Long Working Hours and Health: What Large Studies Found

You agreed to a heavy quarter: late nights until the launch, then back to normal. The launch slipped, a new one arrived, and a year later the long weeks are simply how the job works. You feel tired but fine. The question the large studies ask is what years of weeks like that do to the heart and brain.

The research on long working hours and health gives a clearer answer for the circulation than for the mind. In 2020, systematic reviewssystematic review: A review that fixes its question and its rules for including studies in advance, then searches out every study that fits and weighs them together. Some systematic reviews pool the results into a meta-analysis; others describe what the studies found without combining the numbers.Full entry in the glossary run for the World Health Organization (WHO) and the International Labour Organization (ILO) found sufficient evidence of harm from working 55 hours a week or more, linking it to a higher risk of stroke and ischemic heart disease, and rated that evidence moderate quality.¹² The main published critique targets the heart-disease link rather than the stroke one, and the evidence on depression is too weak to call. For your own week, the findings point to four modest steps, set out below: count your real hours, keep crunch periods temporary, protect sleep and have your blood pressure checked.

This is one strand of a wider question, what work-life balance means in research; here the focus is only on hours and health.

What the WHO and ILO estimated, and how they did it

The WHO/ILO Joint Estimates, published by Frank Pega and colleagues in Environment International in 2021, combined two things: how many people around the world work 55 hours a week or more, and how much higher their risk of stroke and ischemic heart disease was according to the two systematic reviews. From the two, the team calculated the share of those diseases that long hours may account for, then applied that share to WHO’s estimates of all deaths from them.³

The logic is the one public-health agencies use for smoking or air pollution. A risk that is small for each person can still add up to a large number when hundreds of millions of people carry it. A town where one in ten adults smokes loses more people to smoking than a town where one in fifty does, even though each smoker’s risk is the same.

The study

Moderate evidence

What WHO and the ILO modelled for 2016

About 488 million people, roughly 9% of the world’s population, worked 55 hours a week or more in 2016. WHO and the ILO attributed about 745,000 deaths from stroke and ischemic heart disease that year to those hours, about 5% of all deaths from the two diseases, and called long hours the occupational risk with the largest attributable disease burden in their assessment. Men, people in middle and later working age, and the South-East Asia and Western Pacific regions carried more of it.³

The number is an estimate, not a count of death certificates that list overwork. It holds only if the risk figures from the reviews reflect cause and effect, and those figures come from observational studiesobservational study: A study in which researchers record what people already do or are exposed to, rather than assigning anyone to anything. It can show that two things go together, not that one causes the other, because the groups being compared may differ in other ways as well.Full entry in the glossary, in which hidden differences between long-hours and standard-hours workers can never be fully ruled out.

For your own week, the lesson is narrower. A population figure cannot tell you your own odds; it says long hours are common enough, and risky enough, to matter for public health. The next section puts the risk in one person’s terms.

How much higher is one person’s risk?

For an individual worker the added risk is modest. The WHO/ILO reviews found that, compared with a standard full-time week, working 55 hours or more went with about a third more strokes and about a sixth more deaths from ischemic heart disease (in the heart review’s own illustration, roughly 18 rather than 15 cases a year per 10,000 workers), in studies that followed people for anywhere from one year to several decades.²¹

Relative figures sound larger than they are when the disease is uncommon. In an earlier pooling, Mika Kivimäki and colleagues’ 2015 Lancet analysis of cohorts from Europe, the US and Australia, about 3 in 1,000 working adults had a stroke over an average of about seven years, and the team concluded that people who work long hours deserve more attention to their vascular risk factors.⁴ That rate mixes long and standard hours, so this is only rough arithmetic of our own: a risk a third higher on that base adds about one stroke per 1,000 people over the same period. Across a large workforce that is a real toll; for one person it is a reason to look at risk factors, not a forecast.

Why would hours matter at all? The WHO/ILO team describes two proposed routes: a prolonged stress response that strains the heart and blood vessels, and the habits long weeks crowd in, such as smoking, heavy drinking, poor diet, too little exercise and short sleep. Neither route is proven. The model also assumed a lag of about a decade between long hours and disease, in line with how long the studies behind it followed people, and a French cohort saw raised risk only a decade after long hours, not before.³

Relative figures sound larger than they are when the disease is uncommon.

Consider a project lead in a year of back-to-back launches. Lunch moves to the desk, the evening walk disappears and a routine check-up is postponed twice. None of that shows in a count of hours, yet it is the second route the researchers describe, and it is the part most within reach.

If long weeks are your normal, a blood pressure check is a sensible first step; the last section explains why and where to get one.

Where critics say the estimate goes too far

One detailed critique came from the epidemiologist who led the 2015 Lancet analysis. In a 2020 commentary, Kivimäki and three colleagues argued that the WHO/ILO experts had misapplied their own rating framework for heart disease: the link was stronger in the lower-quality studies and not statistically significant in the higher-quality ones. They also found no excess heart risk among people in high-status occupations who worked long hours, and proposed that the conclusion be limited to lower-status jobs.⁵ The WHO/ILO authors acknowledged the disagreement and judged the evidence on job status too thin, and too concentrated in Europe, to use for global estimates.³

Later data added more doubt. A 2024 editorial in the Scandinavian Journal of Work, Environment and Health by Reiner Rugulies, who led the WHO/ILO review on depression, describes Danish register studies that found no raised heart risk with long hours overall (defined there as more than 48 hours a week), a raised risk that appeared only among lower-status workers, and a link with hemorrhagic (bleeding) strokes but not with strokes in general, a split later seen in a French cohort too. Why would job status matter? One explanation the editorial offers is that what happens inside the hours may count as well as how many there are.⁶ Sixty hours of self-directed work, with money for good food and a gym, differ from sixty hours of physical shifts with little say over breaks.

Beyond the heart: mood, sleep and safety

The evidence outside cardiovascular disease is mixed and mostly weaker. A 2021 WHO/ILO systematic review of cohort studies judged the evidence inadequate to say whether long hours cause depression, and concluded that estimating a burden of depression from long hours would not be evidence-based.⁷

That is not the same as “no effect.” A 2024 review by Mikko Härmä and colleagues notes that people who work long hours report more psychological distress, while two large Danish studies found that longer weeks did not predict use of psychiatric medicines or hospital treatment. Feeling worn down is real even when it does not add up to a diagnosis. Sleep and fatigue are where the everyday cost shows most clearly. The same review concludes that long hours and shift work, which often come with night work and too little recovery time, go with poorer sleep, more fatigue and more sickness absence, and that very long weeks tend to go with more safety incidents while moderately long ones do not.⁸ For someone who drives home after a very long shift, that is the practical risk to watch today, long before any effect on the heart.

1. 35 to 40 hours a week: the standard week that every other band was compared with
2. 41 to 48 hours: evidence of harm judged inadequate for both ischemic heart disease and stroke
3. 49 to 54 hours: inadequate for ischemic heart disease; limited for new strokes
4. 55 hours or more: sufficient evidence of harm for ischemic heart disease and for new strokes, rated moderate quality

Side by side, the five outcomes line up like this.

Read down the table and the practical order is plain: sleep and fatigue are the costs you can act on this month, and the stroke and heart findings are the reason not to let a crunch become permanent.

Long working hours and health: what lowers the risk

The most direct remedy is the obvious one, and it has some trial evidence behind it. The 2024 Härmä review concludes that the health risks of long hours can be reduced by working less, and points to a randomized trial where a shorter working week reduced sleep problems, stress and fatigue. Control matters as well as quantity: the same review describes growing evidence that a say over when you start, finish and take time off supports health and recovery, and may soften the effect of overtime.⁸ A long stretch you chose, with a clear end date, differs from one set by someone else with no end in sight.

In practice, the evidence suggests a few habits, none of them tested as a package:

• Count your real hours. For a month, note when you start and stop, including evening email; the studies relied on people’s own estimates, and weeks that feel normal can quietly cross 55.
• Put an end date on every crunch period and treat it as a checkpoint. If the date passes and the hours stay, the stretch has become the job.
• Protect sleep. Poorer sleep is a well-documented cost of long hours, and one you notice day to day; these habits that help you sleep better are a place to start.
• Keep the basics that long weeks crowd out: a real lunch break, some movement most days and a routine check-up.

For managers, the fix sits at team level. The 2021 WHO/ILO paper calls for working-time limits, with hours set, monitored and enforced so that working time does not damage health.³ Workload and control are also the first levers in what employers can do for employee wellbeing.

Symptoms that need a doctor, and how soon

Long hours themselves are not a medical emergency, but some symptoms are, whatever their cause. The tiers below draw on guidance from the US CDC and NIMH and from the NHS in the UK; the three tiers are our own grouping.

• Now: sudden face drooping, arm weakness or slurred speech are signs of stroke, and chest pain or pressure, especially spreading to the arm, neck or jaw, can mean a heart attack. Call 911 in the US or 999 in the UK, even if the symptoms pass; do not drive yourself.^10111213 When thoughts of suicide or self-harm arise, US readers can reach the 988 Suicide and Crisis Lifeline (call or text) or dial 911 in a life-threatening emergency; UK readers can go to A&E, call 999 or talk to Samaritans on 116 123.¹⁴¹⁵ Outside the US and UK, use your local emergency number. If a long shift leaves you too drowsy to drive safely, do not drive: the UK Highway Code, updated in 2025, warns that driving tired sharply raises the risk of a crash.¹⁶
• Soon, within days or weeks: see a doctor if low mood, anxiety or poor sleep will not lift. The NHS notes that a GP can advise on treatments and help you reach mental health services, and in England needs that are urgent but not life-threatening can go to an urgent GP appointment or to NHS 111.¹⁵
• Routine: if you regularly work long weeks, ask for a blood pressure check at your next appointment. The NHS notes that high blood pressure usually causes no symptoms but can lead to strokes and heart disease; in England many pharmacies offer free checks for people aged 40 or over, and elsewhere a doctor or pharmacist can advise.¹⁷

The bottom line

The strongest large studies link weeks of 55 hours or more, kept up for years, to more strokes and possibly more heart disease; the added risk for any one person is small, and experts still argue about how much of it long hours cause. Poorer sleep and fatigue are the costs you can see now. If long weeks have become your normal, count them honestly, protect sleep, and ask for a blood pressure check.