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

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.

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.

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).

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〕

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