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The longer you work night shifts, the higher your cardiovascular risk; if you can move to another position, do it sooner

  • Moderate value
  • Evidence A
  • Buys life
  • Costs a lot
  • Takes some hours
  • Long-term effort

In plain words

People who work night shifts have about 13% more cardiovascular disease and about 27% more cardiovascular death than people who don't. And it adds up with years: every additional 5 years of night shifts adds about 7% more cardiovascular disease. So count it in years, and if you can move to another position, do it sooner. As for night shifts causing cancer, the evidence is much softer than what is commonly said.

Cost

Moving to another position or changing jobs may mean lower pay, and the night-shift allowance is gone too. Finding a job takes time, and making up your mind is hard. If you factor this in when choosing a job, the cost is zero.

What you get

Pooling 23 follow-up studies, observational and not assigning groups: people who worked night shifts had about 13% higher risk of cardiovascular events (RR 1.13, 95% CI 1.10–1.16, the plausible range). Cardiovascular death was about 27% higher (RR 1.27, 1.18–1.36). By years: every additional 5 years of night shifts raised the incidence of cardiovascular disease by about 7% more (RR 1.07, 1.04–1.09) and cardiovascular death by about 5% more (RR 1.05, 1.03–1.06). By disease: coronary heart disease incidence was about 22% higher (1.22, 1.16–1.28), coronary heart disease death about 22% higher (1.22, 1.10–1.36), ischemic heart disease death about 39% higher (1.39, 1.06–1.84) and stroke death about 49% higher (1.49, 1.04–2.12). Stroke incidence was not significant (1.06, 0.95–1.18).

Notes

All of these are observational studies, not assigning groups. People who work night shifts already differ from others in smoking, weight and income, and the adjustment is not complete. On night shifts causing cancer, the evidence is much softer than what is commonly said. In a pooled analysis of 12 studies and 12,132 breast cancer cases, people who had worked night shifts had only about 5% higher risk, and the plausible range crossed 1 (RR 1.05, 0.96–1.14). The group with a full 20 years was about 25% higher (1.25, 1.01–1.55), but after the authors ran an influence analysis this result was no longer significant, and after adjusting for possible publication bias it was close to 1; in their words the association is “far from established.” Another study followed Chinese men for 16.1 years with 8,202 cancer cases, and found no association between night shifts and total cancer or most common cancers; only pancreatic cancer was about 59% higher in the group with a cumulative 11 to 20 years (HR 1.59, 1.09–2.31). So this item does its accounting on cardiovascular disease, not cancer. Not everyone should leave a night-shift job; the accounting by years is something you have to do yourself. If you are already working nights, first change what you can: for quitting smoking see §2.1 (quit smoking, and the earlier the better), for blood pressure and cholesterol see §2.12 (if you have high blood pressure or high cholesterol, take your medicine regularly as prescribed), and for how to catch up on sleep after a night shift see §2.38 (catch up on sleep the night after a late night). Two other strategies can be tried: concentrating eating in the daytime, and shifting the body clock with bright light plus strict blocking of daylight. The latter is the only method shown to actually move the body clock. Under ordinary indoor lighting, six night shifts in a row left the body clock unmoved; with bright light of 7000 to 12000 lux plus near-total darkness in the daytime, it flipped completely within four days. Light at night has to be bright enough, daytime sleep has to be strictly shaded from light, and you need sunglasses on the way home to block the morning light; all three are needed, and missing the last one wastes the rest. For both strategies the end points go only as far as metabolic markers and sleep; no trial has measured whether following them lowers cardiovascular risk. If you go back to a daytime life on days off, the clock gets knocked back again. The doses, the original numbers and the other sources, along with how the body tells time, are in docs/生物钟和夜班.md.

Evidence grade
A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.
Sources
  1. Xi J, Ma W, Tao Y, 等 (2025). Association between night shift work and cardiovascular disease: a systematic review and dose-response meta-analysis. Frontiers in Public Health. https://doi.org/10.3389/fpubh.2025.1668848
  2. Esposito G, Bravi F, Santucci C, 等 (2025). Night shift work and breast cancer risk in healthcare workers: a systematic review and meta-analysis. Occupational Medicine. https://doi.org/10.1093/occmed/kqaf040
  3. Shen QM, Li ZY, Tan YT, 等 (2026). Night shift work and risk of total and site-specific cancer: results from a prospective cohort study among Chinese men. Scandinavian Journal of Work, Environment & Health. https://doi.org/10.5271/sjweh.4290
  4. Czeisler CA, Johnson MP, Duffy JF, 等 (1990). Exposure to bright light and darkness to treat physiologic maladaptation to night work. New England Journal of Medicine, 322(18), 1253-1259. https://doi.org/10.1056/NEJM199005033221801

Translated from the Chinese original. Original book, section 2, tip 39. This section is about health and medicines. It is general information, not a substitute for a doctor’s diagnosis or prescription. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer