A recent cross-institutional study, partially funded by the National Institutes of Health, has revealed that exposure to dry air can significantly increase the risk of dehydration and inflammation in human airways. This condition, which is expected to worsen with global warming, is closely associated with respiratory issues such as asthma, allergic rhinitis, and chronic cough.
Researchers found that as the Earth’s climate warms and relative humidity remains relatively constant, a phenomenon known as vapor pressure deficit (VPD) rises rapidly. VPD measures how much water vapor the air is capable of holding. The higher the VPD, the greater the evaporation rate of water, leading to dehydration in both ecosystems and human airways. According to the study, the increasing VPD can trigger a significant inflammatory response in the body, worsening respiratory conditions and leading to increased vulnerability to airway damage.
The full study, published on March 17 in Communications Earth & Environment, also highlights how mouth breathing and greater exposure to air-conditioned or heated indoor environments can exacerbate these effects, leading to more frequent and intense dehydration and inflammation of the airways.
David Edwards, lead author of the study and adjunct professor of medicine at Johns Hopkins University School of Medicine, emphasized the importance of addressing air quality from both a cleanliness and hydration perspective: “Air dryness is as critical to air quality as air dirtiness, and managing the hydration of our airways is as essential as managing their cleanliness. Our findings suggest that all mucosa exposed to the atmosphere, including ocular mucosa, are at risk in dehydrating atmospheres.”
The study first investigated whether the process of transpiration, which causes water loss in plants, could occur in human mucus exposed to dry air. Transpiration has been shown to cause cell compression in plants, which can threaten their survival. The researchers hypothesized that the same compression might occur in upper airway cells under similar conditions.
To test this, human bronchial epithelium cells, which line the upper airways, were exposed to dry air. The results showed that the cells exposed to high VPD air had thinner mucus and elevated levels of cytokines, proteins that indicate inflammation. This confirmed the hypothesis that dehydration and thinning mucus in dry environments lead to cell compression, triggering an inflammatory response in the airways.
In an animal model, the team also examined the effects of dry air on healthy mice and mice with preexisting airway dryness (a common issue in chronic respiratory diseases). After one week of intermittent exposure to dry air, the mice with preexisting dehydration showed signs of immune cell activation in their lungs, indicating a high inflammatory response. In contrast, mice exposed only to moist air showed no such signs.
Through the study’s climate model, the researchers predict that by the latter half of this century, most of the United States will face increased risks of airway inflammation due to elevated temperatures and drier air. This highlights the growing importance of understanding and addressing how dry air impacts human health, particularly respiratory conditions.
The study’s authors also noted that the findings extend beyond the respiratory system, with potential implications for other physiological processes, including dry eye and the movement of water in the eye’s mucus linings.
“This manuscript is a game changer for medicine,” said study co-author Justin Hanes, Ph.D., the Lewis J. Ort Professor of Ophthalmology at the Wilmer Eye Institute, Johns Hopkins Medicine. “Human mucosa dehydration is currently a critical threat to human health, which will only increase as global warming continues. Without a solution, human mucosa will become drier over the years, leading to increased chronic inflammation and associated afflictions.”
David Edwards stressed that understanding how airways dehydrate in dry air is crucial for mitigating and potentially reversing the inflammatory effects through effective behavioral changes and preventive or therapeutic interventions.
This study underscores the need for further research into how the human body responds to increasingly dry air due to climate change. With the rising threat of global warming, dehydration and inflammation in the airways may become more prevalent, contributing to chronic respiratory conditions. The findings highlight the need for public health interventions, such as better environmental controls and therapeutic approaches, to manage the impact of air dryness on human health.
The research team included collaborators from institutions such as Boston University, Imperial College London, Sensory Cloud Inc., and the University of North Carolina. The authors reported no conflicts of interest.
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