using a multivitamin daily is considered 'expensive' ?

Trying for a rough estimate of the yearly cost of taking a multivitamin daily, I get about $10 USD a year. For the 15% of the global population that live on less than $2 a day, that's around a week's wages. For the 56% that live on $2 - $10 a day, it's slightly more affordable, but still a significant cost.

Now, that's a cheap multivitamin, so it's got about 300IU of vitamin D, which is a pretty small dose. At a guess it's probably cheaping out on some of the other ingredients as well. On the other hand, ingredients bought in bulk and distributed through outlets in the developing world with very low overhead might be more affordable.

EDIT: the numbers for global poverty are probably out of date, but you get the point

10-20$ a year, compared to just D which comes down closer to 2-3$ a year. And again considering the other vitamins are much easier to come by. D is usually the ones that's more commonly lacking, especially in northern places.

Mushrooms? Salmon? Liver? Eggs? All of these have vit D without being fortified (mushrooms being a bit debatable as to if its fortified)

And its a little misleading not to talk about sunlight - technically that's not a food, but you were kind of implying you couldn't get it from the natural environment.

Vitamin D2 + D3 per 100g portion of mushrooms, according to this website from the USDA Agricultural Research Service (https://fdc.nal.usda.gov/)

- Mushrooms, raw: 0.2 µg (7 IU)

- Mushrooms, Chanterelle, raw: 5.3 µg (212 IU)

- Mushrooms, enoki, raw: 0.7 µg (29 IU)

- Mushrooms, maitake, raw: 28.1 µg (1123 IU)

- Mushrooms, morel, raw: 5.1 µg (206 IU)

- Mushrooms, oyster, raw: 0.7 µg (5 IU)

- Mushrooms, portabella, raw: 0.3 µg (10 IU)

- Mushrooms, shiitake, raw: 0.4 µg (18 IU)

- Mushrooms, white, raw: 0.2 µg (7 IU)

As you can see, there are many types of mushrooms and most of them do not have much vitamin D. Some do, but unless you are a mushroom nerd you are getting the wrong kind.

Young adult daily recommended dose = 1000 IU

Just came across this fascinating review:

https://fungi.com/blogs/articles/place-mushrooms-in-sunlight...

267,000 IU after exposing mushrooms to 14 hours of UVB?

Holy cow.

So, much like humans, mushrooms produce vitamin D from sunlight?

How much vitamin D is in a mushroom is going to depend more on how they are grown and stored then on the particular species afaik (in particular how much uv radiation it is exposed to).

I believe also that there will be more vitamin D in mushrooms that are irradiated to give them a longer shelf life. I don't think usa is a country where that practise is common, but i believe it is common in some other countries.