New Haven, Conn. — A sweeping new study led by researchers at the Yale School of Public Health (YSPH) reveals stark disparities in life expectancy across U.S. states and Washington, D.C. over the past century – offering new insights into how a region’s public health policies, social conditions, and environmental factors can shape people’s lifespans.

Analyzing more than 179 million deaths between 1969 and 2020, the multi-institutional research team traced life expectancy trends by birth cohort — a more precise measure for following the life experiences of a population than traditional year-by-year summaries of mortality, which represent a mix of many generations.

The study, which appears in JAMA Network Open, found that some states saw dramatic gains in life expectancy, while others, particularly in the U.S. South, experienced little or no improvement over an entire century.

“For females born in some Southern states, life expectancy increased by less than three years from 1900 to 2000,” said Theodore R. Holford, the Susan Dwight Bliss Professor Emeritus of Biostatistics at YSPH and lead author of the study. “That’s a staggering contrast when you consider that in states like New York and California, life expectancy rose by more than 20 years over the same period.”

States in the Northeast and West, along with the District of Columbia, recorded the greatest gains. Notably, the nation’s capital had the lowest life expectancy for the 1900 birth cohort but improved by 30 years for females and 38 years for males by 2000.

By contrast, states like Mississippi, Alabama, and Kentucky saw minimal gains, particularly among women, suggesting that systemic factors — like socioeconomic disadvantages, limited access to health care, and weaker public health initiatives — have lasting impacts on mortality, researchers say.

“These trends in mortality and life expectancy reflect not only each state’s policy environment but also their underlying demographics as well,” said Jamie Tam, an assistant professor of health policy and management at YSPH and co-author of the study. “It’s not surprising that states with fewer improvements to life expectancy also have higher rates of poverty for example.”

The researchers used an age-period-cohort model, allowing them to disentangle the effects of aging, historical events, and generational influences on mortality. This method captured how early-life exposures — such as access to sanitation, vaccinations, or tobacco — shaped health trajectories later in life.

“Looking at mortality trends by cohort gives us a more accurate reflection of the lived experiences of populations,” Holford said. “It shows the long-term impact of policies and social conditions affecting the life course of populations that might otherwise be invisible in year-by-year comparisons of mortality rates from different generations.”

The team also examined the rate at which mortality increased after age 35, which is summarized by the number of years it takes for an individual’s risk of death to double. Longer doubling times indicate healthier aging. Again, researchers observed stark differences between states: New York and Florida showed slower mortality increases, while Oklahoma and Iowa saw faster mortality escalations.

Holford emphasized that these patterns aren’t just a reflection of the past. “The disparities we see today are the result of decades of cumulative effects — on smoking rates, health care access, environmental exposures, and public health investments,” he said. “Without conscious policy changes, these gaps will likely persist or even widen.”

The researchers pointed to California and Kentucky as examples of how local health policies can influence mortality rates. California was an early adopter of smoke-free workplace policies in 1995, which led to entire generations of young people growing up in smoke-free environments, as well as generations of working-age adults who were prompted to quit, the research said.

In contrast, Kentucky essentially made no effort to control cigarette smoking, resulting in higher cigarette use and, therefore, higher mortality compared with California. Similar patterns for smoking and higher mortality were observed in West Virginia, Oklahoma, Arkansas, Tennessee, Louisiana, Mississippi, and Alabama, the study said. Lower socioeconomic status is also associated with higher mortality risk; states that are socioeconomically advantaged appeared to have improved mortality rates more quickly than other states, according to the study.

The researchers hope their findings encourage greater focus on interventions — like tobacco control, health care access, and environmental protections — that can transform life expectancy outcomes for future generations.

“This research highlights the importance of viewing health through a generational lens,” Tam said. “The benefits of health interventions ripple across lifetimes.”

As Holford put it, “Where you are born shouldn’t determine how long you live. But in America, it still does.”