Based on my understanding, the main problem surrounding too much Vitamin D is with high levels of calcium that develop. Vitamin D plays a big role as a calcium

Based on my understanding, the main problem surrounding too much Vitamin D is with high levels of calcium that develop. Vitamin D plays a big role as a calcium-regulatory hormone, and too much of it can lead to elevated levels of calcium in the blood. However, in a normal, healthy adult, the body's own feedback-inhibitory mechanisms will just downregulate synthesis of the hormone when too much calcium is detected in the blood. If you're sick or have other things going on (like cancer or taking too many Vitamin D tablets), however, it can be a problem: Papapetrou PD, Bergi-Stamatelou M, Karga H, Thanou S. Hypercalcemia due to sun exposure in a patient with multiple myeloma and elevated parathyroid hormone-related protein. Eur J Endocrinol. 2003 Mar;148(3):351-5. doi: 10.1530/eje.0.1480351. PMID: 12611617. https://pubmed.ncbi.nlm.nih.gov/12611617/ https://pubmed.ncbi.nlm.nih.gov/12611617/ Use of vitamin D drops leading to kidney failure in a 54-year-old man Bourne L. Auguste, Carmen Avila-Casado, Joanne M. Bargman CMAJ Apr 2019, 191 (14) E390-E394; DOI: 10.1503/cmaj.180465 https://www.cmaj.ca/content/191/14/E390 https://www.cmaj.ca/content/191/14/E390 Naik MA, Banday KA, Najar MS, Reshi AR, Bhat MA. Vitamin D intoxication presenting as acute renal failure. Indian J Nephrol. 2008;18(3):125-126. doi:10.4103/0971-4065.43693 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2813130/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2813130/ "Hypercalcemia is a condition in which the calcium level in your blood is above normal. Too much calcium in your blood can weaken your bones, create kidney stones, and interfere with how your heart and brain work." https://www.mayoclinic.org/diseases-conditions/hypercalcemia/symptoms-causes/syc-20355523#:~:text=Hypercalcemia%20is%20a%20condition%20in,result%20of%20overactive%20parathyroid%20glands https://www.mayoclinic.org/diseases-conditions/hypercalcemia.... Here's the graphic on Vitamin D synthesis in the body from Wikipedia, you can see that the enzyme CYP27B1 is inhibited by elevated levels of calcium in the blood, so calcidiol is shunted into production of an inactive metabolite. This is what would be happening if you were out sunbathing for 123123 hours per day. https://en.wikipedia.org/wiki/File:VitaminDSynthesis_WP1531.png https://en.wikipedia.org/wiki/File:VitaminDSynthesis_WP1531....