Younger lungs
MILE 1: Your lungs expand, and the more oxygen-rich breath you draw causes your capillaries to dilate and exchange waste gases for fresh more easily.
MILE 1000: You use oxygen more efficiently. Your higher levels of vitamin D from all that daylight make your lungs less prone to inflammation and subsequent disease. Decades of gradual aerobic function decline have been wound back, potentially giving a 50-year-old the lungs of their twenties.