The amount of Vitamin D in "fortified" milk is enough to keep kids from having rickets. Usually 400 iu per serving. As an adult, that's enough to get your blood 25-D level up to 4 ng/ml. It's pitiful. They don't add it to anything but milk. It's not present in your diet, unless you eat oily fish. The way most people got enough was they made it from sun exposure. 20 minutes in strong sun with your shirt off gives you about 10,000 iu! Life guards average about 70 ng/ml blood levels. All sorts of diseases are much improved at 40 ng/ml and some like MS at 70 ng/ml.

Unfortunately, most Americans don't get enough sun or eat enough oily fish. Or they go out in the sun slathered in sunblocker which prevents Vitamin D synthesis. Deficiencies are very common, and extreme deficiencies are common in Black people. Seasonal deficiencies are why we get flu in the winter.

Of course, living in Florida, you can easily get enough sun to stay healthy. It worked at sanitariums before they had antibiotics. It worked in 1918. Still works.