# Prevalence of Overnight Work (1 a.m. to 5 a.m.) Among United States Workers

## TL;DR

This study estimates that 14.2% of U.S. workers did overnight shifts between 1 a.m. and 5 a.m. in 2015, with significant variations across demographics and industries.

## Contribution

The study provides the first national estimates of overnight work in the U.S. using a precise circadian-based definition.

## Key findings

- Over 21 million U.S. workers experienced overnight work in 2015.
- Industries like Transportation and Protective Services had the highest prevalence of overnight workers.
- Overnight workers were more likely to sleep less than 7 hours or more than 9 hours.

## Abstract

Many factors have resulted in the normalization of nonstandard work schedules in recent decades, including globalization requiring working across time zones and growing demands for goods and services. This paper provides national estimates of overnight work in the USA.

We used cross‐sectional data from the 2015 National Health Interview Survey (n = 19,386 US employed adults ≥ 18 years). This survey contained a unique definition of overnight work (i.e., between 1:00 a.m. and 5:00 a.m.), based on the window of circadian low. Weighted prevalence rates were provided across categories of sociodemographic characteristics, health status, health behaviors, and occupational factors.

We estimated more than 21 million US employed adults experienced overnight work (14.2%). Higher prevalence was found among men (17.8%), non‐Hispanic Black adults (17.2%), non‐US born adults (11.2%), those with some college (15.9%) or a high school (16.7%) education, or living in the Midwest region (15.8%). Compared to those sleeping 7–9 h (10.5%), higher percentages of adults working overnight slept < 7 h (21.4%) and > 9 h (17.0%). Increasing prevalence was observed with increasing weekly work hours (p < 0.0001). Higher prevalence was reported among multiple job holders (19.5%). Industries and occupations with the greatest percentage of overnight workers were Transportation, Warehousing and Utilities (29.3%), and Protective Services (47.4%).

Our estimates of overnight work in 2015 are almost five times higher than estimates from 2004. Given that overnight work has been associated with adverse safety and health outcomes, additional policies and programs are needed to protect this growing population of workers.