I found this new study which I found disturbing, is it legit? https://www.theatlantic.com/health/archive/2017/08/b12-energy/537654/
I am a physician for 24 years and have been practicing Functional Medicine. I read this study and it does not state the form of the B6 and B12. Nor do they test the subjects' B6, B12 and folate levels before and after the testing. They didn't talk about so many other contributing factors. Folate, and B12 in the methyl form is the usable form. Those two join homocysteine to for Methionine. Then into SAM in the mitochondria to replicate new healthy cells. The process I just described is called methylation. Means making new cells to replace older dying ones. When this is out of balance, you will not have all the parts of the body to replicate new healthy cells. This leads to all sorts of Chronic diseases including cancers. You can accurately test for all the levels through serum B12 and MMA, serum folate a Figlu. This tells you not only how much was absorbed in the body but also what actually makes it inside the cell in the right form. Never guess, test when you're in a serious situation with a Functional Medicine Physician which will find the cause of your illness through specialized proven lab methods.
Hope this helps