Why does lung function decline as people age?

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As people age, lung function declines due to several structural and mechanical changes within the respiratory system.

Mechanical and Structural Changes

The decline in lung function is largely driven by the following factors:

Reduced Chest Flexibility: The bony cage of the chest becomes stiffer, and the muscles responsible for moving the chest during respiration lose strength.1
Loss of Elasticity: The lungs rely on elastin and collagen for their elastic properties. Aging leads to the formation of cross-links in these proteins, which reduces the lung's ability to expand and recoil.1
Capacity Shifts: Vital capacity—the total air expelled after a deep breath—diminishes, while the volume of air that remains trapped in the lungs increases.1

Oxygen Transfer

While the ability to transfer oxygen and carbon dioxide decreases slightly with age, this impairment is most noticeable during strenuous activity. This is primarily attributed to a reduced ability to adjust blood flow to the air sacs within the lungs. Lifestyle factors, particularly smoking, significantly accelerate these declines, often mimicking the respiratory profile of someone 10–15 years older.1