The amount available in food is insignificant. Early humans achieved the "ancestral" blood level of 45 ng/ml by running around naked under an equatorial sun. If you don't live near the equator, or if you are in the habit of wearing clothing or if you spend a lot of time indoors, or if you have dark skin, you won't get enough D3 without supplementation.
I have personally found it necessary to take 10,000 IU per day in order to reach the desired blood levels (your mileage may vary: take a $35 Vitamin D blood test to find out). This means two 5000 IU pills per day, or 730 pills per year. My preferred supplier charges about $7.50 for a bottle of 60, so it costs me about $92 per year. Since a high level of Vitamin D is associated with a reduced risk of the flu and pneumonia as well as the China Virus, this is an inexpensive investment. As a side benefit, I haven't had so much as a cold since starting this regimen, and I had no reaction to the China Virus vaccine; Vitamin D acts against excess inflammation, and extremely low levels were shown to be associated with hypercoalgulation :
Emerging Role of Vitamin D and its Associated Molecules in Pathways Related to Pathogenesis of ThrombosisIt takes a lot of exposure to sunlight to get to the point where vitamin D is effective. In some states and countries, there is very little sunlight. Furthermore, for some people, exposure to sunlight may lead to skin cancer.