Humidifiers: Enhancing Immunity Against the Flu in Dry Conditions
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Chapter 1: The Role of Humidity in Respiratory Health
As temperatures drop and heating systems kick in, indoor air often becomes less humid. This decrease in humidity not only leads to discomfort—dry skin, nasal passages, and throats—but also negatively affects the innate immune system's ability to function properly within the respiratory tract.
The respiratory system encompasses more than just the nose and mouth; it includes the throat, bronchi, and lungs, all lined with epithelial cells that produce mucus. This mucus serves as a critical first line of defense against viral infections, including influenza and COVID-19.
The epithelial cells feature tiny hair-like structures known as cilia, which help move mucus out of the respiratory system, aiding in the expulsion of pathogens and particulate matter through coughing, sneezing, or blowing the nose.
A study found a significant link between decreased humidity and increased mortality rates from influenza. Researchers observed that mice infected with the influenza virus at lower humidity levels experienced more severe illness. Specifically, those in environments with 10% or 20% humidity exhibited a quicker onset of sickness compared to those in 50% humidity.
The findings indicated that low humidity interfered with mucus clearance and weakened the innate immune response. Analysis revealed that, in lower humidity, the mucus became too thick for cilia to effectively move.
Examinations of the lungs showed that mice in low humidity had the virus present in both epithelial cells and macrophages, while in 50% humidity, the virus was only found in macrophages. Macrophages are essential immune cells that eliminate pathogens and infected cells, suggesting that low humidity hinders the immune system's ability to combat viral threats.
In addition to viral presence, lung inspections six days post-infection showed that mice in low humidity exhibited reduced tissue repair, aligning with more severe symptoms and higher mortality rates.
Gene expression analysis in the lungs of these mice revealed that those in low humidity had diminished activation of genes responsible for antiviral responses. Collectively, these findings offer insights into why influenza infections are seasonal and suggest a straightforward method to decrease the risk of infection and alleviate symptoms: using humidifiers when heating is necessary.
Highlighted Article
- Kudo, E. Song, L. J. Yockey, T. Rakib, P. W. Wong, R. J. Homer, A. Iwasaki. Low ambient humidity impairs barrier function and innate resistance against influenza infection. Proc. Natl. Acad. Sci. U. S. A. 116, 10905–10910 (2019). DOI:10.1073/pnas.1902840116
Chapter 2: Preventing Influenza with Humidity
In this video, recent research highlights effective strategies to maintain humidity levels and consequently reduce the risk of influenza infections.