ADVANCEMENT OF THE SCIENCE
adults (Thannickal et al., 2014). By 2034, for the first time in U.S. history, older adults are projected to outnumber children. On a global scale, the number of adults 65 years of age is projected to increase from 617 million in 2024 to >2 billion by 2050; further, it is estimated that within 25 years, older adults will account for 20% of the world’s population (Dzau et al., 2019). This demographic transition poses several challenges for healthcare, as there have been precipitous increases in diseases that dis- proportionately aict older individuals, such as cancer, cardiovascular disease, pulmonary conditions, and dementia. Research indicates that altering the biological processes impli- cated in aging can improve, delay, or alter the outcome of age-related diseases (Longo et al., 2015; Schneider et al., 2021). Advanced age causes progressive impair- ment of lung function in otherwise healthy individuals; aged lungs are marked by struc- tural changes that impair gas exchange and immunological changes that together pro- gressively handicap the lungs’ ability to respond to environmental stressors. The drivers of lung aging remain elusive, and an understanding of why age increases the risk of primary lung cancer, respiratory infec- tions, and chronic and fibrotic lung disease is lacking (Budinger et al., 2017). Peak lung function and maturation are observed between 18 and 25 years and stay relatively the same until 35 years, after which there is a decline as evidenced by progressive loss of alveolar surface area, air space dilatation, reduced mucociliary clearance, and change in elasticity (Schneider et al., 2021; Sharma & Goodwin, 2006). Furthermore, the aged lung is associated with stem cell exhaustion and senescence of pulmonary cells; limitation in the remodeling and repair of the extracellular matrix; and alteration of the pulmonary surfac- tant system, mucociliary clearance, or pulmo- nary nervous system, which in turn increases the susceptibility of older individuals to lung injuries and diseases (Brandenberger & Müh- lfeld, 2017). This decline in lung function is a direct result of underlying cellular changes that impact structural, functional, and mechanical features of the respiratory system. Pulmonary Immunity and Aging Advancing age leads to immune dysfunction and a heightened inflammatory state. Dys- regulation of pulmonary innate immunity
FIGURE 1
Deaths in the United States From Work-Related Respiratory Diseases
35,000
1995–2004 2005–2014
30,000
25,000
20,000
15,000
10,000
5,000
0
15–24 25–34 35–44 45–54 55–64 65–74 75–84
≥85
Age (Years)
FIGURE 2
Deaths by Age of Residents in the United States, 1995–2004*
14,000 13,000 12,000 11,000 10,000
9,000 8,000 7,000 6.000 5,000 4,000 3,000 2,000 1,000 0
15–24 25–34 35–44 45–54 55–64 65–74 75–84
≥85
Age (Years)
Coal Workers' Pneumoconiosis and Related Exposure Byssinosis and Related Exposure Malignant Mesothelioma
Asbestosis and Related Exposure Silicosis and Related Exposure All Pneumoconiosis and Related Exposure Hypersensitivity Pneumonitis
*Years covered are 1999–2004.
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Volume 87 • Number 3
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