Who Gets Sick, and Where

TL;DR. Disease is not distributed randomly. What kills a 60-year-old in Japan is not what kills a 60-year-old in Chad, and the reasons are historical and economic before they are biological. Over the last century most of the world has moved through an epidemiological transition: as sanitation, nutrition, and vaccination reduce deaths from infection and childbirth, more people live long enough to develop heart disease, cancer, and dementia. That transition is a triumph, and it produces a strange result: the top causes of death in most countries are now the diseases of survival. The remaining injustice is not that rich countries die of cancer and poor countries die of infection. It is that poor countries now die of both, earlier, with a fraction of the resources.

Key takeaways

• Global life expectancy is roughly 73 years, up from about 46 in 1950. The gap between the longest-lived and shortest-lived countries is around 30 years.
• Noncommunicable diseases now cause roughly three-quarters of all deaths worldwide, including the majority of deaths in most low- and middle-income countries.
• Ischaemic heart disease and stroke are the top two causes of death globally, together around a fifth of all deaths.
• Under-5 deaths have fallen from about 20 million a year in 1950 to under 5 million, one of the largest improvements in human history, and most of the remainder are preventable.
• Only about half of the world's deaths are registered with a recorded cause, so most global health statistics are modelled estimates rather than counts.
• Within countries, the gap in life expectancy between richest and poorest neighbourhoods can exceed 15 to 20 years, sometimes across a few kilometres.

The epidemiological transition

In short: As infection and childbirth stop killing people, they live long enough to develop heart disease, cancer, and dementia, and that shift is a triumph rather than a decline.

In 1900, in the wealthiest countries on earth, the leading causes of death were pneumonia, tuberculosis, and diarrhoeal disease. Roughly one child in five did not reach their fifth birthday. Life expectancy at birth was in the forties, dragged down mostly by deaths in infancy.

Abdel Omran described the pattern of change in 1971 as the epidemiological transition, and its stages are recognisable everywhere:

The mechanism is not primarily medical. The great mortality decline in Europe and North America happened mostly before antibiotics, vaccines against most diseases, or effective cardiac care: it came from clean water, sewerage, better nutrition, less crowded housing, and food safety regulation. Thomas McKeown made this argument forcefully in the 1970s, overstating the case against medicine in ways later historians corrected, and the core point stands. Medicine matters most in the later stages; infrastructure and income mattered most in the earlier ones.

What kills people now

In short: Heart disease and stroke lead everywhere, and noncommunicable diseases now cause about three-quarters of all deaths, most of them in poorer countries.

Globally, the leading causes of death (WHO estimates, most recent full year available) are led by cardiovascular and respiratory conditions:

COVID-19 displaced this ranking entirely in 2020 and 2021, becoming one of the top causes of death worldwide, and then fell back down the list as immunity accumulated. It was the largest single disruption to global mortality patterns since the 1918 influenza pandemic, and it also reversed a decade of gains in life expectancy in many countries, most of which have since been recovered.

Noncommunicable diseases (cardiovascular, cancer, chronic respiratory, diabetes) now account for roughly three-quarters of all deaths, and, contrary to the persistent image of them as diseases of affluence, the majority of those deaths occur in low- and middle-income countries, and they occur at younger ages there.

The same disease, different countries

In short: The biology is identical and the outcome is set by whether the health system can deliver a known treatment.

The clearest way to see inequity is not in which diseases exist but in what happens to the people who get them.

The disease biology is identical. The outcome is set by whether the health system can deliver a known treatment.

Health spending explains much of it. Per-person annual health expenditure ranges from over 12,000 US dollars in the highest-spending countries to under 50 dollars in the lowest. The WHO estimates a global shortfall of millions of health workers, concentrated in Africa and Southeast Asia, and the shortage is worsened by emigration of trained staff to higher-income countries, which is effectively a transfer of subsidised training from poor countries to rich ones.

Death by age

In short: A single national top-ten list hides everything, because what kills a newborn, a 20-year-old, and a 70-year-old have almost nothing in common.

The causes of death at each stage of life are so different that a single national "top ten" hides more than it shows.

Two of these deserve emphasis. Road traffic injury kills roughly 1.2 million people a year and is the leading killer of young people worldwide, with over 90 percent of deaths in low- and middle-income countries that own a minority of the world's vehicles. It is one of the most solvable problems in this chapter: speed limits, seatbelts, helmets, drink-driving enforcement, and road design have cut deaths dramatically wherever they are applied.

And suicide kills over 700,000 people a year and ranks among the leading causes of death in young adults nearly everywhere, including in countries where every other cause has fallen.

Children and mothers

In short: Child deaths have fallen from about 20 million a year to under 5 million, while progress on maternal deaths has stalled since 2016.

The two clearest measures of a health system are how many children die before age 5 and how many women die giving birth.

Under-5 mortality has fallen from roughly 20 million deaths a year in 1950 to under 5 million now, while the world's population tripled. The global under-5 mortality rate has fallen by more than half since 2000. This is arguably the single largest improvement in human welfare in the period, and it is barely reported because it happened gradually. The remaining deaths are concentrated in sub-Saharan Africa and southern Asia, and the causes are prematurity, birth complications, pneumonia, diarrhoea, and malaria, all of which have known, cheap interventions.

Maternal mortality stands at roughly 260,000 deaths a year, with a global ratio of about 200 deaths per 100,000 live births. The distribution is extreme: roughly 70 percent of maternal deaths occur in sub-Saharan Africa, and the lifetime risk of maternal death ranges from about 1 in 10,000 in the highest-income countries to under 1 in 50 in the worst-affected ones. The causes are haemorrhage, hypertensive disorders (pre-eclampsia and eclampsia), sepsis, unsafe abortion, and obstructed labour, and every one of them has a well-established treatment. Progress on maternal mortality has stalled since about 2016 after two decades of decline.

The United States is a specific anomaly worth noting: it has the highest maternal mortality of any high-income country, with rates several times those of comparable nations and a roughly three-fold higher rate among Black women than white women, a disparity that persists after adjusting for income and education.

The gradient within countries

In short: Mortality worsens at every step down a social hierarchy, not just at the bottom, and neighbourhoods a few kilometres apart can differ by 15 to 20 years of life.

Between-country inequality is easy to see. Within-country inequality is larger than most people expect and follows a consistent pattern.

The Whitehall studies, following British civil servants from 1967 onward, found that mortality tracked employment grade in a smooth gradient: each step down the hierarchy had higher mortality than the step above, all the way up. It was not simply that the poorest did worst. Everyone did worse than the person above them, and the gradient persisted after adjusting for smoking, cholesterol, and blood pressure. Michael Marmot's interpretation, developed over subsequent decades, emphasises control over one's work and life, and social position itself, as causal factors.

The practical consequence is visible on any city map. Life expectancy differences of 15 to 20 years between neighbourhoods a few kilometres apart have been documented in London, Glasgow, Baltimore, Chicago, and many other cities. The mechanisms are cumulative: air quality, housing, food environment, exposure to violence, chronic stress, education, employment security, and access to care, each contributing a few years.

Behaviour is part of it and is itself socially patterned. Smoking, poor diet, and inactivity are more common in poorer populations, and they are shaped by price, marketing, availability, working hours, and stress. Treating them as free-floating individual choices is both empirically wrong and strategically useless, since interventions aimed only at individual behaviour tend to widen inequalities: the better-off adopt them first.

Sex and gender

In short: Women live longer and report more illness, and women were routinely excluded from clinical trials until the 1990s.

Women live longer than men essentially everywhere, by roughly 5 years globally, with the gap ranging from about 2 to 3 years in some countries to over 10 in others (notably in parts of the former Soviet Union, where male alcohol-related mortality is very high).

The gap has biological components (oestrogen's cardiovascular effects before menopause, X chromosome redundancy, lower baseline risk-taking) and large behavioural and social ones (smoking, alcohol, occupational hazard, violence, and lower health-seeking behaviour in men).

The counterpart is that women report more illness and disability at every age: more autoimmune disease, more depression and anxiety diagnoses, more musculoskeletal pain, and more years lived with disability. The summary, "women get sicker, men die quicker," is crude and empirically supported.

Medicine's historical treatment of this is a genuine problem rather than a rhetorical one. Women were routinely excluded from clinical trials until the 1990s, drug doses were established in men and applied to women (zolpidem's dose was eventually halved for women after post-marketing data), heart attacks in women present differently and are diagnosed later, and women's pain is treated less promptly in emergency settings in multiple studies.

Where the numbers come from, and how much to trust them

In short: About half the world's deaths are never registered with a cause, so global health figures are models, and two reputable agencies routinely disagree.

Roughly half the deaths in the world are never registered with a certified cause. Civil registration and vital statistics systems are strong in high-income countries and weak or absent in much of Africa and South Asia, exactly where the disease burden is highest.

So global figures come from models. The Global Burden of Disease study, run by the Institute for Health Metrics and Evaluation with thousands of collaborators, combines surveys, censuses, hospital data, verbal autopsy (structured interviews with families about how someone died), and statistical modelling to estimate cause-specific mortality for every country. WHO produces its own estimates using overlapping data and different methods, and the two frequently disagree by meaningful margins.

Read the numbers in this book accordingly: as the best available estimates, accurate in direction and rank order, uncertain in the last digit, and sometimes revised substantially when methods change.

DALYs are worth understanding as a second measure. A disability-adjusted life year combines years of life lost to early death with years lived with disability, weighted by severity. It changes the ranking dramatically: low back pain, depression, migraine, hearing loss, and anxiety barely register in mortality tables and rank near the top in DALYs. A ranking by deaths tells you what to prevent; a ranking by DALYs tells you what people actually live with.

The forces changing the picture now

In short: Ageing, urbanisation, the double burden of malnutrition, climate, conflict, and antimicrobial resistance.

Ageing. The number of people over 60 is projected to roughly double by 2050, with most of that growth in low- and middle-income countries. Dementia, sensory loss, musculoskeletal disease, and multimorbidity follow, and the health systems that will face them are the ones least prepared.

Urbanisation. More than half the world lives in cities. This brings better access to services and worse air, more sedentary work, more processed food, and, in informal settlements, sanitation conditions resembling the nineteenth century alongside twenty-first century chronic disease.

The double burden. Many countries now face undernutrition and obesity simultaneously, sometimes in the same household: a stunted child and an obese parent. Early-life undernutrition followed by later calorie abundance appears to raise metabolic disease risk, which links the two directly.

Climate. Heat is already measurably increasing mortality, particularly among outdoor workers and older people. Mosquito-borne disease ranges are expanding to higher altitudes and latitudes. Crop yields, water security, and displacement all have downstream health effects. The chronic kidney disease epidemic among Central American agricultural workers (Chapter 23) is among the first clearly documented occupational disease epidemics attributable in part to heat.

Conflict and displacement. Over 100 million people are forcibly displaced. War destroys health systems, and the resulting excess deaths from disrupted vaccination, maternal care, and chronic disease treatment routinely exceed deaths from violence itself.

Antimicrobial resistance, discussed in Chapter 36, which is the main force capable of reversing twentieth-century gains.

The counterargument to pessimism

In short: Life expectancy up a decade since 1990, child deaths more than halved, and several diseases eliminated or made curable, none of it accidental and all of it reversible.

It is worth stating the positive case plainly, because health coverage is dominated by what is going wrong.

Since 1990: global life expectancy has risen by roughly a decade. Child deaths have more than halved. Maternal deaths have fallen by roughly a third. Smallpox is gone, polio is nearly gone, guinea worm has gone from 3.5 million cases a year to a handful, HIV has gone from a death sentence to a manageable condition, and hepatitis C has gone from incurable to curable in eight weeks. Deaths from malaria, tuberculosis, and diarrhoeal disease have all fallen substantially in absolute terms despite population growth.

None of this happened by itself. It came from vaccination programmes, oral rehydration, bed nets, antiretroviral scale-up, sanitation investment, tobacco control, road safety law, and the unglamorous work of health systems. It is reversible if funding and attention are withdrawn, which several recent trends in TB, malaria, HIV, and immunisation coverage demonstrate.

Sources and notes

Life expectancy (approximately 73 years globally), and the general framing of global health indicators, are from WHO's World health statistics 2025 and the WHO Global Health Observatory. Leading causes of death and their shares: WHO Global Health Estimates and Global Burden of Disease 2021 analyses; percentages vary between sources and years and are given as approximations. NCD share of deaths (roughly three-quarters): WHO NCD fact sheets. Under-5 mortality: UN Inter-agency Group for Child Mortality Estimation, most recent report (under 5 million deaths annually, down from about 20 million in 1950). Maternal mortality: WHO/UNICEF/UNFPA/World Bank Trends in maternal mortality, 2025 edition (approximately 260,000 deaths in 2023, ratio around 197 per 100,000 live births, about 70 percent in sub-Saharan Africa). Road traffic deaths: WHO Global status report on road safety. Suicide: WHO. Epidemiological transition: Omran, Milbank Memorial Fund Quarterly, 1971. McKeown thesis and its critiques: McKeown, The Role of Medicine, 1976, and Szreter's rebuttals. Whitehall studies: Marmot et al., from 1978 onward; see also Marmot, The Health Gap, 2015. US maternal mortality disparities: CDC National Center for Health Statistics. Death registration coverage: WHO civil registration and vital statistics assessments. DALY methodology: Global Burden of Disease study documentation.

Open questions. WHO and IHME estimates for the same quantity often differ, and neither should be treated as a count. How much of the social gradient in health is caused by material conditions versus psychosocial factors is genuinely contested. The health effects of climate change are projected with wide uncertainty ranges.

Next: why some diseases really do cluster in some ancestries, and why "race" is the wrong tool for thinking about it. 👉