I think it means one should read the very next sentence:

> Pieper emphasized that current over-the-counter NAD+-precursors have been shown in animal models to raise cellular NAD+ to dangerously high levels that promote cancer. The pharmacological approach in this study, however, uses a pharmacologic agent (P7C3-A20) that enables cells to maintain their proper balance of NAD+ under conditions of otherwise overwhelming stress, without elevating NAD+ to supraphysiologic levels.