Heat, Poor Air Quality Ups Heart Attack Risk

Medscape

18-06-2025

Simultaneous exposure to ozone pollution and high temperatures significantly increases the risk for acute myocardial infarction (MI) among adults in the US, according to a recent study published in Circulation .
The findings highlight the dangers of joint environmental stressors even at moderate levels and the importance of timely patient counseling.
Using nationwide private insurance claims data from 2016 to 2020, researchers from Yale School of Public Health, New Haven, Connecticut, and collaborators identified 270,123 cases of acute MI in people aged 18-64 years. They found joint exposure to ground-level ozone (60 ppb) and high temperatures — roughly 90-95 °F — increased the risk for an MI by 33% compared to cooler, low-ozone days. Even under moderate conditions, such as an ozone count of 50 ppb and typical temperatures around 70 °F, the risk increased by 15%.
'The lag 0f effect means clinicians need to pay close attention to high-pollution and hot days in real time,' said Lingzhi Chu, PhD, a postdoctoral associate in the Department of Environmental Health Sciences at the Yale School of Public Health and colead author of the study 'Clinicians should emphasize to younger patients that moderate levels still pose risks' to cardiovascular health.
Mary Johnson, PhD, a principal research scientist of environmental health at the Harvard T.H. Chan School of Public Health in Boston, said the findings bring much-needed attention to a younger demographic.
'This study is important because it focuses on a younger age group that is often overlooked in cardiovascular research,' said Johnson, who was not involved in the study. 'Typically, you don't think about heart attacks happening in people in the young adult category.'
Johnson also noted the value of examining heat and ozone together.
'We've seen studies showing impacts from temperature and from ozone individually,' she said, 'but looking at them together, and especially looking at differences between men and women, is important.'
Different Risks by Sex
According to the study, women showed increased vulnerability on days with both high ozone and temperatures around 90-95 degrees, while men experienced heightened risk even when only one factor was elevated. The difference in exposure-response patterns by sex was statistically significant ( P = .016).
Chu said clinicians should tailor counseling based on patient demographics.
'The sex difference that males are vulnerable to mild exposures is critical,' Chu said. 'Young men need targeted proactive counselling.'
While the researchers did not assess comorbidities like hypertension or diabetes, Chu acknowledged these conditions could affect risk.
'The potential pathophysiology suggests hypertension, diabetes, or obesity may compound risks, but further research is warranted,' Chu said.
Johnson said these findings should challenge assumptions in primary care because these clinicians often are the first to encounter patients of the age group studied.
'Just because you're young and healthy does not necessarily rule out the risk of a cardiac event,' she said. 'Especially if there's a combination of poor air quality and elevated temperature.'
Communicating Practical Prevention
Acute MI is a leading cause of morbidity and mortality globally, with approximately 800,000 cases annually in the US. Adults younger than 55 years, and particularly women, account for a growing share of acute MIs.
Chu recommended several practical prevention strategies clinicians can share with patients: Adjusting the timing of outdoor activities, staying hydrated, and using cooling methods such as fans or air conditioning.
She also acknowledged the challenge clinicians face in educating patients without overwhelming them.
'Clinicians may consider framing mitigation as simple behavior changes rather than drastic life changes to prevent patient overwhelm,' she said. 'Some of these simple changes — like checking air quality apps, closing windows on high-ozone days, or staying hydrated — support overall health, not just cardiovascular health.'
Johnson agreed.
'While we can't individually control wildfires or ozone formation, everyone can be aware of ozone levels and temperature before going outside or doing anything physically strenuous,' she said.
Health Equity Concern
The study relied on data from individuals with private insurance, a limitation both Chu and Johnson acknowledged.
'That population has access to care,' Johnson said. 'But what about the uninsured or underinsured? They may be more at risk because they often live in areas with worse air quality and lack resources to adapt, like access to cooling systems or healthcare.'
She added that events like sudden cardiac death may be underreported in uninsured populations.
'They don't go to the emergency room. They die before they get there,' Johnson said. 'So the real risk may actually be higher than what this study captured.'
Johnson said the findings also highlight a critical shift in how clinicians should view environmental risk.
'It's accurate to say we can no longer think about air pollution and environmental risks as being linked only to chronic conditions,' said Johnson. 'There are acute consequences, too, and this study illustrates that clearly.'
A study published last month in the journal Epidemiology found prolonged exposure to the particulate matter in wildfire smoke was associated with small increases in the risk for several cardiovascular diseases, especially hypertension.
As climate change drives more frequent heat waves and worsens air quality, both Chu and Johnson said clinicians are on the front lines of patient education and prevention.
'Clinicians are key players in translating environmental health research into actionable prevention,' Chu said. 'This study reinforces the need to think beyond traditional risk factors.'
Chu and Johnson reported no relevant financial conflicts of interest.