How much does shift work raise the risk of heart disease?
The strongest-graded health finding in shift-work research, and why cumulative years on nights matter more to your roster than the single headline risk figure.
Reviewed against primary sources on July 19, 2026 by the Soon operations research team
The evidence in one line
Shift work is associated with a higher rate of myocardial infarction at a relative risk of 1.23 (95% CI 1.15-1.31), the finding an umbrella review (Wu et al., 2022) graded highly suggestive, the top tier this field reaches. For a scheduler, the more useful number is the dose-response: each additional 5 years of night-shift exposure is associated with a further RR 1.07 for cardiovascular incidence (Xi et al., 2025). All of it is observational, so read this as a strong association, not proven cause.
The strongest-graded finding in shift-work health research
Of everything studied about shift work and the body, cardiovascular disease carries the strongest evidence. An umbrella review (Wu et al., 2022) graded the association between shift work and myocardial infarction at a relative risk of 1.23 (95% CI 1.15-1.31) as highly suggestive, the top tier this field reaches. That estimate traces to the landmark Vyas et al. 2012 BMJ meta-analysis, which pooled 34 studies covering 2,011,935 people.
A more recent dose-response meta-analysis (Xi et al., 2025) adds the broader endpoint. Across 23 cohort studies and 3.34M participants, night-shift work is associated with total cardiovascular events at a relative risk of 1.13 (95% CI 1.10-1.16). Both numbers describe a group-level pattern: night and shift workers show higher rates of these events than comparable day workers, which is not a certainty for any one person.
Why the per-5-year number matters more on a roster
The headline relative risks answer a binary question, whether a role involves night work or not. A scheduler cannot change that a hospital, a plant, or a control room needs someone awake overnight. What a roster does control is how many years of that exposure any single person accumulates, and this is exactly what the dose-response describes.
Xi et al. (2025) found that each additional 5 years of night-shift exposure is associated with a further relative risk of 1.07 for cardiovascular incidence and 1.05 for cardiovascular mortality. Read operationally, that reframes night work from a fixed label into a metered quantity. A worker's lifetime night dose is the running sum of scheduling decisions made across their career, so the risk gradient tracks a variable a roster actually sets.
This is why concentrating night coverage on a small, permanent core is the pattern most worth questioning. Spreading the same total night hours across more people keeps any individual's cumulative exposure lower, which targets the one factor the association scales with. The point is not that anyone should stop staffing nights, it is that lifetime dose is a lever and the binary headline hides it.
Reading the caveat without flinching
Every input here is observational. Xi et al. self-rate their GRADE certainty as low to very low, and no randomized trial assigns people to decades of night work, so none ever will. That means this is a strong association, not proven causation, and the honest word for the evidence stays associational.
It also means highly suggestive is as high as this field climbs, and it was reached across more than two million people in Vyas and 3.34M participants in Xi. Consistency at that scale is what strong looks like when a controlled experiment is impossible. Absence of trial-grade proof is not evidence of safety, and it should not be read as reassurance.
What this means for your schedule
- Record cumulative years on nights for each worker, not only the current rota, because the cardiovascular association scales per 5-year block.
- Rotate long-tenured staff off standing night lines before they build up long uninterrupted exposure histories.
- Distribute required night coverage across a wider pool so no single person carries a decades-long night dose.
- Set an explicit ceiling on lifetime night tenure and review it the way you review any other exposure limit.
- Treat night staffing as a dose you meter over a career, since the RR 1.07 per 5 years is the variable a roster can actually move.
The business case
Cardiovascular disease is the strongest-graded health signal in shift-work research, with myocardial infarction associated at RR 1.23 and rated highly suggestive, so it is the exposure most likely to surface in occupational-health claims, insurer scrutiny, and duty-of-care expectations.
Because the risk is associated with cumulative years rather than any single shift, the organizations most exposed are those that concentrate decades of night work on a small, long-tenured core.
Spreading night exposure across a larger pool is a governance decision as much as a scheduling one, and it is the response that maps to how the evidence behaves.
Frequently asked questions
- How much does shift work raise heart-attack risk?
- Shift work is associated with myocardial infarction at a relative risk of 1.23 (95% CI 1.15-1.31), a finding an umbrella review (Wu et al., 2022) graded highly suggestive. The estimate traces to the Vyas et al. 2012 BMJ meta-analysis of 34 studies and 2,011,935 people. It is an association across large populations, not a prediction for one individual.
- What does the per-5-year dose-response actually mean?
- A dose-response meta-analysis (Xi et al., 2025) found that each additional 5 years of night-shift exposure is associated with a further relative risk of 1.07 for cardiovascular incidence and 1.05 for cardiovascular mortality. In plain terms, the risk gradient rises with accumulated years on nights. That makes lifetime exposure, rather than a single roster week, the quantity a schedule can influence.
- Is heart disease proven to be caused by shift work?
- No. All the inputs are observational cohort data, and Xi et al. self-rate their GRADE certainty as low to very low, so the correct reading is a strong association, not proven causation. Highly suggestive is the top tier this field reaches, because no one can randomize people to decades of night work. Note that a lack of trial-grade proof is not the same as proof of safety.
- For scheduling, does the headline risk or the dose-response matter more?
- The dose-response. The headline figures, RR 1.23 for myocardial infarction and RR 1.13 for total cardiovascular events, treat exposure as a fixed yes-or-no. The per-5-year increment of RR 1.07 for incidence identifies cumulative years as the variable a roster controls, which is the number to design around.
Sources
Every figure on this page is drawn from a cited primary source and checked against the original publication.
Wu et al. (2022). Shift work and health outcomes: an umbrella review of systematic reviews and meta-analyses. Journal of Clinical Sleep Medicine, 18(2), 653โ662. https://pmc.ncbi.nlm.nih.gov/articles/PMC8804985/
Umbrella review of 16 graded meta-analyses
Xi et al. (2025). Association between night shift work and cardiovascular disease: a systematic review and dose-response meta-analysis. Frontiers in Public Health, 131668848. https://pmc.ncbi.nlm.nih.gov/articles/PMC12506678/
Dose-response meta-analysis of 23 cohort studies (3.34M participants)
Vyas, M. V., Garg, A. X., Iansavichus, A. V., Costella, J., Donner, A., Laugsand, L. E., Janszky, I., Mrkobrada, M., Parraga, G., & Hackam, D. G. (2012). Shift work and vascular events: systematic review and meta-analysis. BMJ, 345e4800. https://doi.org/10.1136/bmj.e4800
Systematic review and meta-analysis (34 studies, 2,011,935 people)
None of the studies cited here evaluated Soon.They examine scheduling practices, shift patterns, and working hours as studied by independent researchers, so their findings describe what those practices are associated with, not what any particular software produces.
This article summarizes published research for scheduling and operations decisions. It is not medical advice. Individual health questions belong with a qualified clinician.
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