Heat waves and annual death rates in older adults in the United States
A new nationwide study of more than 73 million older Americans finds that heat waves are driving a substantial increase in deaths each year, with disproportionate impacts on Black and low‑income communities, while neighborhoods with more green space see lower death rates.
Published in The Lancet Planetary Health, a new paper by Harvard Chan School Researchers including Harvard Chan C-CHANGE director Mary Rice and core faculty member Joel Schwartz, examines how heat waves affect annual mortality among Americans aged 65 and older. While previous research has focused on deaths in the days immediately following extreme heat, this work examines mortality over an entire year, capturing the delayed health effects after a heat wave.
The research team analyzed Medicare records from over 73.7 million beneficiaries living in nearly 28,000 ZIP codes across the contiguous United States between 2000 and 2018. They then combined these data with temperature records to identify heat waves at the neighborhood level, with “heat wave” defined as at least two consecutive summer nights when the minimum temperature was unusually high for that location.
Their findings suggest that climate‑driven increases in the number of heat waves pose a major and growing threat to public health in the United States, especially for older adults in Black communities and residents of high‑poverty neighborhoods, while investments in creating more green space could provide meaningful protection.
The study also provided insights into the ways in which Americans die from heat waves, with mortality from heart attacks, Alzheimer’s disease complications, pneumonia and COPD being of note.
Key Takeaways
Heat waves increase annual deaths among older adults.
- For older adults, heat waves led to about 9 extra deaths per heat wave per 10,000 people each year. Across the contiguous U.S. from 2000–2018, this added up to about 17,600 extra deaths among older adults.
- In a hypothetical scenario where climate change caused every ZIP code in the study to have one additional heat wave per decade, the researchers estimated it would lead to about 56,800 additional premature deaths among older adults.
- Increased heat waves were associated with cardiovascular, respiratory, and neurological deaths.
The mortality burden of heat waves falls disproportionately on Black communities.
- The increase in annual mortality associated with heat waves was nearly three times higher for Black individuals than for white individuals.
- For Black individuals, each additional heat wave was associated with 16.50 extra deaths per 10,000 people each year, compared with 5.85 extra deaths per 10,000 people for white individuals.
- This higher burden for Black communities reflects a history of redlining and disinvestment, which has led to disproportionately higher temperatures in these neighborhoods, as well as less access to medical care and higher rates of diabetes.
There are higher risks in high‑poverty neighborhoods.
- Older adults living in the 25% of ZIP codes with the most poverty experienced a significantly stronger link between heat waves and mortality, with about 11 extra deaths per 10,000 people per year per heat wave.
- Low‑income communities often face compounding vulnerabilities, including fewer cooling resources, reduced access to healthcare, and hotter neighborhood conditions due to the urban heat island effect.
Green space appears protective.
- In ZIP codes with the highest levels of green space, heat waves were associated with a reduction in annual mortality, with 13.51 fewer deaths per 10,000 people per year per heat wave.
- These findings support the role of trees, parks, and other vegetation in cooling neighborhoods and protecting health, and point to urban greening as a promising adaptation strategy.
Authors
- James P Healy MPH, Harvard T H Chan School of Public Health
- Edgar Castro PhD, Harvard T H Chan School of Public Health
- Mahdieh Danesh Yazdi PhD, Harvard T H Chan School of Public Health, Stony Brook University School of Medicine
- Mary B Rice MD, Center for Climate, Health, and the Global Environment, Harvard T H Chan School of Public Health
- Howard Chang PhD, Emory Rollins School of Public Health
- Joel Schwartz, PhD Department of Environmental Health, Harvard TH Chan School of Public Health
