I agree with V. Have your doctor test your current vitamin D levels in your blood before deciding how much you might need to take. Besides having RA or other autoimmune disease, there are other factors which effect how much D your body might need. For example, those who are obese (like me) need to take more D because our bodies tend to hoard it. I take 10,000 UL daily and that's admittedly quite a lot. Your doctor should be able to help you figure out how much you need for better health.
You have asked a good question. Since Vitamin D is not a water soluable vitamin, it can build up in your system. Too much Vitamin D is not a good thing.
I would suggest having your doctor check you Vitamin D with a simple blood test. That will tell your doctor what he/she needs to know to advise you on how much Vitamin D to take. There actually is a formula doctors use to calculate how much vitamin D you need based on your test results.
A lot of people with RA and Fibromyalgia do have low Vitamin D levels, and low Vitamin D can cause muscle and bone pain all buy itself...or so my doctor says.
Please get your blood tested and let us know the results. Best Wishes to you, Grandma. Please continue to post your questions or share your thoughts in a Sharepost. We have a lot of good, caring people on this site. We try to support each other. Welcome!