In plain terms: Apigenin has not yet been tested in a human trial designed to measure the outcome relevant here. The available human research does not yet answer the question.
Apigenin
The evidence as the record states it
Escande et al. (Diabetes, 2013; PMID 23172919): apigenin inhibits CD38 in cells and raises NAD+ and improves glucose and lipid measures in obese mice; this is the paper that shows apigenin as a CD38 inhibitor. Kellenberger et al. (Bioorg Med Chem Lett, 2011; PMID 21641214): other flavonoids (luteolinidin, kuromanin, luteolin) inhibit CD38 at low micromolar concentrations; the abstract does not name apigenin. Henderson et al. (npj Aging, 2024; PMID 38302501): a double-blind randomized crossover trial in humans of a branded multi-ingredient supplement, which raised whole-blood NAD+; it does not grade apigenin alone, and the maker's founder and chief executive and one of its employees are among the authors. D Route 1: no human outcome trial of apigenin by itself.
Why Grade D Route 1 and not Grade C
Grade D Route 1 applies when no qualifying human randomized trial has tested this compound or intervention against the relevant endpoint. Absence confirmed: apigenin supplementation AND randomized controlled trial[pt] AND humans[mesh] (PubMed, October 2026)
The first qualifying human RCT with a meaningful endpoint would move this to Grade C or higher, depending on what it shows.
What would move this grade
The first qualifying randomized controlled trial in humans, testing this intervention against a meaningful aging-relevant endpoint, would initiate grading. Depending on the result, it could land at any grade from A to D.