The longer you work night shifts, the higher your cardiovascular risk — switch if you can

39. The longer you work night shifts, the higher your cardiovascular risk — switch if you can

Cost: Switching jobs or changing shifts may mean a pay cut and loss of night-shift bonuses. Job hunting takes time and determination. If you factor this into your calculations when choosing a job, the cost is effectively zero.

In plain terms: People who work night shifts develop cardiovascular disease about 13% more often than those who don’t, and cardiovascular deaths rise by roughly 27%. The longer you work nights, the worse it gets: for every additional five night shifts, cardiovascular disease risk climbs another 7%. So, when you weigh the long-term costs, it makes sense to switch shifts early on. As for cancer risk, the evidence linking night shifts to cancer is far weaker than commonly believed.

Benefit: A pooled analysis of 23 studies — all observational, no subgroup adjustments — shows that night-shift workers face a roughly 13% higher risk of cardiovascular events (RR 1.13, 95% CI 1.10–1.16). Cardiovascular deaths rise by about 27% (RR 1.27, 1.18–1.36). Over time, each extra five night shifts adds roughly 7% to cardiovascular disease risk (RR 1.07, 1.04–1.09) and about 5% to cardiovascular mortality (RR 1.05, 1.03–1.06). Specific conditions show similar trends: coronary heart disease incidence rises by 22% (RR 1.22, 1.16–1.28) and mortality by the same amount; ischemic heart disease deaths increase by 39% (RR 1.39, 1.06–1.84); stroke mortality climbs by 49% (RR 1.49, 1.04–2.12). Stroke incidence, however, shows no significant rise (RR 1.06, 0.95–1.18).

Evidence grade: A

Sources: Xi J, Ma W, Tao Y, et al. (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>; Esposito G, Bravi F, Santucci C, et al. (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>; Shen QM, Li ZY, Tan YT, et al. (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>; Czeisler CA, Johnson MP, Duffy JF, et al. (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>

Notes: All these findings come from observational studies without subgroup adjustments. Night-shift workers naturally differ from others in smoking habits, weight, and income, and full adjustments are hard to achieve. Cancer risk evidence is weaker than popular claims suggest. A pooled analysis of 12 studies involving 12,132 breast cancer cases found only a 5% higher risk among night-shift workers (RR 1.05, 95% CI 0.96–1.14). After 20 years of night work, the risk rose to 25% (RR 1.25, 1.01–1.55), but this figure lost significance after accounting for publication bias; the link is “far from established.” Another long-term study of Chinese men over 16.1 years found no overall cancer link, though pancreatic cancer risk rose 59% (HR 1.59, 1.09–2.31) after 11–20 years of night work. Therefore, this analysis focuses on cardiovascular risk, not cancer. Not everyone must leave night shifts; you should weigh the long-term costs yourself. For those already working nights, several steps help: quit smoking (see Section 1); control blood pressure and cholesterol per medical advice (Section 12); and make up lost sleep after shifts (Section 38). Two additional strategies are worth trying: eat mainly during daylight hours, and use bright light during shifts plus near-total darkness during daytime rest to reset your circadian rhythm. Only the latter has proven effective at shifting the rhythm; ordinary indoor lighting leaves it unchanged even after six night shifts. Bright light at 7,000–12,000 lux combined with near-total darkness restores it in four days. Crucially, all three measures — bright night-time light, strict daytime darkness, and sunglasses on the way home — must be used together; skipping any one negates the effect. Both strategies affect metabolism and sleep only; no trials have shown they lower cardiovascular risk. On days off, returning to a daytime routine resets the rhythm again. Full numbers, sources, and details on how the body tracks time are in [docs/Biological clock and night shift.md](../../docs/research/Biological clock and night shift.md). [8202〕