Question is, is food-additive Vit D as effective as skin-produced Vit D?
Apparently, as the nationwide deficiency causing rickets was what led to Vitamin D fortifying butter and milk decades ago, my understanding is that the cases dropped exponentially afterward.
Good question that I don't think I've seen answered directly. But I've seen nothing to say that supplemental vitamin D doesn't work.
There is one thing - adding vitamin D to foods did apparently do away with the formerly common rickets.
I’ve increased my Vit D supplements because of all the flu scare. There is a nasty bug going on here. Kid brought it home from school but it wasn’t too bad which may be because he’s outside often. Hubby, who doesn’t go outside, caught it and was in bad shape for a week. Then, I caught it but was over it in three days. Usually, I’m the one who is laid up with a chest infection at the least hint of a bug.
“...is food-additive Vit D as effective as skin-produced Vit D?”
Most D fortified food uses D2, not as effective or safe as D3. D3 results in the same effect in the body as that from sun exposure.
Note that ‘flu season’ is generally a winter months disease, when we have less vitamin D if we don’t supplement because of none from the sun. D3 supplementation of 10,000 iu is enough to provide a significant boost to the immune system (1,000 iu = 25 micrograms).
Some, including one MD I know, take as much as 50,000 units of D3 a day. At this level avoid all supplemental calcium - calcium could begin to concentrate in soft tissue (things like kidney stones, mitrovalve prolapse, etc). Magnesium supplementation is important, but no calcium. Osteoporosis is a magnesium deficiency.