I wouldn't suggest cod liver oil for ramping up vitamin D levels if you're low, but if you just need to maintain, it can be part of a good daily regimen, in my opinion. We also eat salmon a few times a week and drink raw milk daily; both of these have vitamin D in them. The best source is time in the sun but you probably know that.
It's a small amount and it depends on the brand. I use Rosita cod liver oil - https://www.rositausa.com/products/extra-virgin-cod-liver-oil-softgels?variant=33305959563308 125 IU for 3
I wouldn't suggest cod liver oil for ramping up vitamin D levels if you're low, but if you just need to maintain, it can be part of a good daily regimen, in my opinion. We also eat salmon a few times a week and drink raw milk daily; both of these have vitamin D in them. The best source is time in the sun but you probably know that.