Earlier quoted context omitted.
Vitamin D is still being discussed quite a lot on HN. My understanding is that it boils down to "It helps those who are deficient but doesn't do much, if anything, if you aren't deficient." Now, a lot of people are deficient -- probably more now than usual due to the lock down because people aren't getting out much, so people are getting less sun exposure. So I tend to get downvoted when I say things like "If you are…
Is it not any different than suggesting obese people get in shape to reduce their risk? Low-hanging, non-risky fruit first.
It pretty much is a slam dunk solved problem to say "If you are deficient in X, redress that." We know how to redress a vitamin D deficiency pretty confidently, simply and in a straight forward fashion.
I lost several dress sizes without trying by redressing other things, primarily nutrient deficiencies. I focused on eating an aggressively nutritious diet to redress a long list of deficiencies rooted in a genetic disorder that causes gut dysfunction.
So my experience fits with the general idea that "Solving obesity is harder than it looks and the solution may be something non obvious in any given case." Maybe our mental models of what is going on there will evolve and what I am saying will be "the obvious answer" to future generations, but it's not what is currently believed to be what works to solve obesity.
The current mantra is "Calories in. Calories out." and leads to metrics like "Eat less and exercise more" and some people find that wholly unworkable or unsustainable for various reasons.