In plain terms: Procyanidin C1 (PCC1) 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.
Procyanidin C1 (PCC1)
The evidence as the record states it
Xu et al. (Nature Metabolism, 2021; PMID 34873338): PCC1 selectively eliminated senescent cells, possibly by promoting reactive oxygen species production and mitochondrial dysfunction, and extended health and lifespan in mice; a supplement company funds senolytic research in the senior author's laboratory, the authors hold a related patent, and co-authors have senolytic company and patent interests. That paper is now the subject of an Expression of Concern issued by Nature Metabolism in March 2026 (PMID 41731120), so its findings are under question by the journal that published them. Liu et al. (PNAS, 2024; PMID 38657052): a later mouse study from another group reporting senolytic and senomorphic effects in the aged retina. No human trial published as of October 2026. The Grade D is unaffected, because D already reflects the absence of any human trial.
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: procyanidin C1 OR PCC1 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.