I seriously doubt this was a scientific study to test the upper tolerance limits of vit D. I mean, no ethics committee on the planet would approve the dosage.
Bao YW, Yuan Y, Chen JH, Lin WQ. Kidney disease models: tools to identify mechanisms and potential therapeutic targets. Zool Res. 2018;39(2):72-86. doi:10.24272/j.issn.2095-8137.2017.055
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5885387/
Nishinakamura, R. Human kidney organoids: progress and remaining challenges. Nat Rev Nephrol 15, 613–624 (2019). https://doi.org/10.1038/s41581-019-0176-x
https://www.nature.com/articles/s41581-019-0176-x#citeas
With a nice, simple graph showing effects of Vitamin D levels on kidney function over time.