The status of plasma homocysteine and related B-vitamins in healthy young vegetarians and nonvegetarians

Eur J Nutr. 2003 Apr;42(2):84-90. doi: 10.1007/s00394-003-0387-5.


Background: Exclusion of animal products and having only plant protein in vegetarian diets may affect the status of certain B-vitamins, and further cause the elevation of plasma homocysteine concentration.

Aim: The purpose of this study was to assess the status of homocysteine and related B-vitamins in vegetarians and nonvegetarians. The effects of biochemical parameters of B-vitamins and dietary protein on plasma homocysteine were also examined.

Methods: The study was performed at the Chung Shan Medical University, Taichung, in the central part of Taiwan. Thirty-seven vegetarians (28.9 +/- 5.5 y) and 32 nonvegetarians (22.9 +/- 1.6 y) were recruited. Nutrient intake was recorded using 3-day dietary records. Fasting venous blood samples were obtained. Plasma homocysteine, folate and vitamin B-12 were measured. Vitamin B-6 status was assessed by direct measures [plasma pyridoxal 5'-phosphate (PLP) and urinary 4-pyridoxic acid (4-PA)] and indirect measures [erythrocyte alanine (EALT-AC) and aspartate (EAST-AC) aminotransaminase activity coefficient].

Results: There was no significant difference in vitamin B-6 intake between the two groups, although the vegetarian group had a significantly lower vitamin B-12 intake than the nonvegetarian group. Vegetarian subjects had significantly lower mean plasma PLP and vitamin B-12 concentrations than did nonvegetarian subjects (p < 0.05); however, a significantly higher mean plasma folate concentration was found in the vegetarian group. Vegetarian subjects had a significantly higher mean plasma homocysteine concentration than nonvegetarian subjects (13.2 +/- 7.9 vs. 9.8 +/- 2.2 micromol/L). Negative correlations were seen between plasma homocysteine and vitamin B-12 concentrations in the vegetarian (p = 0.004), nonvegetarian (p = 0.026), and pooled (p < 0.001) groups. From best subsets regression analyses, the plasma homocysteine concentration could be significantly predicted by total protein intake (p = 0.027) and plasma vitamin B-12 concentration (p = 0.005) in the pooled group. When the intake of protein is not considered, vitamin B-12 concentration is still a strong predictor of plasma homocysteine concentration (p = 0.012).

Conclusions: Vitamin B-12 intake and mean plasma vitamin B-12 concentration were lower for vegetarian subjects than for nonvegetarian subjects, leading to an increase in plasma homocysteine concentration. Vitamin B-6 and folate had little effect on plasma homocysteine concentration when individuals had adequate vitamin B-6 and folate status.

MeSH terms

  • Adult
  • Diet, Vegetarian / statistics & numerical data*
  • Dietary Proteins / metabolism
  • Female
  • Folic Acid / blood
  • Homocysteine / blood*
  • Humans
  • Male
  • Nutritional Status / physiology*
  • Reference Values
  • Regression Analysis
  • Vitamin B 12 / blood*
  • Vitamin B 6 / blood*
  • Vitamin B 6 / urine


  • Dietary Proteins
  • Homocysteine
  • Vitamin B 6
  • Folic Acid
  • Vitamin B 12