How Shift Workers’ Internal Clock Affects Their Health

A Rutgers Health sleep expert explains how biological predispositions toward morning or evening alertness determine how well a health care professional adapts to shift schedules

Health care workers who take on extended or overnight shifts, particularly during periods of operational strain, may face heightened fatigue that can affect their own well-being. This fatigue arises not from individual effort or commitment, but from the physiological challenges created when work demands intersect with the body's internal clock.

"Fatigue isn't just about being tired," said Suzanne Crincoli, an assistant professor in the division of nursing science at the Rutgers School of Nursing. "It's about biology." Crincoli, who researches the effects of acute and chronic fatigue among health care providers and shift workers, discusses the challenges of health care shift work and strategies to combat fatigue.

What are the dangers of acute and chronic fatigue in health care settings?

Acute fatigue, such as working long shifts or consecutive nights, can immediately impair attention, reaction time and decision-making, especially after long hours. Chronic fatigue is more insidious. It represents a cumulative physiological debt that affects emotional regulation and physical health over time - over 27% reported anxiety or depression when chronically fatigued.

In our studyof frontline nursing professionals, chronic fatigue was the single strongest predictor of burnout, explaining over 50% of the variability in burnout scores, far outweighing staffing levels or workload alone. Chronic fatigue was also associated with circadian disruption, increased cardiometabolic risk, including obesity and hypertension.

How could night shifts affect workers?

Night shifts place workers in direct opposition to their biological clocks, leading to reduced vigilance and slower reaction times, especially during the early morning hours when the circadian drive for sleep is strongest. While our study found that operational factors, such as workload and patient volume, were stronger predictors of missed nursing care than fatigue alone, night work still significantly increases safety risks, particularly outside the clinical setting.

Health care workers on night shifts reported substantially higher rates of drowsy driving, a major contributor to motor vehicle crashes after shifts. This risk was especially pronounced for workers whose biological timing was mismatched with their assigned shifts.

What are the risks of fatigue among nurses, health care providers and first responders?

Workers whose chronotype was misaligned with their shifts experienced markedly higher health and safety risks.

Suzanne Crincoli

Assistant Professor, Rutgers School of Nursing

Fatigue affects safety, health and long-term career sustainability. In nurses, health care providers and first responders, fatigue has been linked to increased risk of medical errors and injuries, higher rates of burnout and mental health disorders, greater likelihood of cardiometabolic disease, including obesity and diabetes, and impaired immune function and increased infection risk.

Our findings show that these risks are highly variable among individuals. They depend heavily on chronotype, or an individual's biological timing. For example, some workers experienced higher metabolic risk, while others experienced higher safety and mental health risk, even when working the same shift.

What is the role of chronotype and circadian rhythms in shift-work adaptation?

Chronotype reflects whether someone is biologically predisposed toward earlier - morning lark - or later - night owl - sleep and alertness patterns. It is genetically anchored, not a matter of preference or motivation.

Our studyidentified four distinct chronotype-shift profiles, each with different risk patterns. Workers whose chronotype was misaligned with their shifts experienced markedly higher health and safety risks. For example, morning-type individuals working night shifts had the highest rates of drowsy driving and mental health diagnoses, while evening-type individuals working day shifts showed the highest cardiometabolic risk, including obesity and elevated blood sugar.

This demonstrates that circadian mismatch, not simply working nights, is a key driver of harm.

What are some strategies health care workers can take to reduce occupational fatigue?

While there is no one-size-fits-all solution, there are evidence-based strategies that can significantly reduce risk. When possible, health care workers can align their shifts with their chronotype to reduce circadian strain and limit consecutive night shifts and allow adequate recovery time between shifts. They can protect their sleep opportunity, especially after night shifts, by using light control and consistent routines.

Strategic napping and caffeine use can improve alertness without disrupting recovery sleep. For example, they can take a "nappucino" by drinking a cup of coffee and taking a 15- to 20-minute nap. The rest plus caffeine will provide a jolt of energy without too much physiologic disruption.

Organizational policies that recognize fatigue as a biological risk, not a performance issue, also are critical.

Explore more of the ways Rutgers research is shaping the future.