Have you not set foot in a poorer nursing home? You don't need a source to understand they aren't let outside much or given vitamin D. Just go pay those old people a visit and ask.
Very true. Drs understanding of magnesium is what vitamin D was in the 1990s.
I agree that most supplements are overrated unless you've got a serious health problem. Then they become very useful but it's hard and expensive to figure out what works. A high quality protein with magnesium does wonders as well. Amino acids are required to build a lot of important things in the body.
I was diagnosed with severe crohn's disease in the late 90s. Doctors started learning about Vitamin D and the immune system in the 2000s. My only specialist who knew about it in the 90s is now at an elite hospital. It was rare knowledge 20 years ago. Medicine is still pretty much stuck in the last century with nutrition knowledge. It's all about pushing pills for the most part. The synergistic study of different nutrients is still pretty lacking.
For example, most Drs now know about vitamin D. But do they know about A and K and the dosages and which minerals you should probably take with it when someone is extremely D deficient like in a lot of autoimmune patients? Probably not...
Do doctors know most patients with resections or digestive issues who are B12 deficient can absorb methylcobalamin sublingually? I've never met one that does.
I can go on. Most doctors understanding of B12 is still stuck in the 1970s along with most other aspects of nutrition.