Vegetarian versus Non-Vegetarian Differences in Serum Vitamin D3, Vitamin B12, Thyroid Profile and Glycemic Status (HbA1c) in an Indian Population: A Cross-Sectional Analytical Study

Background: Dietary pattern is an important, modifiable determinant of micronutrient status and may plausibly influence Vitamin D, Vitamin B12 and glycaemic control. Indian data that simultaneously examine these biomarkers, alongside thyroid function, according to dietary habits remain limited. The objective is to compare serum Vitamin D3, Vitamin B12, thyroid profile (FT3, FT4, TSH) and HbA1c between vegetarian and non-vegetarian adults attending a single center in India, and to examine the demographic correlates of these biomarkers. Material and Methods: This retrospective cross-sectional study was carried out among 200 patients attending Government Medical College Hospital, Dungarpur [Shree Haridev Joshi Hospital] undergoing routine laboratory investigation, classified as vegetarian (n = 125) or non-vegetarian (n = 75) by self-reported dietary habit. Serum Vitamin D3, Vitamin B12, FT3, FT4, TSH and HbA1c were measured by standard laboratory methods. Between-group comparisons used Welch's independent-samples t-test with Cohen's d as the effect-size estimate; categorical variables (sex, Vitamin D deficiency, Vitamin B12 deficiency, glycaemic control) were compared using the chi-square test, and Pearson correlation was used to explore associations between age and biomarker concentrations. A two-sided p-value < 0.05 was considered statistically significant. Results: Vegetarians were, on average, older than non-vegetarians (50.9 ± 16.5 vs 45.0 ± 17.2 years; p = 0.018). Mean Vitamin D3 was comparable between groups (19.48 ± 10.67 vs 18.80 ± 9.08 ng/mL; p = 0.632), as was HbA1c (6.50 ± 2.14% vs 6.51 ± 1.85%; p = 0.969). Vitamin B12 was numerically higher among non-vegetarians (468.19 ± 496.98 vs 358.84 ± 399.17 pg/mL; p = 0.108, Cohen's d = -0.25), a small-to-moderate but statistically non-significant effect. Thyroid parameters (FT3, FT4, TSH) did not differ significantly between groups, although FT3 showed a borderline trend (p = 0.091). Vitamin D deficiency (<30 ng/mL) was strikingly common in both groups (88.5% overall; 88.0% vegetarian vs 89.3% non-vegetarian, p = 0.954), and Vitamin B12 deficiency (<200 pg/mL) was present in 35.0% of the cohort with no significant between-group difference (p = 0.146). Age correlated positively with Vitamin B12 (r = 0.220, p = 0.002) and HbA1c (r = 0.215, p = 0.002), but not with Vitamin D3 (r = 0.103, p = 0.147). Conclusion: Vegetarian and non-vegetarian adults in this cohort demonstrated comparable Vitamin D3, thyroid profile and HbA1c levels. Vitamin B12 concentrations trended higher in non-vegetarians without reaching conventional statistical significance, and the near-ubiquitous prevalence of Vitamin D deficiency across both dietary groups suggests that dietary pattern alone does not adequately explain the burden of hypovitaminosis D in this population. Age emerged as a relevant correlate of Vitamin B12 and glycaemic status and merits consideration as a covariate in future, larger studies.

Keywords: Vegetarian, Non-vegetarian, Vitamin D3, Vitamin B12, HbA1c, Thyroid function, Glycaemic status, India, Cross-sectional study.