https://vitamind3-cholecalciferol.com/vitamin-d-co-factors/
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Vitamin D requires a small amount of vitamin A (retinol) in order to function. But vitamin A and vitamin D attach themselves to the same cell receptors. If you have too much vitamin A, it grabs those cell receptors and leaves no room for vitamin D.
So even though you might take enough vitamin D, it can’t work properly if you also have too much vitamin A (retinol).
We recommend supplementing no more than 2000 IU of retinol daily. But make up for it with extra beta-carotene.
Beta-carotene is a vitamin A precursor found in some green, yellow and orange vegetables.
You can take in as much beta-carotene as you please if you obtain it from vegetables.
If you don’t eat enough vegetables, take a beta-carotene supplement, about 5000 IU (3 mg) daily.
Your body will get all the vitamin A it needs by converting beta-carotene to retinol. This process is regulated, so your body will never create more retinol than it requires, and not enough to get in the way of your vitamin D.
