Why did I start taking D3? I ran over 60,000 miles and my knees were killing me. I read a study from the 1930s that used 250,000 iu D3 up to 2 million iu daily for RA. I took 1/5 of the lowest dose that was used. In 60 days my knees were fine and I continued to run for another 8 years. I still have no knee pain and walk for exercise. MRIs of my knees told me I have no meniscus in either knee and had bone on bone wearing away both joints. I was told to immediately have 2 knee replacements as My knees would not get better. I have not had any knee surgery 15 years later. Jeez maybe I should have consulted Dr. JD The major finding of this case series is prolonged daily dosing of vitamin D3 with doses of 10,000 to 60,000 IU was safely tolerated. https://pubmed.ncbi.nlm.nih.gov/28012936/