I have a lot to say about this because I think it’s critically important, simple, and it’s a tragedy so few people know.
First, few people know that vitamins generally reduce our life expectancy. The science on that is well established but, as with most things, marketing is far more effective than science in public opinion.
B12 is different. It’s from bacteria in soil and before the age of sterilization everyone got enough. Animals are simply carriers. They get it from unsterile conditions or supplementation.
Estimates vary, but what’s clear is a significant portion of the population is deficient, especially as you get past 50 and your ability to absorb goes down. By age 80, you probably need B12 shots in the butt or risk neuropathy. Neuropathy causes the elderly to lose their balance. It’s not reversible and is responsible for many a broken hip. Tragic, because B12 supplementation is relatively easy. Even Madonna administers B12 pricks (shots) into the butts of her dancers.
The paper you referenced from the team in Milan was extremely well written, imo. I read it very carefully. My only concern is it (by design) eliminated people who have trouble maintaining B12 levels because of illness or age. That’s a lot of people who really need it.