Heat-health risks hit vulnerable seniors at temperatures well below official warning thresholds

Every major city has a heat threshold - a temperature at which officials activate emergency protocols, open cooling centers, and push public warnings. In New York City, that line sits at a heat index of 95 degrees Fahrenheit sustained over two days. The assumption is that below that mark, heat is uncomfortable but manageable.

For socioeconomically vulnerable older adults, that assumption appears to be wrong.

A growing crisis measured in ER visits

Heat-related mortality in the United States has been climbing at an alarming rate - roughly 17% per year since 2016. Older adults bear a disproportionate share of this burden. They are more likely to have chronic conditions that impair thermoregulation, more likely to take medications that interfere with sweating, and more likely to live in housing that traps heat.

But the municipal warning systems designed to protect them are calibrated using population-wide data. They capture the temperature at which deaths increase across an entire city, not the temperature at which a particular community begins to suffer. The distinction matters because heat vulnerability is not evenly distributed.

A study published March 20 in JAMA Network Open examined this gap directly. Researchers at NYU Grossman School of Medicine analyzed emergency department visits by patients aged 65 and older at a hospital serving a socioeconomically vulnerable population in New York City. The patient base was racially and ethnically diverse, with a Medicaid enrollment rate twice that of a comparison hospital ten miles away.

90 degrees, not 95

The findings were striking. At the emergency department serving the more vulnerable population, heat-associated visits began increasing at a daily heat index maximum of just 66 degrees Fahrenheit. Risks amplified sharply between 90 and 101 degrees.

That 90-degree amplification point falls five degrees below New York City's official heat advisory threshold. On days when the heat index reaches 90 but stays below 95, the city does not activate its emergency heat protocols. No cooling centers open. No special advisories are issued. Yet older adults in underserved communities are already arriving at emergency departments in elevated numbers.

At a comparison emergency department serving a higher-income, predominantly white, privately insured population, no significant association between heat index and ED visits in older adults was observed. The divergence between the two sites underscores that heat risk is shaped as much by social and economic conditions as by temperature alone.

What drives the disparity

The factors that make heat more dangerous for low-income older adults are well documented. They include housing without adequate air conditioning, neighborhoods with more pavement and less tree canopy, limited access to transportation to cooling centers, and higher prevalence of heat-sensitive conditions such as cardiovascular disease, kidney disease, and diabetes.

Medications commonly prescribed to older adults - including diuretics, beta-blockers, and anticholinergics - can also impair the body's ability to cool itself. An older person taking a diuretic for heart failure who lives in a top-floor apartment without air conditioning faces a fundamentally different heat risk than a similarly aged person with central air conditioning and a car to drive to a cooled environment.

The study's lead author, Alexander Azan, assistant professor in the Department of Population Health at NYU Langone, emphasized that electronic health record data offered an opportunity to identify heat exposure thresholds specific to vulnerable populations - thresholds that differ from the population-level trends informing municipal warning systems.

Using hospital data to build better warnings

The study's most practical implication is not just that the 95-degree threshold is too high for some populations. It is that healthcare systems already possess the data to identify their own thresholds.

Electronic health records contain detailed information about patient visits, diagnoses, demographics, and insurance status. Matched against publicly available weather data, these records can reveal the specific temperature ranges at which a hospital's patient population begins to experience heat-related health crises. Each hospital, each community, could have its own evidence-based trigger point.

Co-investigator Leora I. Horwitz, director of the Center for Healthcare Innovation and Delivery Science at NYU Langone, highlighted the potential for healthcare system-based heat warning strategies. Rather than waiting for a city-wide advisory, hospitals could proactively contact vulnerable patients, activate outreach programs, or coordinate with community organizations when local data suggest heat risks are rising.

The research team estimated that a system-based warning triggered at 90 degrees on days without a municipal advisory could have prevented approximately 116 ED visits at the community hospital over the three-year study period.

Constraints of the current evidence

The study examined only two emergency departments within one health system in one city. New York City's climate, demographics, and urban infrastructure are not representative of all U.S. cities. The specific temperature thresholds identified - 66 degrees for initial risk, 90 degrees for amplified risk - may not apply to communities in different climatic zones with different housing stock and demographic profiles.

The analysis is observational and cannot establish that heat directly caused the increase in ED visits. Other factors correlated with hot weather - air quality, changes in behavior, dehydration from outdoor activity - could contribute to the observed associations.

Temperature data came from a single monitoring station at LaGuardia Airport, which may not capture the microclimate variations within neighborhoods. Urban heat islands can produce temperature differences of several degrees within a single borough, meaning that some patients may have experienced heat exposure significantly above or below the recorded value.

The study also cannot capture heat-related illness that does not result in an emergency department visit. Older adults who suffer heat exhaustion at home but do not seek care, or who are cared for by family members or at urgent care clinics, are invisible in this dataset. The true burden of heat on vulnerable seniors is likely larger than what ED data alone can show.

From population averages to community realities

The broader lesson extends beyond New York City. Municipal heat warning systems were designed to reduce heat-related deaths across an entire metropolitan area. They accomplish that goal imperfectly, because the populations within a city are not homogeneous. The temperature that is merely uncomfortable for a healthy adult with air conditioning can be medically dangerous for an elderly person with heart failure in a poorly ventilated apartment.

The research team plans next to examine how social and structural risk factors further modify heat-associated ED risks, and to determine which specific health conditions in older adults are most sensitive to heat exposure. Their goal is a framework that allows healthcare systems to deploy targeted interventions - not just alerts, but actions - before patients arrive at the emergency department.

The gap between 90 and 95 degrees is small on a thermometer. In clinical terms, for the most vulnerable patients, it may represent the difference between a proactive warning and a preventable crisis.