@Violeta -- You or your friend may want to check out the following video. Since watching it, I started taking 30,000 IUs of Vitamin D daily, and my tinnitus seems to have notched down a tad. Which I suspect is because it's lowering some inflammation somewhere in my ear or brain.
Vit. D3 is actually not a vitamin, but more accurately, a steroid hormone. The video is only about 4 min., but is quite good (and succinct). The video starts in the middle, so you may want to watch the first three minutes. Just to mention, I'll be monitoring my D3 intake carefully to make sure I'm not taking too much on a long-term basis.
I'm limiting myself to 30,000 IUs, but you can actually take more. Some people are taking as much as 75K IUs, and in one case, had their psoriasis completely go away. The maximum amount a person can take is likely to be highly individualized. But I've read that your body can require much larger amounts during times when it needs it, so "high dose" may not necessarily be "high-dose" if your body can actually use it.
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I didn't realize that one could safely take such high doses of vitamin d and that it could take such a long time for levels to improve. Although I sometimes look through the vitamin d wiki to see all the things it's good for. I appreciate this info for myself, and will tell my friend about it.