Shift work spans regular nights, evenings, rotating schedules and other arrangements outside a standard daytime pattern. The available statistics show how common these schedules are, how sleep differs across groups, and what observational and trial evidence says about health, safety and schedule design.
Key Shift Work Statistics
The following figures summarize the most broadly useful measures:
- In 2021, 20.72% of 148,097,540 U.S. civilian noninstitutionalized workers were estimated to work an alternative shift.
- In 2021, 4.28% of U.S. civilian noninstitutionalized workers were estimated to work a night shift.
- In 2010, 72.6% of employed U.S. adults usually worked a regular daytime shift.
- In 2010, 44.0% of U.S. night-shift workers reported sleeping six hours or less on average.
- In 2010, about 40.6 million employed U.S. adults were estimated to have short sleep.
- In 2010, 69.7% of transportation and warehousing workers on regular nights reported short sleep.
- In 2010, 52.3% of U.S. health care and social assistance workers on regular nights reported short sleep.
- Among South Korean rotating-shift nurses in 2016, 76.4% met the study’s insomnia criterion.
- Among Norwegian shift workers in 2009, 12.8% met the study’s insomnia criterion.
- Across 29 occupational studies through 2020, shift work disorder prevalence was estimated at 26.5%.
- A 2025 meta-analysis estimated 1.42 times the odds of sleep disturbance for occupational shift workers compared with non-shift workers.
- A 2025 cardiovascular review found a relative risk of 1.13 for total cardiovascular-disease incidence among night-shift workers versus daytime workers.
- The same review found a relative risk of 1.27 for total cardiovascular mortality among night-shift workers.
- Each five-year increase in night-shift duration was associated with a 7% higher risk of cardiovascular-disease incidence.
- In an earlier review, shift work was associated with a myocardial-infarction relative risk of 1.23.
- Working more than 12 hours per day was associated with a relative risk of 1.24 for safety incidents.
- In two randomized trials, a 16-hour maximum daily shift increased off-shift sleep by 0.73 hours per day.
Contents
- How many workers work alternative and night shifts
- Worker demographics and schedule patterns
- Short sleep across shifts and industries
- Insomnia statistics across occupations and countries
- Shift work disorder and sleep outcomes
- Cardiovascular and safety outcomes
- Shift schedule and sleep-intervention data
How Many Workers Work Alternative and Night Shifts?
The 2021 NIOSH Worker Health Charts estimate covers the U.S. civilian noninstitutionalized worker population. NIOSH’s alternative-shift category is broader than night work and represents any alternative shift-work category in that dataset.
- In 2021, 30,684,089 U.S. workers, or 20.72% of 148,097,540 workers, were estimated to work an alternative shift.
- The 95% confidence interval for that alternative-shift estimate was 19.91% to 21.54%.
- In the same year, 6,338,209 workers, or 4.28%, were estimated to work a night shift.
- The 95% confidence interval for night-shift prevalence was 3.87% to 4.71%.
Source: NIOSH Worker Health Charts: Unadjusted Prevalence of Work Organization Characteristics (NHIS 2021).
The earlier 2010 CDC survey used self-reported usual shifts among employed civilian workers. Its categories are not identical to the 2021 NIOSH measures.
| Usual shift, United States | 2010 share of employed adults |
|---|---|
| Regular daytime | 72.6% |
| Regular nighttime | 3.7% |
| Evening, rotating or other | 23.5% |
Source: Short Sleep Duration Among Workers — United States, 2010. The “other” category combines regular evening, rotating and some other schedules.
Worker Demographics and Schedule Patterns
The CDC’s 2010 estimates define short sleep as an average of six hours or less in a 24-hour period. Sleep duration, work hours and shift category were self-reported, and the survey did not separate workdays from nonworkdays.
- Among 30–44-year-old U.S. workers, short sleep was reported by 51.1% on regular nights and 29.4% on regular days.
- Among 45–64-year-old U.S. workers, short sleep was reported by 46.4% on regular nights and 31.1% on regular days.
- Among workers aged 18–29, short sleep was reported by 37.4% on regular nights and 24.6% on regular days.
- Among workers aged 65 or older, 21.1% reported short sleep on regular days; the night-shift estimate was not stable enough to report.
Differences also appeared across demographic and employment groups, but these are descriptive associations rather than causal comparisons.
- Short sleep among non-Hispanic Black workers was 45.6% on regular nights, compared with 44.8% among non-Hispanic White workers.
- Among Hispanic workers, short sleep was 42.7% on regular nights and 26.4% on regular days.
- Workers with some college education reported short sleep at 54.1% on regular nights and 32.5% on regular days; the night estimate had a 44.6%–63.3% confidence interval.
- Workers with more than one job reported short sleep at 60.5% on regular nights, versus 42.2% among one-job workers.
- Among regular-night workers, short sleep was 58.1% for those working more than 40 hours weekly and 38.8% for those working 40 hours or less.
Source for these demographic and schedule-pattern estimates: Short Sleep Duration Among Workers — United States, 2010.
Short Sleep Statistics Across Shifts and Industries
In 2010, short sleep affected 30.0% of all employed U.S. adults. The CDC reported 28.8% among day-shift workers, 44.0% among night-shift workers and 31.6% among workers in other shift categories.
| Group or schedule | Short sleep, 2010 |
|---|---|
| All employed adults | 30.0% |
| Regular day shift | 28.8% |
| Regular night shift | 44.0% |
| Other shift | 31.6% |
The survey estimated approximately 40.6 million employed U.S. adults with short sleep. By sex, short sleep was 41.7% for men on regular nights and 46.6% for women on regular nights; the corresponding day-shift figures were 28.8% and 28.9%.
Industry patterns were uneven. Across all shifts, short sleep was 34.1% in U.S. manufacturing and 24.1% in other services in 2010.
- In transportation and warehousing, short sleep reached 69.7% among regular-night workers, compared with 30.8% among regular-day workers; the night estimate had a 50.8%–83.7% confidence interval.
- In health care and social assistance, short sleep was 52.3% on regular nights and 28.9% on regular days.
- In public administration, short sleep was 44.1% on regular nights and 32.9% on regular days; the night estimate had a 24.4%–65.9% confidence interval.
Source: Short Sleep Duration Among Workers — United States, 2010. These estimates use self-reported whole-hour average sleep and do not establish that shift timing alone produced the differences.
Insomnia Statistics Across Occupations and Countries
A systematic review of shift-worker studies found insomnia prevalence ranging from 12.8% to 76.4% across five studies conducted in South Korea, the United States, Iran, Norway and Japan. The percentages should not be treated as a pooled international rate because the studies used different occupations, instruments and diagnostic thresholds.
| Population and location | Period | Insomnia result |
|---|---|---|
| Rotating-shift nurses, South Korea | 2016 | 76.4% of 1,431 |
| Night workers in U.S. health institutions and industry | 2015 | 62.2% of 37 |
| Female nurses in Iranian university hospitals | 2012 | 43.1% of 160 |
| Shift workers across occupations, Norway | 2009 | 12.8% of 2,046 |
| Nursing-home shift workers, Japan | 2008 | 40.6% of 509, versus 27.6% of non-shift workers |
In the Norwegian population-based study, shift workers averaged approximately 15 minutes less sleep than day workers. In the South Korean nurse study, workers with insomnia averaged 5.2 night shifts per month, compared with 4.7 among workers without insomnia; this was a cross-sectional association, not proof that shift frequency caused insomnia.
Source: Prevalence of insomnia in shift workers: a systematic review.
Shift Work Disorder and Sleep-Outcome Data
A systematic review and meta-analysis covering 29 occupational studies published through 2020 estimated shift work disorder prevalence at 26.5%. Individual study estimates ranged from 2.3% to 84.0%, reflecting differences in populations, countries, schedules, definitions and assessment methods.
A 2025 systematic review and meta-analysis of occupational populations across eight countries found higher odds of several sleep outcomes among shift workers than comparison workers.
| Sleep outcome | Pooled association |
|---|---|
| Any sleep disturbance | Odds ratio 1.42 (95% CI 1.24–1.62) |
| Insomnia disorder | Odds ratio 1.22 (95% CI 1.08–1.39) |
| Poor sleep quality | Odds ratio 1.45 (95% CI 1.10–1.92) |
| Unspecified sleep disturbance | Odds ratio 1.75 (95% CI 1.35–2.25) |
All 22 studies in that 2025 review were cross-sectional, so these pooled associations do not prove causation. Heterogeneity was moderate for insomnia disorder at I² 45.9%, substantial for poor sleep quality at I² 79.1%, and moderate for unspecified disturbances at I² 31.8%.
The evidence base included 13 studies of rotating shifts and seven studies of permanent night shifts; two additional studies did not specify the rotation pattern. Six of nine studies reporting night-shift duration examined shifts longer than eight hours.
Sources: Prevalence of Shift Work Disorder: A Systematic Review and Meta-Analysis and Shift work and risk of sleep disturbances in occupational populations: a systematic review and meta-analysis.
Cardiovascular and Safety Outcomes
A 2025 systematic review and dose-response meta-analysis associated night-shift work with higher cardiovascular risks than daytime work. These are observational summary estimates, so residual confounding and differing cardiovascular-disease definitions remain possible.
- Total cardiovascular-disease incidence had a relative risk of 1.13 (95% CI 1.10–1.16).
- Total cardiovascular mortality had a relative risk of 1.27 (95% CI 1.18–1.36).
- Each five-year increase in night-shift duration was associated with a relative risk of 1.07 for cardiovascular-disease incidence (95% CI 1.04–1.09).
- Each five-year increase in night-shift duration was associated with a relative risk of 1.05 for cardiovascular mortality (95% CI 1.03–1.06).
- Incident coronary heart disease had a pooled relative risk of 1.22 (95% CI 1.16–1.28), while incident ischemic heart disease had a pooled relative risk of 1.09 (95% CI 1.05–1.14).
An earlier review based on evidence available through 2011 found relative risks of 1.23 for myocardial infarction and 1.24 for coronary events among shift workers versus non-shift workers. Evidence quality was graded moderate for myocardial infarction and low for coronary events.
Extended hours are related but are not the same exposure as night work. A review of studies through December 2020 found a relative risk of 1.24 for safety incidents when workers exceeded 12 hours per day; exceeding 55 hours per week also had a relative risk of 1.24, but its 95% confidence interval was 0.98–1.57.
For other extended-hours comparisons, the pooled safety-incident relative risk was 0.93 for more than eight hours per day and 1.08 for overtime work. The review rated the evidence low certainty, and these estimates should not be read as direct night-shift effects.
Sources: Association between night shift work and cardiovascular disease: a systematic review and dose-response meta-analysis, Shift work and vascular events: systematic review and meta-analysis, and Safety incidents associated with extended working hours: A systematic review and meta-analysis.
Shift Schedule and Sleep-Intervention Data
The schedule-intervention evidence concerns specific trials rather than all shift workers. A Cochrane review often rated this evidence low or very low certainty, so individual estimates are best understood as trial findings rather than universal effects.
- In two randomized trials among workers in 80-hour workweek settings, a 16-hour maximum daily shift increased off-shift sleep by 0.73 hours per day (95% CI 0.30–1.13) versus no daily limit.
- The same 16-hour limit reduced on-shift sleepiness by 0.37 points on the Karolinska Sleepiness Scale (95% CI −0.55 to −0.17).
- In one non-randomized trial, forward versus backward rotation produced a mean sleep-quality difference of −0.20 points on the Basic Nordic Sleep Questionnaire (95% CI −2.28 to 1.89).
- Forward versus backward rotation produced a mean off-shift sleep-length difference of −0.21 hours (95% CI −3.29 to 2.88) in a comparison with only 62 participants.
- Across three comparative studies, shorter 8–10-hour shifts showed a standardized reduction in sleepiness during shifts, while sleep-quality results were not clearly different; the sleep-quality standardized mean difference was −0.23 (95% CI −0.61 to 0.15).
- For shorter versus longer shifts, one review estimate showed 0.26 hours less off-shift sleep per day for the shorter-shift comparison; the standardized mean difference was 0.18 (95% CI −0.17 to 0.54), with very low-certainty evidence.
- More compressed versus more spread-out schedules showed a mean off-shift sleep-duration difference of 0.52 hours (95% CI −0.52 to 1.56), with the confidence interval crossing zero.
Source: Adapting shift work schedules for sleep quality, sleep duration, and sleepiness in shift workers.