VIENNA — Exposure to indoor air pollution may contribute to inflammation and autonomic nervous system dysfunction in patients with congestive heart failure who spend a lot of time inside, according to a real-world study.

The findings highlighted that pollutants such as nitrogen dioxide (NO₂) and fine particulate matter (PM_2.5), commonly generated by household activities, were associated with measurable changes in inflammatory markers and cardiac autonomic control.

The clinical implications may be important for patients with heart failure because they are often older, frail, and relatively sedentary. “Greater time spent indoors means that indoor air quality may have a disproportionate impact in this group,” said lead researcher and clinician Giacomo Mantineo, MD, Department of Cardiology, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy, presenting the data here at the 24th European Congress of Internal Medicine (ECIM) 2026.

Research Gap

Air pollution is already recognized as a major driver of cardiovascular disease. According to 2023 Global Burden of Disease study estimates, particulate matter pollution is among the leading contributors to disability-adjusted life years worldwide, second only to high systolic blood pressure. Previous studies have also linked short-term increases in air pollution to higher rates of hospitalization and mortality in patients with heart failure.

However, most research has focused on outdoor exposure, leaving a gap in understanding indoor environments where individuals may experience sustained and, at times, higher levels of pollutants.

“While outdoor air pollution has been extensively studied, indoor exposure remains underestimated, particularly in patients who are frail and spend most of their time at home,” said Mantineo. 

To address this, Mantineo and colleagues conducted a small, prospective, observational study that recruited 19 patients with heart failure from a cardiology unit in Milan. Participants were monitored in their home environments over a 7-day period to capture real-life exposure.

Indoor air quality was assessed continuously, focusing on NO₂ and PM_2.5 levels, while cardiac autonomic function was evaluated using 7-day ECG recordings. Blood samples were collected to measure inflammatory markers, including TNF alpha, interleukin 6 (IL-6), and triggering receptor expressed on myeloid cells 1 (TREM-1).

The study examined pollutant levels around the commonly cited thresholds of approximately 40 μg/m³ for NO₂ and 25 μg/m³ for PM_2.5. These thresholds were considered to provide contexts that were clinically relevant.

The researchers built on prior work in healthy individuals, where higher indoor pollution levels were associated with increased inflammation and changes in heart rate variability, including alterations in the cyclic variation of heart rate index (CVHRI), a marker linked to sympathovagal balance: the relative activity of the sympathetic and parasympathetic/vagal branches of the autonomic nervous system.

Clear Signals in Autonomic Function and Inflammation

In patients with heart failure, higher indoor NO₂ levels were significantly associated with changes in cardiac autonomic control. A 10% increase in NO₂ corresponded to a 0.86 events/h increase in CVHRI (95% CI, 0.15-1.58; P = .022), indicating altered autonomic regulation.

PM_2.5 also showed a clear relationship with systemic inflammation. A 10% increase in PM_2.5 was associated with a 17.18% rise in TNF alpha levels (P = .006), suggesting a proinflammatory effect of indoor particulate exposure.

Further analysis demonstrated that NO₂ exposure was associated with an increased expression of inflammatory genes. For every 10% increase in NO₂, IL-6 expression rose by 8.94% (P = .026), and TREM-1 expression increased by 6.60% (P = .025).

Taken together, the findings point to a consistent relationship between indoor air pollution, inflammatory activation, and disruption of cardiac autonomic balance.

A Modifiable Risk but Practical Limitations

Unlike many traditional cardiovascular risk factors, indoor air pollution represents a potentially modifiable exposure at the individual level. Interventions such as improving ventilation, reducing combustion sources, and monitoring indoor air quality could offer simple strategies to mitigate risk.

The findings also add to a growing body of evidence linking environmental exposures to autonomic dysfunction, a mechanism increasingly recognized as relevant in cardiovascular disease.

During the discussion, the researchers acknowledged that implementing mitigation strategies may not always be straightforward. In urban settings, such as the city of Milan, outdoor air pollution frequently exceeds recommended limits, complicating advice around ventilation.

However, they suggested that targeted strategies might be the best approach. “We would recommend ventilating homes at times when outdoor pollution is lower, such as early morning or late evening. It is also important to ventilate the kitchen, typically the most polluted room, especially after cooking,” remarked Mantineo.

The researcher cautioned that the study was small and exploratory but emphasized its strengths, including real-world monitoring and simultaneous assessment of environmental, physiologic, and inflammatory parameters.

Further research in larger cohorts will be needed to confirm these findings and to determine whether interventions targeting indoor air quality can improve clinical outcomes in heart failure.

Laura Horsfall, PhD, a researcher at University College London, London, England, who studies the impact of indoor biomass fuel exposure on respiratory and cardiovascular health, told Medscape News Europe that the findings add to the growing evidence that indoor air pollution not only affects lung health but can also affect the heart and lead to broader inflammation in the body. “Important sources of indoor emissions include cigarette smoking, cooking — especially with gas hobs, open fires, and wood-burning stoves — and burning candles or incense.”

Horsfall’s research has investigated indoor pollution on health. “We’ve also shown that burning solid fuels indoors for heating is associated with faster declines in lung function over time, highlighting the importance of reducing exposure in the home.”

But, she added, there are simple, low-cost steps that can be taken to improve indoor air quality. “Avoiding smoking indoors is one of the most effective actions. Using extractor fans that vent outside, briefly opening windows during cooking, and limiting unnecessary indoor burning of solid fuels for heating, candles, or incense can all help. Where possible, switching from gas to induction cooking can reduce exposure to nitrogen dioxide (NO₂), and portable HEPA [high-efficiency particulate air] cleaners can lower fine particle (PM_2.5) levels.”

She suggested using weather apps that provide air quality information to help people decide whether opening windows is beneficial.

Mantineo and Horsfall reported having no relevant financial relationships.