Population Health: Leading Causes of Death & Social Determinants
Who dies of what at each age, how lost years are counted, and why address shapes health
Leading causes of death in the United States
All ages combined. Heart disease is the leading cause of death in the US, followed by cancer and unintentional injury; stroke, chronic lower respiratory disease (mostly COPD), Alzheimer disease, and diabetes come next. COVID-19 briefly ranked third in 2020 and 2021 before falling down the list.
Age changes the ranking. Most deaths occur after 65, so older adults largely set the overall ranking (deaths at younger ages lift unintentional injury to #3), but each age band has its own leader.
| Age group | Leading cause | Next causes | Note |
|---|---|---|---|
| <1 year | Congenital anomalies | Preterm birth/low birth weight; sudden unexpected infant death; unintentional injury; maternal pregnancy complications | Safe sleep prevents many sudden infant deaths |
| 1–44 years | Unintentional injury | Suicide and homicide in adolescents and young adults; heart disease and cancer climb by the early 40s | Mechanism shifts with age |
| 45–64 years | Cancer | Heart disease; unintentional injury | Lung cancer is the top cancer killer in both sexes |
| ≥65 years | Heart disease | Cancer; stroke; chronic lower respiratory disease; Alzheimer disease | Falls lead injury deaths |
| All ages | Heart disease | Cancer; unintentional injury; stroke; chronic lower respiratory disease | Driven by deaths after 65 |
Infants, injury, and violence
Infancy. Sudden unexpected infant death groups SIDS with accidental suffocation or strangulation in bed. Its risk falls with safe sleep: supine on a firm, flat surface free of soft bedding, room-sharing without bed-sharing, and no smoke exposure.
Unintentional injury, age 1 to 44. The mechanism changes with age. Toddlers drown in pools and bathtubs; school-age children and teenagers die most often in motor vehicle crashes; young and middle-aged adults die most often of unintentional drug overdose (poisoning), now driven largely by illicit synthetic opioids such as fentanyl.
Suicide and homicide. In adolescents and young adults, these two causes fill the places immediately behind unintentional injury, with their order varying by age band and year. Firearms account for most homicides and about half of suicides.
Counted by mechanism rather than intent, firearm injuries have been the leading cause of death among US children and adolescents aged 1–19 since 2020, overtaking motor vehicle crashes.
Older adults. In adults 65 and older, falls are the leading cause of injury death.
Summary measures of population health
Life expectancy. Period life expectancy at birth is the average years a newborn would live if current age-specific death rates persisted for life. US women outlive men by about 5 years. US life expectancy fell in 2020–2021, driven by COVID-19 and drug overdoses, and has since rebounded.
Years of potential life lost (YPLL). YPLL sums, over every death before a reference age (commonly 75), the reference age minus the age at death. A death at 25 contributes 50 years; a death at 74 contributes 1. Because premature deaths weigh most, injuries, suicide, homicide, and perinatal conditions rank far higher by YPLL than by death counts.
Disability-adjusted life years (DALYs). One DALY is one lost year of healthy life. DALYs add years of life lost to premature death (YLL) to years lived with disability (YLD), each year of disability weighted from 0 (full health) to 1 (equivalent to death). A condition causing 5 years of premature death plus 10 years lived at a disability weight of 0.2 costs 5 + 2 = 7 DALYs. The WHO Global Burden of Disease study ranks conditions by DALYs.
Quality-adjusted life years (QALYs). QALYs multiply years lived by a utility weight (0 = death, 1 = perfect health), so 10 years at a utility of 0.5 equals 5 QALYs. Cost-effectiveness analysis compares interventions by the incremental cost-effectiveness ratio (ICER): the difference in cost divided by the difference in QALYs, reported as cost per QALY gained. Lower ratios are more cost-effective.
| Measure | What it counts | Direction | Main use |
|---|---|---|---|
| Life expectancy | Average years expected at current age-specific death rates | Higher = better | Comparing populations and trends |
| YPLL | Years lost before a reference age | Higher = worse | Highlighting premature deaths |
| DALY | YLL + YLD | Higher = worse | Ranking disease burden |
| QALY | Years lived × utility | Higher = better | Cost per QALY gained |
Social determinants of health and disparities
Five domains. Social determinants are the conditions in which people are born, live, learn, work, play, and age; they are estimated to influence outcomes more than clinical care does. Healthy People 2030 groups them into five domains:
- Economic stability: employment, poverty, food insecurity, housing instability
- Education access and quality: early childhood education, high-school graduation, language and literacy
- Health care access and quality: insurance, access to primary care, health literacy
- Neighborhood and built environment: housing quality, air and water quality, crime and violence, access to healthy food, walkability
- Social and community context: social cohesion, discrimination, incarceration, civic participation
Health disparities. These are preventable differences in disease burden or opportunity borne by socially disadvantaged groups; in the US they track race and ethnicity, income, rurality, and disability. Health follows a social gradient: each step down the income ladder carries higher mortality. Rural residents have higher death rates from the leading causes (heart disease, cancer, unintentional injury, chronic lower respiratory disease, stroke), with fewer clinicians and longer travel.
Structural barriers. Many disparities are rooted in structures rather than individual choices: residential segregation shaped by historical redlining, which concentrated poverty and pollution; cost and insurance gaps; lack of transportation; inflexible work hours; and language barriers. Durable fixes need policy-level change, not only individual counseling.
Equity, health literacy, and the epidemiologic transition
Equity versus equality. Equality gives everyone the same resources. Equity distributes resources according to need so that everyone can reach their full health potential; free transportation offered to patients who lack it is equity in action. Differences that are avoidable, unjust, and rooted in social disadvantage are called health inequities.
Health literacy. Health literacy is the capacity to find, understand, and use health information to make decisions. Limited health literacy is common, often hidden, and linked to more hospitalizations, lower use of preventive care, and medication errors. Use plain language, a few key points, and visual aids; confirm understanding with teach-back (the patient restates the plan in their own words); and use trained medical interpreters, not family members, for limited English proficiency.
Apply universal precautions for health literacy: assume any patient may have difficulty understanding, regardless of appearance, education, or fluent conversation.
Epidemiologic transition. As societies develop, improvements in sanitation, nutrition, vaccination, and antibiotics sharply reduce infectious and childhood deaths. Life expectancy rises, the population ages, and chronic noncommunicable diseases (cardiovascular disease, cancer, diabetes, chronic lung disease) become the dominant causes of death. The classic model runs from an age of pestilence and famine, through receding pandemics, to an age of degenerative and human-made diseases. Many low- and middle-income countries now carry a double burden of persisting infections alongside rising chronic disease.