"[...] extended the cellular lifespan of human skin and lung cells by more than 50%"
If we assume that the effect is the same for all types of cells, it follows that the life is extended by 50% (when keeping "all other factors" constant, as usual).
If we assume that the effect is the same for all types of cells, it follows that the life is extended by 50% (when keeping "all other factors" constant, as usual).