Vitamin B12 deficiency can be a risk of an alternative diet (it is not present in plant foods). Direct nutritional determinants of homocysteinaemia are vitamin B12, folic acid and vitamin B6. Hyperhomocysteinaemia is a non- lipid risk factor of vascular disease. Homocysteine plasma levels were assessed in a group on an alternative diet (lactoovovegetarian children and adolescents) and compared with an average sample on a traditional diet (omnivores). In vegetarian groups significantly higher homocysteine levels were found (9.25 vs. 7.34 mmol/l in children, 11.33 vs 8.02 mmol/l in adolescents) with a finding of hyperhomocysteinaemia in 19% children (above 9.64 mmol/l) and 40% adolescents (above 10.94 mmol/l) vs 0% in omnivores. Under conditions of a low methionine intake (alternative diet) the remethylation route of homocysteine breakdown predominates. Therefore the deter- minants of this route were evaluated. The RDA for vitamin B12 is met by vegetarian children and adolescents by 94% and 107% vs. 221% and 309% in omnivores. The intake is, consistent with the significantly lower vitamin B12 levels in the alternative diet group (187.7 vs. 283.4 pmol/l in children and 216.8 vs. 326.9 pmol/l in adolescents), with deficiency in 19% children and 32% adolescents vs. 0% omnivores (under 179 pmol/l). The RDA for folic acid are met by vegetarians, 262 and 170% vs. 140 and 106% in omnivores. Folic acid serum levels in vegetarians are significantly higher (24.4 vs. 18.23 nmol/l in children, 18,12 vs. 15.81 nmol/l in adolescents) with a 0% finding of deficient values vs. 5 and 11% in omnivores (less than 9.53 nmol/l). The results indicate unequivocally that for mild hyperhomocysteinaemia in alternative diets vitamin B12 deficiency is responsible.

        Key words: children, adolescents, vegetarians, omnivores, homocysteine, vitamin B12, folic acid