When you look at large-scale studies of OTC vitamins, you quickly realize that the absorption on most of them is very poor; they don't really move the needle very much. In most cases, you will be better off if you address vitamin and micronutrient deficiencies through diet rather than attempting supplementation.
The same goes for pregnancy, where you essentially gain a deficiency because you're building another person inside you.
I'm D deficient. I took D supplements for a long time; m D levels never significantly increased.
n=1, best study ever.
https://www.nature.com/articles/s41574-021-00593-z
When you look at large-scale studies of OTC vitamins, you quickly realize that the absorption on most of them is very poor; they don't really move the needle very much. In most cases, you will be better off if you address vitamin and micronutrient deficiencies through diet rather than attempting supplementation.