Is Ergothioneine the Longevity Vitamin?

Ergothioneine is an amino acid found mainly in mushrooms as a dietary source, but only a few other sources contain substantial amounts. It is called the longevity vitamin by reputable researchers, including RB Beelman et al., who noted in the Journal of Nutritional Sciences (Cambridge) that "We believe that ergothioneine is a 'longevity vitamin' that is limited in the American diet."