> I use Carlson's, and I think most of the informed people are recommending about 2,000 units per day. John Cannell's site, 'the vitamin D council,' has a newsletter, and is a good way to keep up with the vitamin D research.
> I think getting enough vitamin D increases the ability to tan.
> During the winter for a couple of months 10,000 units of D should be safe, but it's better to increase [[calcium]] and [[vitamin K]], keeping the vitamin D a little lower unless you have the blood level checked occasionally.
> Usually 2000 i.u. during the winter will make up for no sunlight. Some people need 5000 iu according to their [[blood tests]], to keep it in the middle of the range.
> [Blood test] I think 50 ng/ml is a good goal. The point at which it lowers parathyroid hormone would be the right amount.
> [Causes of low vitamin D] I’ve seen some quick improvements from serious symptoms with a supplement of it. I think low [[thyroid]] could increase the need for it. It takes lots of summer [[sun]] direct exposure of a lot of [[skin]] to make enough vitamin D.
> [D3 supplement lowered length of hospital stay and mortality for intensive care patients.] [(Reference)](https://archive.ph/o/OJZkW/https://raypeatforum.com/community/threads/ray-peat-email-advice-depository.1035/page-8%23post-56348)
> [What do you do for vitamin D levels in winter?] In addition to a few quarts of milk with added vitamin D, and eating liver, I rub several drops of the vitamin D oil onto my skin, and occasionally use an ultraviolet light. [Source](https://lowtoxinforum.com/threads/ray-peat-email-advice-depository.1035/post-280105)
> [I noticed you mention eating liver, could I ask the relationship between liver and vitamin D?] The liver catalyzes the hydroxylation of cholecalciferol to 25-OH-colecalciferol, and many nutritional deficiencies can effect the liver's functions. I've known several liver-avoiders whose serum 25-OH-Vitamin D stays low despite big doses, and I suspect their general nutrition is responsible. It's reasonable to feed their liver optimally. [Source](https://lowtoxinforum.com/threads/ray-peat-email-advice-depository.1035/post-280105)
> [When you use vitamin D on your skin during the winter what dose do you use?] About 20,000 iu. [Source](https://lowtoxinforum.com/threads/ray-peat-email-advice-depository.1035/post-257079)