Smokers and Cyanocobalamin

In one study, smokers were found to excrete 35% more B12 than nonsmokers (1). In another study, smokers' serum B12 did not differ from nonsmokers', and the Institute of Medicine concluded that "The effect of smoking on the B12 requirement thus appears to be negligible." (1)

Hydroxocobalamin injections decreased blood cyanide levels by 59% in smokers (1.5-3 packs/day); cyanide was eliminated in the urine as cyanocobalamin (2). This indicates that cyanocobalamin may be actively excreted rather than used in people with elevated cyanide levels. Thus, I am concerned that vegan smokers may not receive much benefit from cyanocobalamin supplementation. Most smokers have an intake of hydroxocobalamin, and other non-cyanocobalamin forms of B12, through animal foods, which can counteract their bodies excretion of cyanocobalamin. Unless vegans take a non-cyanocobalamin supplement, they do not have a non-cyanocobalamin source of B12.

In contrast, I know two vegan smokers whose B12 source has only been cyanocobalamin, and who have not developed overt B12 deficiency in over ten years on the diet. There are probably others. Unfortunately, I could find no studies looking at cyanocobalamin supplementation in smokers, much less in vegan smokers.

To be cautious, I am suggesting that vegan smokers supplement with a non-cyanocobalamin form of B12. The amounts will have to be somewhat arbitrary because of the lack of information on the absorption rates and detoxification action of the various forms of B12 in smokers. I have not seen evidence of oral adenosylcobalamin's effectiveness in counteracting B12 deficiency. Donaldson had success with oral methylcobalamin. I would, therefore, tentatively recommend 500-1,000 µg/day of methylcobalamin.

It could be that the recommendations for vegan smokers need not be any different than those for nonsmokers. At this time, I do not feel that there is enough evidence one way or the other.

There is no evidence that cyanocobalamin is harmful to vegan smokers; including a modest source of cyanocobalamin (e.g., 3-5 µg/day), in addition to methylcobalamin, could serve as insurance.


1. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press; 2000.

2. Forsyth JC, Mueller PD, Becker CE, Osterloh J, Benowitz NL, Rumack BH, Hall AH. Hydroxocobalamin as a cyanide antidote: safety, efficacy and pharmacokinetics in heavily smoking normal volunteers. J Toxicol Clin Toxicol. 1993;31(2):277-94.