What are you talking about? Especially vitamin D is researched to death. You think scientists are stupid? If there is a incidence difference along the north-south axis, it's the first hypothesis investigated.
Thing is, intervention usually doesn't prove very effective. That's why doctors aren't that hysterical about it.
Then some vitamin supplement studies have shown actually harmful, eg. vitamin A as antioxidant. Vitamin D is a hormone and regulates many processes in the body, e.g. a large dose suppresses the immune system similar to steroids... caution is definitely warranted, instead of blanket recommendations of the "Just take 5000IU/d! #YOLO" you find online frequently.
I didn't say researchers, I said in a medical context. If you do a search on pubmed or Google Scholar, you can find a lot of research on how vitamin D supplementation proved beneficial for patients in different contexts.
Also, I found your reply really jarring. Perhaps it's the immediate ad-hominem attack, but I just wanted to note that for your reference, it really didn't motivate me to want to engage any further with you.
Good thing I also mentioned doctors, who are, of course, applying the concluded result of research. But maybe you are talking about another "medical context".
I threw your "vitamin D supplementation proved beneficial" into Google and this Nature review article on vitamin D supplementation was the first result:
The vitamin/supplements industry makes billions while the pharma industry makes trillions.
The pharma industry is financially shaped around big "hit" patented medications that rake in megaprofits. They are literally too big to play in the vitamin-selling market.
It's kind of like how you and I might be able to spin up a profitable SaaS or other project that pulls in a few hundred grand or even a few million per year. A nice sum! Meanwhile, FAANG companies can't even consider such projects. They are not going to keep the lights on by pursuing 100,000 different niche projects that each make $100,000 profit per year. That would still only be 20% of their current revenue.
The big pharma companies shape how things are done. They fund the studies, they have direct access to doctors, etc.
In terms of actual influence the supplement industry might as well not even exist, just like our theoretical SaaS would have zero industry influence.
A quick search tells me the markets are much closer than that. R&D cost is lower and regulation isn't as strict so I wouldn't be surprised if selling vitamins is the more lucrative business. The pharma companies haven't missed this and they are also in the business.
The point is that relative to pharma, the supplements industry has essentially zero regulation and essentially zero barrier to entry.
Anybody can get into that game, and they do, judging by the thousands of different supplement peddlers one sees on Amazon and at the local CVS. Some of them even stick around for more than a year or two.
It can be a profitable business, but it's sort of a race to the bottom. I'm a fan of supplements, but if you think that selling Vitamin D pills at Safeway can gave you power and money on par with an international pharma company selling lifesaving cancer treatments at $10,000 a pop or whatever then what are you doing talking to me on HN? Go bottle some pills and think about what kind of superyacht you'll be buying.
Deficiencies seem like such a frequent occurrence but most patients end up needing to self-medicate.