Circadian rhythm, shift work, and metabolic risk

Why does night shift work disrupt circadian rhythm?

Circadian rhythm is the body’s internal 24-hour clock. It regulates when we sleep and wake, but also plays a central role in metabolic processes such as glucose control, lipid metabolism, blood pressure regulation and hormone release.

Under normal conditions, circadian rhythm is synchronised by external cues — particularly light and darkness — and reinforced by regular patterns of sleep, meals and activity.

Shift work disrupts this alignment in several ways:

• Light exposure at the wrong biological time, particularly overnight, suppresses melatonin and alters circadian signalling
• Irregular sleep timing, even when total sleep duration is adequate, weakens circadian stability
• Rotating schedules prevent the body clock from fully adapting in either direction
• Meal timing shifts — often later at night — conflict with metabolic rhythms optimised for daytime eating

The result is chronic circadian misalignment — a persistent mismatch between biological timing and external demands. This disruption does not disappear with experience. Even long-term night shift workers rarely achieve full circadian adaptation, particularly when schedules rotate.

How does circadian disruption affect metabolic health?

Circadian rhythm is tightly linked to metabolic regulation. When that rhythm is repeatedly disrupted, metabolic health is affected at multiple levels.

Research consistently links night shift work to higher rates of:

• Obesity and central adiposity (fat around the midline, which is particularly dangerous to health)
• Insulin resistance and type 2 diabetes
• Dyslipidaemia, including high triglycerides and low HDL cholesterol
• Hypertension
• Cardiovascular disease and stroke

A major 2025 meta-analysis found that night shift workers had a significantly increased risk of cardiovascular events, with a clear dose–response relationship: every additional five years of night shift work further increased risk. 

These effects are driven by a combination of biological and behavioural factors — including hormonal dysregulation, sleep restriction, stress responses, irregular meal timing and reduced opportunity for physical activity.

Crucially, metabolic risk often develops years before clinical diagnosis.

Circadian disruption is now recognised as a cardiometabolic risk factor

In 2025, the American Heart Association formally recognised circadian disruption as a modifiable cardiometabolic risk factor.

Their recent statement highlights that:

• Sleep timing regularity matters as much as sleep duration
• Shift work and social jetlag contribute directly to metabolic risk
• Circadian metrics may need to be incorporated into future risk models

This represents an important shift in thinking, from viewing circadian disruption as a lifestyle inconvenience to recognising it as a modifiable occupational health exposure, particularly relevant for night shift and frontline workers.

What is the current regulation and guidance for night shift workers?

In the UK, shift work is increasingly recognised within occupational health and safety frameworks.

Guidance from NHS Employers and the Society of Occupational Medicine describes circadian disruption and fatigue as workplace hazards, particularly in safety-critical environments. Recommendations commonly include:

• Forward-rotating shift patterns (early → late → night)
• Limiting consecutive night shifts
• Avoiding very early starts where possible
• Ensuring adequate recovery time between shifts
• Providing regular health assessments for night workers
• Treating shift work as a risk factor within health surveillance

While much of this guidance has historically focused on fatigue and safety, there is growing convergence with clinical evidence on metabolic health.

The implication is clear: prevention is not only an individual responsibility — it is also a matter of job design and organisational risk management.

What does Qured see in metabolic health screening?

Across Qured’s metabolic health screening programmes for shift-based and safety-critical workforces, night shift workers consistently show poorer metabolic profiles than day workers.

Key patterns include:

• Higher triglyceride levels
• Lower HDL (“good”) cholesterol
• Worse liver function test results
• Higher prevalence of metabolic syndrome markers

In aggregated Qured data:

• Night shift workers are >30% more likely to have metabolic syndrome marker abnormalities
• Frontline workers (where we typically see night shifts) are >40% more likely to have high triglycerides

These differences appear even after accounting for age, and often emerge before individuals consider themselves unwell.

In practical terms, this means risk is accumulating silently within the workforce, outside of traditional triggers for action such as sickness absence or safety incidents.

This aligns closely with the wider scientific literature — and reinforces that circadian disruption shows up biologically long before diagnosis or absence.

Who is most affected?

Night shift work is more common in frontline, physically demanding and male-dominated roles.

Men, on average, also show poorer metabolic health markers than women, including higher rates of dyslipidaemia and liver enzyme abnormalities. They are more likely to work night shifts, consume more alcohol, and face structural barriers to accessing routine healthcare, which compounds risk, especially in safety-critical industries.

Why should employers care about metabolic health in shift workers?

For employers, metabolic health is not just a clinical issue — it is a workforce risk issue.

Poor metabolic health is associated with:

• Presenteeism and reduced capacity
• Increased accident risk
• Long-term sickness absence
• Higher occupational health costs
• Skills loss and replacement pressure

Absence data is a lagging indicator. By the time it changes, employees are already on the path to disease, and often multiple co-morbidities, which make it even harder to return to health and full time employment. Employers who rely on shift-based workforces therefore have a strong interest in identifying and reducing risk earlier, when intervention is more effective and less disruptive. 

What should employers do?

The emerging consensus from clinical and occupational sources is not about quick fixes — but about prevention, smart benefit design and early intervention.

Key principles include:

1. Recognise circadian disruption as a risk factor
Treat shift work itself as a contributor to metabolic risk, not just individual behaviour.

2. Design shifts with circadian health in mind
Where possible, use forward-rotating schedules, limit consecutive night shifts, and avoid very early starts.

3. Screen earlier, not later
Metabolic risk often appears years before diagnosis. Proactive blood screening helps identify issues when they are still reversible.

4. Focus on access and relevance
Frontline and night workers face different barriers. Health initiatives need to meet people where they are - for example providing services out of hours and at home.

5. Integrate prevention into risk management
Circadian health belongs alongside fatigue risk management, not separate from it.

Reframing prevention for shift-based workforces

Circadian disruption is becoming a recognised driver of cardiometabolic risk — particularly in night shift workers.

For employers, this shifts the conversation from reactive healthcare to proactive risk reduction.

Prevention, in this context, is not about asking individuals to do more. It is about understanding how work patterns shape health — and intervening earlier.

Sources & further reading

• American Heart Association (2025) — Scientific statement recognising circadian disruption as a modifiable cardiometabolic risk factor, with implications for future risk models and prevention strategies.
• Xi et al., 2025 (meta-analysis) — Evidence linking night shift work to increased cardiovascular disease risk, with a dose–response relationship by duration of night work exposure.
• Minonzio, M. et al; Work and Health 2025, Night Shift Work, Diet, Meal Timing, and Cardiometabolic Risk: An Exploratory Cross-Sectional Study in Italian Cement Workers.
• Alseedi, et al,(GLU24/7 study, 2025) — Protocol for examination cardiometabolic health risk factors in night shift workers
• NHS Employers (2025) — Guidance on health, safety and wellbeing of shift workers, highlighting circadian disruption and fatigue as workplace hazards.
• Society of Occupational Medicine (2025) — Occupational guidance on shift work, diet and health risk assessment.
  

The Qured insights referenced are based on aggregated, anonymised data from metabolic health screening programmes delivered across safety-critical and frontline industries in the UK.