Aging and Viral Respiratory Infections: Focus on Vitamin D and Microbiota

Viral respiratory infections in older adults tend to be more severe and linked to increased mortality. Factors such as lung aging and changes in its structure and function; aging of the immune system and decrease in its function with age; and inflammaging, the accumulation of senescent cells with age with senescence-associated secretory phenotype (SASP) (is a secretory profile that includes the secretion of inflammatory cytokines, growth factors, chemokines, and matrix-metalloproteinases) leads to an increase in the susceptibility and vulnerability of older adults to respiratory infections. Malnutrition and micronutrient deficiencies, including rising rates of vitamin D deficiency, can also exacerbate respiratory infections in older adults. Vitamin D plays a role in maintaining epithelial integrity and has anti-inflammatory properties. Vitamin D enhances innate immune responses and suppresses adaptive immune responses, thereby restoring the immune system to homeostasis. Vitamin D deficiency is associated with microbiota dysbiosis and inflammation, and higher vitamin D levels are associated with greater abundance of beneficial, protective microbiota against respiratory infections. A more profound comprehension of the advantageous impacts of vitamin D in respiratory viral infections, particularly the relationship between vitamin D and the microbiota, will provide new perspectives on the importance of vitamin D assessment and standardization.