That's what I assumed from other readings. Why, then, can I only find studies administering B12 near the time of the surgery? Those studies still found protective effects on homocysteine elevation, but that may be mostly due to the coadministered B9.

This means B12 should be taken either well before NO, or sometime after. Given the short half life of NO, it should be fine to take B12 orally immediately after a final NO dose; the B12 will be absorbed shorty after the NO is eliminated.

Note that, though folate and B12 were given IV before and after surgery, it did not have an immediate effect. The NO induced rise in homocysteine was not blunted by the end of surgery. However, postoperative homocysteine was lowered to below baseline on all 3 measurement days. The NO induced rise in homocysteine lasted 2 days postoperatively.

Unsurprisingly, this suggests a lag time between B vitamin administration and homocysteine drop. Thus, what I'd really like to see is a study administering B vitamins 1 day prior to NO use.

This suggests those taking NO should supplement with both B9 and B12. It is likely that the effects on B9 are more acute, while B12 deficiency probably only becomes an issue with chronic abuse or in those with borderline B12 status to begin with.

This provides some reason to be agnostic as to whether vegans can obtain B12 naturally. Of course that shouldn't matter to any rational person (who'd just take a supplement). Note that I was searching for this info, and this is the first piece of evidence I found. Thus, I suspect there is more evidence since 1965. I'll try to tag updates with "nativeB12"

Recommended way, then...