Life expectancy is shaped by a long list of factors, from personal habits like smoking and diet to structural forces like poverty and air quality that no individual fully controls. Some of these shave off a few months; others cost a decade or more. What makes the picture complicated is that many of these risks overlap and amplify each other, so a person dealing with low income, poor sleep, and chronic stress simultaneously faces a burden far greater than any single factor would predict. The research, though, is clear enough on which factors matter most and roughly how much each one costs.
Smoking and Alcohol
Tobacco remains the single largest behavioral killer in most high-income countries. A long-running Dutch cohort study found that average cigarette smoking reduced total life expectancy by about 7 years, while heavy smoking cut nearly 9 years off.1PubMed Central. Mortality and life expectancy in relation to long-term cigarette, cigar and pipe smoking: the Zutphen Study A global analysis covering dozens of countries estimated that tobacco-related deaths account for roughly 20% of all adult mortality, with the toll heavier in men than women.2BMJ Journals. The impact of cigarette smoking on life expectancy between 1980 and 2010: a global perspective These figures reflect population averages. For any individual smoker, the damage depends on how many cigarettes per day, how many years, and how early they started.
Alcohol tells a similarly grim story for heavy drinkers. People with alcohol use disorder die at roughly three and a half times the rate of the general population, and the risk is even steeper for women with alcohol use disorder, whose mortality rates run more than four and a half times higher than their peers.3PubMed Central. Alcohol and life expectancy One population-based cohort study found that regular male drinkers lost about 7 years of life expectancy compared with nondrinkers, and when smoking was added on top, the combined loss exceeded 10 years.4Scientific Reports. The effects of modest drinking on life expectancy and mortality risks: a population-based cohort study That stacking effect is worth noting: smoking and drinking together do more harm than either one alone, and a large share of people who drink heavily also smoke.
Diet and Body Weight
What you eat matters independently of whether you smoke or drink. A growing body of research has focused on ultra-processed foods, the category that includes packaged snacks, sugary drinks, instant noodles, and many ready-to-eat meals. An umbrella review pooling dozens of epidemiological meta-analyses found that high ultra-processed food consumption was associated with about a 21% increase in all-cause mortality risk.5BMJ. Ultra-processed food exposure and adverse health outcomes: umbrella review of epidemiological meta-analyses An updated dose-response meta-analysis put the figure somewhat lower, at about a 15% increased risk when comparing the highest consumers to the lowest, with each additional 10% of calories from ultra-processed foods linked to roughly a 10% higher mortality risk.6PubMed Central. Ultra-processed foods and risk of all-cause mortality: an updated systematic review and dose-response meta-analysis of prospective cohort studies A large U.S. cohort study found a more modest association, with participants in the highest quarter of ultra-processed food intake showing about a 4% higher all-cause mortality rate, driven mainly by deaths from causes other than cancer or heart disease.7PubMed Central. Association of ultra-processed food consumption with all cause and cause specific mortality: population based cohort study The range across studies is wide, but the direction is consistent: more ultra-processed food, higher mortality.
Excess body weight is closely tied to diet and carries its own independent toll. A U.K. cohort of 3.6 million adults found that obesity overall shortened life expectancy from age 40 by about 4 years in men and 3.5 years in women compared with healthy-weight individuals, while the most severe obesity (class 3) cost about 9 years in men and nearly 8 in women.8The Lancet. Association of BMI with overall and cause-specific mortality: a population-based cohort study of 3·6 million adults in the UK Age matters here enormously. An earlier analysis estimated that severely obese young white men in their twenties could lose up to 13 years of life expectancy, a potential 22% reduction in remaining lifespan, while the same degree of obesity in adults over 60 had a much smaller effect.9JAMA. Years of Life Lost Due to Obesity In other words, carrying excess weight when you are young is far more damaging to long-term survival than developing it later in life.
Physical Inactivity and Sleep
A sedentary lifestyle raises the risk of death from cardiovascular disease, cancer, and metabolic conditions like diabetes.10PubMed Central. Sedentary Lifestyle: Overview of Updated Evidence of Potential Health Risks Even the specific kind of sitting matters. A large study found that people who mostly sit at work face about a 16% higher all-cause mortality risk and a 34% higher cardiovascular mortality risk compared with those whose jobs keep them on their feet.11JAMA Network Open. Occupational Sitting Time, Leisure Physical Activity, and All-Cause and Cardiovascular Disease Mortality Critically, it is the combination that matters most. People with both low physical activity and high sitting time had about a 47% higher mortality risk compared with the most active and least sedentary group.12PubMed. A Physical Activity and Sitting Time Balance Index and All-Cause Mortality Risk
Sleep has emerged as another predictor that rivals some of the more familiar risk factors. A meta-analysis of prospective studies found that habitually short sleep was linked to about a 12% increased risk of death.13PubMed Central. Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies A state-and-county-level analysis in the U.S. found that sleep insufficiency correlated with lower life expectancy more strongly than almost any other health behavior measured, second only to smoking.14SLEEP Advances. Sleep insufficiency and life expectancy at the state-county level in the United States, 2019–2025 Night shift work adds to this burden: frequent night shift workers lost roughly a year of life expectancy at age 45 compared with daytime workers.15QJM: An International Journal of Medicine. Night shift work, accelerated biological aging and reduced life expectancy: a prospective cohort study A separate study found that working night shifts for more than five years raised overall mortality risk by about 15%.16PubMed Central. Night work, mortality, and the link to occupational group and sex
Air Pollution and Environmental Toxins
The air you breathe can quietly take years off your life. A worldwide analysis estimated that ambient air pollution causes about 8.8 million excess deaths per year globally and reduces life expectancy by an average of 2.9 years, making it a larger contributor to mortality than tobacco smoking at the population level.17PubMed Central. Loss of life expectancy from air pollution compared to other risk factors: a worldwide perspective That global average obscures a huge range. In countries with severe pollution, the loss is much larger; in places with cleaner air, it is smaller. In the United States, a landmark study showed that a decrease of 10 micrograms per cubic meter in fine particulate matter (PM2.5) was associated with roughly a 0.6-year gain in life expectancy, and reductions in air pollution accounted for as much as 15% of the overall improvement in U.S. life expectancy during the study period.18PubMed Central. Fine-particulate air pollution and life expectancy in the United States
Chemical contaminants in the environment also register as mortality risks. Low-level lead exposure, the kind common in many older U.S. homes and water systems, was linked to about an 18% population-attributable fraction of all adult deaths in one major analysis, an estimated 412,000 deaths per year.19PubMed. Low-level lead exposure and mortality in US adults: a population-based cohort study A systematic review and meta-analysis confirmed that arsenic, lead, and cadmium exposure are each independently associated with higher cardiovascular disease risk, with lead showing the strongest links to both coronary heart disease and stroke.20BMJ. Environmental toxic metal contaminants and risk of cardiovascular disease: systematic review and meta-analysis These are not exotic industrial exposures. Most people encounter trace amounts of these metals through drinking water, food, soil, and aging infrastructure.
Income, Education, and Access to Healthcare
Socioeconomic position is one of the strongest predictors of how long a person lives. A landmark U.S. study found that the gap in life expectancy between the richest 1% and the poorest 1% was about 15 years for men and 10 years for women, and that gap widened between 2001 and 2014.21PubMed Central. The Association Between Income and Life Expectancy in the United States, 2001–2014 A more recent cohort study of predominantly low-income Americans found that people earning less than $15,000 per year had over three times the mortality rate and more than 10 years shorter life expectancy compared with those earning $50,000 or more.22PubMed Central. Impacts of Poverty and Lifestyles on Mortality: A Cohort Study in Predominantly Low-Income Americans
Education may be even more powerful than income in some settings. A global meta-analysis found that each year of schooling reduced mortality risk by about 2%, and completing secondary school was associated with a roughly 25% lower risk of death compared with having no education at all.23The Lancet Public Health. Education and all-cause mortality: a systematic review and global meta-analysis In India, education predicted mid-age mortality more strongly than wealth, with the decline in death risk across the education spectrum exceeding the decline across wealth categories by a wide margin.24PubMed Central. For reducing premature adult mortality in India, education matters more than income In China, people with less than a primary education had nearly double the premature mortality risk of those who completed upper secondary school, with particularly large gaps for respiratory disease and other non-cancer causes.25PubMed Central. The association between education and premature mortality in the Chinese population: a 10-year cohort study
Lack of health insurance sits alongside these structural factors. A review of the evidence concluded that being insured reduces the odds of dying by somewhere between 3% and 29%, supporting the straightforward conclusion that health insurance saves lives.26PubMed. The Relationship of Health Insurance and Mortality: Is Lack of Insurance Deadly? A national cohort study found that unemployment, food insecurity, low education, and lacking private health insurance were all independently associated with premature death after controlling for the other factors, meaning none of them is simply a proxy for the others.27PubMed Central. Social determinants of health and premature death among adults in the USA from 1999 to 2018: a national cohort study
Mental Health and Social Isolation
Severe mental illness is among the most underappreciated drivers of early death. People with conditions like schizophrenia, major depression, and bipolar disorder die 10 to 25 years sooner than the general population.28PubMed Central. Mortality gap and physical comorbidity of people with severe mental disorders: the public health scandal Most of that gap comes not from suicide but from preventable physical illness: heart disease, diabetes, respiratory disease, and infections that go undertreated. An Australian population study found that the life-expectancy gap for people with any mental disorder actually grew over two decades, reaching nearly 16 years for men and 12 years for women by 2005.29PubMed Central. The gap in life expectancy from preventable physical illness in psychiatric patients in Western Australia: retrospective analysis of population based registers That the gap is widening, not narrowing, suggests that mental-health care improvements have not kept pace with gains in physical health care.
Loneliness and social isolation, while distinct from clinical mental illness, carry their own mortality penalties. A meta-analysis found that social isolation raised the risk of early death by about 29%, loneliness by 26%, and living alone by 32%, even after adjusting for confounders like age, sex, and health status.30PubMed. Loneliness and social isolation as risk factors for mortality: a meta-analytic review A more recent systematic review and meta-analysis of cohort studies arrived at a similar figure, estimating that socially isolated people had about a 33% higher all-cause mortality risk.31PubMed Central. Social isolation as a risk factor for all-cause mortality: Systematic review and meta-analysis of cohort studies These effect sizes are comparable to well-established risk factors like light smoking or physical inactivity.
How Much Does Genetics Actually Matter
Genes unquestionably play a role in lifespan, but their influence is smaller than most people assume. A multi-cohort study using polygenic risk scores found that people genetically predisposed to a short lifespan had about a 21% higher death rate than those predisposed to a long lifespan. In comparison, people with an unfavorable lifestyle had a 78% higher death rate than those with a favorable lifestyle.32BMJ Evidence-Based Medicine. Genetic predisposition, modifiable lifestyles, and their joint effects on human lifespan: evidence from multiple cohort studies The combined penalty was roughly doubled for people who had both bad genes and bad habits, but the crucial finding was that no multiplicative interaction was detected. This means healthy behaviors offset genetic risk rather than being overwhelmed by it.
A study of older Chinese adults put concrete numbers on the offset: shifting from an unhealthy to a healthy lifestyle was associated with roughly 4 additional years of life expectancy at age 65, and the gain was essentially the same regardless of whether a person’s genetic risk was low or high.33The Lancet Healthy Longevity. Association of healthy lifestyle and genetic risk with mortality and life expectancy among older Chinese adults: a nationwide prospective cohort study The practical implication is encouraging: you cannot choose your genes, but lifestyle choices appear to matter far more than your genetic hand, and healthy habits help about as much for people dealt a poor genetic hand as for those dealt a good one.
Violence, Drugs, and Chronic Disease Overlap
Some factors hit specific demographic groups especially hard. The opioid crisis in the United States reduced national life expectancy by about 0.67 years in 2022, up from 0.52 years in 2019, with the burden falling increasingly on Black, Hispanic, and Native American communities.34PubMed Central. Impact of opioid overdoses on US life expectancy and years of life lost, by demographic group and stimulant co-involvement: a mortality data analysis from 2019 to 2022 A separate analysis found that drug and firearm deaths combined reduced male life expectancy in the U.S. by 1.67 years in 2020, tripling from 0.67 years two decades earlier.35PubMed. The effect of drugs and guns on life expectancy in the United States, 2000-2020 Violence has an outsized effect on young men in particular. In Venezuela, homicide alone shaved about 1.5 years off male life expectancy, with nearly all losses concentrated in men between 15 and 50.36International Journal of Epidemiology. The impact of violence on Venezuelan life expectancy and lifespan inequality
Chronic diseases like diabetes and hypertension, meanwhile, erode life expectancy through a slower but relentless process. Having type 2 diabetes with uncontrolled blood pressure dramatically worsens cardiovascular outcomes, and the association between elevated blood pressure and death is strongest in younger diabetic patients.37PubMed Central. Age-specific associations between blood pressure and cardiovascular disease, kidney disease, and death among individuals with type 2 diabetes: a population-based cohort study These conditions rarely exist in isolation. A person with diabetes is more likely to be overweight, sedentary, and dealing with high blood pressure simultaneously, and each additional condition multiplies the others’ effects on survival.
Temperature Extremes and Catastrophic Events
Both hot and cold temperatures kill, though in different patterns. A large multicountry study found that about 7.7% of all deaths during the study period could be attributed to non-optimal temperatures. Cold was far more deadly than heat, responsible for about 7.3% of deaths compared with heat’s 0.4%.38PubMed Central. Mortality risk attributable to high and low ambient temperature: a multicountry observational study That cold-dominance surprises many people, since heat waves get more news coverage. But chronic exposure to moderately cold days accumulates a much larger body count than the occasional extreme heat event. A 2025 cohort study of over 9 million people confirmed that extreme high temperatures do raise mortality in a linear dose-response pattern, with each unit increase in extreme heat days, frequency, and severity independently linked to higher death rates.39PubMed Central. Association between long-term extreme high temperature and mortality: a 9-million prospective cohort study As global temperatures rise, the balance between cold and heat deaths is expected to shift.
On a larger scale, pandemics and wars have historically caused sudden, dramatic drops in life expectancy. The 1918 influenza pandemic reduced life expectancy in the United States by nearly 12 years, and the 2014 Ebola outbreak cut life expectancy in Liberia by roughly 2 to 6 years.40PubMed Central. Effect of COVID-19 Epidemic on Life Expectancy and Years of Life Lost in Iran: A Secondary Data Analysis Historical analysis of European catastrophic events across two centuries confirms a consistent pattern: pandemics and wars cause sharp drops in life expectancy, followed by recoveries whose speed and completeness vary by age and sex.41Canadian Studies in Population. Life Expectancy Loss and Recovery by Age and Sex Following Catastrophic Events in Europe during the 19th and 20th Centuries These events are reminders that life expectancy is not a one-way escalator. Progress can reverse quickly under the right conditions, and the gains of decades can be erased in a few years.