I switched from the more easily-swallowable cyanocobalamin to a sublingual methylcobalamin for this and the other reason.
My doctor also instructed me to eat more red meat. Anemia runs in my family (on the feminine side) to the point where my mother has had to have blood transfusions to save her life. I'm a male with a similar problem to a far lesser degree. While I aim to eat enough iron-rich foods, to boost the absorption I was also instructed to up my B12 intake as iron has traditionally been understood to be a bit easier to overdo. Food was always recommended over supplementation as well, but it's often not enough.
Also folate intake can mask B12 deficiency so it is always good idea to have buffer of Vitamin B12 in your body when starting on iron supplementation. The food will rarely help as in most cases B12 deficiency is not because of less B12 rich food is eaten but because our body can't absorb it properly. So sublingual and intramuscular intake is preferable.
For which reason, in spite of the potential inconclusiveness of these results, I am mildly concerned about the parent subject.
I used to be a smoker. After quitting and having some tests done by my doctor he said that my lungs should be back to functioning/health as if I'd never smoked inside of 4-5 years (so long as I didn't relapse. That hasn't been a problem). We didn't discuss chances of lung cancer in spite of that. If it's true that the supportive effects of B12 supplementation even on ex-smokers exponentially increases chances, then it becomes even more concerning.
Nearly all studies that have shown a beneficial effect of B12 have been done with cyanocobalamin, though methylcobalamin is more bioavailable (ie. it's "absorbed better").
