Vegetarianism, vitamin B12 status, and insulin resistance in a group of predominantly overweight/obese South Asian women.

OBJECTIVES: Asian Indians are an at-risk group for vitamin B12 deficiency (because of vegetarianism) and insulin resistance (IR). Vegetarianism and consequent vitamin B12 deficiency may be associated with IR. This study aimed to describe the vitamin B12 status of predominantly overweight/obese women of South Asian origin living in Auckland and to correlate serum vitamin B12 and vegetarian status with IR as part of the larger Surya Study looking at health and lifestyle in this population.

METHODS: This was a cross-sectional study of 135 women at least 20 y of age who were not taking vitamin B supplements or medications that could affect vitamin B12 concentrations (serum vitamin B12 < 800 pmol/L). Data collection included serum vitamin B12, serum folate, measurements of IR (HOMA2-IR), and anthropometry. Vegetarian status was established for 124 subjects (90 non-vegetarians, 34 vegetarians).

RESULTS: Mean serum vitamin B12 was 227 pmol/L (95% confidence interval 210-245), serum folate was 19.1 nmol/L (18.0-20.2), and HOMA2-IR was 1.24 (1.13-1.36). Non-vegetarians had higher serum vitamin B12 levels (257 pmol/L, 235-281) than vegetarians (181 pmol/L, 159-207), P < 0.001. Vitamin B12 deficiency (<150 pmol/L) in vegetarians was 24% versus 9% in non-vegetarians. Non-vegetarians had increased body mass index (25.9 kg/m², 25.0-26.9, versus 23.9 kg/m², 22.6-25.3), waist circumference (81 ± 10.1 versus 75.8 ± 9.88 cm), and HOMA2-IR levels (1.30, 1.17-1.46, versus 1.00, 0.83-1.22). No correlation was found between serum vitamin B12 and HOMA2-IR. A significant positive correlation between non-vegetarian status and IR disappeared after controlling for body mass index.

CONCLUSIONS: This study population has a low serum vitamin B12 status, especially if vegetarian. The high rates of observed obesity may have overshadowed any other contributing factor to IR.