You know vitality when you see it: the effervescent 75-year-old grandmother who swims two miles a day; the inspired florist whose passion for daylilies has you buying them by the dozen; the empathetic friend whose centered, calm demeanor seems to radiate inner peace. People with vitality overflow with that special something, and they stand out from the rest like shiny pennies.

All of which leads one to wonder: Why do some people have more vitality than others?

Since vitality is often broadcast via physical traits – sparkling eyes, radiant skin, an energetic attitude – it’s tempting to chalk it all up to good health. But there’s more to vitality than robust physiology. Not all clinically healthy and ostensibly fit people seem particularly vital, after all. And some physically frail individuals still manage to emanate an extraordinary life force and joie de vivre.