A large body of evidence indicates that forms of air pollution harm long-term health. This is largely epidemiological data, observing correlations with incidence of mortality and age-related disease in populations exposed to different levels of pollutants. A number of regions of the world exhibit, through happenstance, very similar populations that are exposed to significantly different levels of particulate and chemical pollutants. Consider studies covering the Puget Sound in the US or parts of China. These natural experiments provide an increased confidence that the observed correlations are a matter of air pollution causing harm to health.
The primary mechanism by which air pollution is thought to accelerate the onset and progression of age-related disease is via induction of chronic inflammation. Airway exposure to pollutants stresses cells, changes their behavior, and contributes to the burden of continual, unresolved inflammation that is characteristic of aging. This exposure exists on a spectrum, with smoking and indoor wood smoke at one end and the less severe degrees of industrial pollution in wealthier parts of the world at the other. Since effects are driven by inflammation, we should expect near all age-related conditions to be aggravated over time by exposure to air pollution, scaling by the severity of the exposure.
Emerging evidence suggests that air quality may impact muscle health. However, most studies are limited by cross-sectional designs or short follow-ups. We assessed the association of long-term exposure to ambient air pollutants with changes in muscle mass and strength in older adults. We included 3,249 participants from the SNAC-K longitudinal study (mean age 74.3 years; 35.8% males). Muscle strength (measured through handgrip and chair stand tests), muscle mass (derived from calf circumference) and physical performance (assessed through walking speed at a usual pace) were assessed over a 12-year period. Probable sarcopenia was defined as reduced muscle strength as per the EWGSOP2 criteria. Residential exposure to PM2.5, PM10, and nitrogen oxide (NOx) was estimated for the 5 years preceding baseline. Cox regressions and linear mixed models examined the association of air pollutant exposure with, respectively, probable sarcopenia and longitudinal changes in muscle parameters.
Over 12 years, the cumulative incidence of probable sarcopenia increased with higher exposure (above vs. below the median values) to NOx (36% vs. 28%), PM2.5 (35% vs. 28%) and PM10 (35% vs. 28%). The association between air pollutant levels and the risk of probable sarcopenia was nonlinear, with an increased risk showing a plateau at very high levels. Higher exposures were associated with an increased risk of developing probable sarcopenia, by 25% for NOx and PM2.5 to 33% for PM10. Elevated pollutant exposure was associated with significantly greater annual declines in lower-limb strength (chair stand test: 0.40-0.48 s) and walking speed (0.004 m/s).
Thus long-term exposure to moderate levels of ambient air pollutants may increase the risk of probable sarcopenia and accelerate declines in lower-limb strength and physical performance in older adults.
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