and cancer (1.01 to 1.32), although the original studies showed mixed results. [1] The authors say that the health and safety effects of shift work resemble those of insufficient sleep, and that more research is needed to know whether lost sleep is the causal pathway. [1] Label: mixed; relative risks are modest and come from observational data.

What "circadian disruption" means here

Shift work asks people to be awake and to sleep at times that run against the body clock. Whether the health links come from the clock mismatch, from lost sleep, or from both is not settled: the BMJ authors note the effects resemble those of insufficient sleep and that more research is needed. [1] A single person's risk cannot be read from these averages. For a longer research treatment see shift work and circadian misalignment research, and for chronotype see chronotype: what research shows.

What interventions have been tested

1. Bright light during night shifts

   insufficient evidence

   Two comparable studies (184 people) showed a small drop in sleepiness during the shift on one scale; evidence was very low quality. [2]

2. Naps

   insufficient evidence

   Results on reaction time and sleepiness were mostly not statistically significant; very low to low quality. [2]

3. Melatonin after a night shift

   promising but limited

   Low-quality evidence it may add about 24 minutes of daytime sleep versus placebo. [3]

4. Wake-promoting medicines (armodafinil, modafinil)

   promising but limited; a clinician's decision

   In people with shift work sleep disorder, they probably reduce sleepiness somewhat but adverse events were reported (headache, nausea, higher blood pressure). [3]

5. Caffeine plus pre-shift naps

   promising but limited

   One low-quality trial found less sleepiness. [3]

6. Hypnotic sleep medicines

   insufficient evidence

   One low-quality trial found no longer daytime sleep. [3]

The 2016 Cochrane review of non-drug approaches concluded it was not possible to determine whether bright light, naps or other interventions reduce sleepiness or improve sleep for shift workers, because the trials were few, varied and low in quality. [2] The 2014 review of drugs found no trials in shift workers without a sleep disorder. [3] Both reviews are several years old, and we did not check whether newer trials exist.

Wearables and shift work

Sleep trackers estimate sleep from movement and heart signals, and their accuracy is tested mostly in people sleeping at night. Proper evidence not found in the sources read for this page for how accurate consumer trackers are for daytime sleep after night shifts. See wearables vs sleep studies.

How to judge shift-work claims

• Does the claim cite a randomized trial in shift workers, or a lab study in students?
• Is a "circadian lighting" or supplement claim promising to "reverse" shift-work effects? Treat that as a marketing claim.
• Does it explain who was studied (nurses, drivers, factory workers)?