I had been taking Vitamin D supplements about 600IU per day for about 2 months, and had no ill effects and numerous positive effects which I attribute to the vit D (decreased muscle and joint pain, better moods, eliminating several minor skin conditions, better hair, better digestion, better sleep, just to name a few), though some of this might also be due to the Paleo diet.
I recently switched to a 5000IU per day gelcap from iherb, the main reason was that I ran out of my 200IU dry tablets and needed a replacement, and wanted something that came with oil. There aren't many reports of side effects at this dosage of vitamin D so I wasn't too worried about the increase.
Since the switch, I have been feeling slight soreness in my back about where my kidneys are (lower middle of my back on either side of the spine). I am not sure that this is actually kidney pain, as I've also been doing some new upper body workouts (Burpees and kettlebells) and it could just be muscle soreness from the workouts. I also had a period where I felt more sore, more moody, worse sleep, etc. basically a reversal of some of the benefits, though that has started to go away too.
I have read online that kidney stones can be caused by vitamin D (haven't found a lot of detail), though I don't think I contracted kidney stones in about 2 weeks. I have also read that increasing vitamin D can make you deficient in magnesium, and low magnesium has its own effects, including muscle soreness.
At this point I'm not really sure what is related to what, so my question is, for anyone that has started taking doses of vitamin D in the 5000IU+ range, have you had any muscle soreness or kidney pain/problems? I'm looking more for first-hand experience than something Googled up if possible, thanks.