Off the top of my head, USDA created daily requirements for vitamins like D shortly after the 30's, when rickets (which had been very common) interfered with the draft.
rickets was about bone density, long-bone growth and bowed/feeble legs mostly, especially in shut-in climates, urban centers and during child labor years.
Required adding it to milk and some other things like breakfast cereal, plus the food stamp program got the work and draft age population up to top fitness in the history of the world.
Higher D doesnt sound that dangerous, since as with natural sources like sunlight, it depends on the presence of some other nutrients for bioavailability, and does not become toxic (stored in fat-soluble places like brain and organs) no matter how much capn crunch with milk we eat.
might be wise to look up the combination foods that will make it absorbable and usable.