Effect of Vegetarianism and Smoking on Vitamin B12, Thiocyanate, and Folate Levels in the Blood of Normal Subjects

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Abstract
Vitamin B12, thiocyanate, and folate levels in the blood were estimated in 69 apparently normal subjects, of whom 26 were non-vegetarian non-smokers, 19 non-vegetarian smokers, 15 vegetarian non-smokers, and nine vegetarian smokers. The serum total (cyanide-extracted) B12 level (value A) ranged from 105 to 728 pg/ml, with a mean of 292 pg/ml. The highest values were found in non-vegetarian non-smokers and the lowest in vegetarian smokers. There was no significant difference in value A between smokers as a group and non-smokers as a group. On the other hand, in vegetarians value A was very significantly lower than in non-vegetarians regardless of their smoking habits. It is suggested that A may represent both the protein-bound and free forms of vitamin B12 in the blood, and B mainly the free B12, which may be the physiologically active form. The plasma thiocyanate level varied from 1·0 to 15 μmol/100 ml, being, as expected, much higher in smokers (mean 8·20 μmol/100 ml) than in non-smokers (mean 2·02 μmol/100 ml). There was a rough correlation between falling B12 levels and rising thiocyanate levels. The serum folate level ranged from 2·75 to 15·75 ng/ml, and was slightly but significantly higher in vegetarians (mean 6·60 ng/ml) than in non-vegetarians (mean 4·79 ng/ml), reflecting the greater content of folate in a vegetarian diet.