Vitamin B12 - Smoking and Vegetarians

Smoking
Cigarettes have a high cyanide content that can interfere with B12 metabolism. In one study, vitamin B12 loss in urine was significantly higher among smokers than nonsmokers. However, in other studies the difference has been negligible.

Vegetarian
Because B12 comes from animal products, people who follow a strict vegetarian or vegan diet are at risk for vitamin B12 deficiency. This also holds true for babies who are breastfed by vegan mothers. These infants begin to show signs of deficiency at about four months of age. Therefore, infants at risk of B12 deficiency should be supplemented with the Adequate Intake (AI) for vitamin B12 from birth.