At 37 degrees, the rate of admissions to intensive care after a cardiac arrest that occurred outside the hospital was more than double compared to days with temperatures around 29 degrees. An increase of 102%, recorded by a group of US researchers who analyzed over 11 thousand hospitalized patients between 2018 and 2024. Extreme heat, in addition to putting pressure on our bodies, can therefore also increase the workload of hospitals.
It is one of the results of five new studies released by the American Heart Association, in view of the scientific conferences scheduled in Chicago from 6 to 9 November 2026. Traffic noise, sleep times, energy drinks and cannabis consumption are also under observation. Very different factors, some linked to our habits, others to the environment in which we live. The studies are preliminary, but add new data to a line of research that looks well beyond traditional cardiovascular risk factors.
With extreme heat, hospitalizations for cardiac arrest increase
The research coordinated by Peter Graffy of the University of Chicago cross-referenced daily temperatures with intensive care unit admissions after out-of-hospital cardiac arrest in ten US health systems. Compared to days with maximum temperatures of around 29 degrees, the hospitalization rate increased by 45% when reaching 33 degrees and by 102% around 37. The association was particularly marked among the elderly and women.
Additionally, those who were hospitalized during warmer days were more likely to need treatments to support blood pressure and, subsequently, continuous dialysis for kidney problems. The heart has to work harder when the body tries to lose heat. In an already vulnerable person, this additional strain can aggravate a compromised cardiovascular situation.
The researchers also observed something unexpected: Among hospitalized patients, mortality and length of stay did not change significantly in relation to outdoor temperatures. The 102% figure therefore concerns hospitalizations, without directly measuring the individual risk of cardiac arrest.
For hospitals, meanwhile, the problem is real. A patient who survives a cardiac arrest may need intensive care for days or weeks, occupying beds and requiring specialized personnel. Graffy points out that the effects of heat waves continue even after the ambulance arrives at the hospital. And with increasingly frequent extreme temperatures, organizing health services becomes even more complicated.
Traffic noise weighs on the heart even when we sleep well
Living near a busy road means dealing with smog, of course. But there is also the noise of cars, buses, trains and planes. A background to which we can get used to, to the point of almost ceasing to notice. Our body, however, could continue to be affected. Research from Massachusetts General Hospital analyzed the health data of 108,051 adults collected between 2010 and 2020, comparing it with estimates of transportation noise in their respective areas of residence.
Exposure to average levels above 50 decibels over a 24-hour period was associated with an 8-10% increase in the development of cardiovascular risk factors, such as high cholesterol, hypertension and diabetes. The most exposed participants also had a greater likelihood of serious cardiac events. The researchers also verified the role of sleep, expecting that sleeping well could attenuate the association between noise and cardiovascular problems. The results showed a similar link between those who rested regularly and those who had sleep disorders.
Transport noise was therefore associated with cardiovascular problems even among those who slept well. A result that suggests potentially broader consequences than simply disturbed nights. And in Europe the dimensions of the phenomenon are anything but negligible.
According to the European Environment Agency’s report on environmental noise, prolonged exposure to transport noise contributes, according to epidemiological estimates, to around 49 thousand new cases of cardiovascular diseases every year in the European countries considered. Over 30% of the European population is exposed to transport noise levels above the World Health Organization recommendations. Millions of people who live daily with an environmental factor on which they can do very little.
Sleeping at different times is associated with greater cardiovascular risks
Six hours during the week, nine on the weekend, an early wake-up call, an evening shift. Catching up on sleep when possible may seem sufficient, but regular schedules also deserve attention. Research from Boston Children’s Hospital and Harvard Medical School analyzed over a million nights of sleep recorded through wearable devices by 10,362 adults participating in the US program All of Us.
After examining rest for about six months, the researchers followed the participants for a median period of 3.7 years. Changes in sleep schedules were associated with a 20-23% higher risk of serious cardiovascular events, including heart attack, stroke and heart failure.
Another finding concerns the duration of rest: each 29-minute increase in the variability of hours slept from one night to the next was associated with a 24% greater overall cardiovascular risk. The researchers also observed that a greater number of complete sleep cycles was associated with a 28% lower risk of atrial arrhythmias, while unusually long cycles were linked to a higher risk of heart attack and stroke.
Nguyen Minh Tuan Viet, a neuroscientist at Harvard Medical School, notes that sleep irregularity often depends on weekends or shift work. Keeping consistent hours could help cardiovascular health, although the observed associations do not prove a causal relationship. A seemingly simple piece of advice, especially for those who don’t have to organize their rest around shifts decided by others.
Energy drinks: eleven times more reports of cardiac arrest
Energy drinks are found on the shelves next to regular sodas. Colorful packaging, promises of concentration and a good dose of caffeine, often accompanied by other stimulating substances. Research from the University of Virginia examined 28,345 reports of possible adverse events submitted to the Food and Drug Administration between 2017 and 2025. Of those, 854 involved energy drinks or supplements containing caffeine and other stimulants.
In reports relating to these products, cardiac arrest appeared approximately eleven times more frequently than in reports relating to products without the same ingredients. Reports of heart attack were approximately 4.5 times more frequent. Nearly 45% of cardiovascular reports associated with stimulants were among people between 18 and 34 years old. The differences concern the frequency of reports, without directly representing the risk for each consumer.
According to the American Heart Association, some energy drinks can contain, at the same volume, up to three times the caffeine of filtered coffee, while some pre-workout supplements reach concentrations more than twelve times higher. Sai Samayamanthula, author of the study, notes that these products are marketed as normal daily stimulants. A placement that can lead to underestimating its effects, especially when combining different caffeine-containing products.
Cannabis and stroke, what emerges from the new data
Another research from Tulane University analyzed the telephone responses of 442,906 US adults collected between 2020 and 2024. Those who said they had consumed cannabis were more likely to report previous cardiovascular diseases, especially stroke. Among participants who had used cannabis one to five days in the previous month, the odds of reporting a previous stroke were 40 percent higher than in the group with no recent use, after statistical adjustments.
The authors suggest also considering cannabis use when assessing cardiovascular risk. The link observed in the questionnaires does not establish whether the substance directly contributed to the reported events. The topic acquires particular relevance in the United States, where in 2024 one in six adults declared having used cannabis in the last month, compared to one in ten in 2020.
The heart is also protected outside of hospitals
Already in January 2026, the American Heart Association, the European Society of Cardiology and two other scientific organizations published a joint statement on environmental risks to cardiovascular health, calling for stricter policies against air pollution, noise and extreme temperatures. The document estimates that all environmental factors contribute to 4-6 million cardiovascular deaths worldwide every year, about a fifth of the total.
Individual indications remain important: sleep enough, maintain a certain regularity, pay attention to stimulants. Alongside these recommendations, however, cardiologists also call for better designed cities, stricter limits on noise and healthcare facilities prepared to deal with the consequences of climate change. To reduce the noise of a street, moreover, it is not enough to send its inhabitants to bed earlier.
