Routine Vitamin and Iron Biomarkers Do Not Explain Variation in Anti-Müllerian Hormone: Implications for Ovarian Reserve Testing in Clinical Practice

Background: Anti-Müllerian hormone (AMH) is a key biomarker of ovarian reserve, reflecting the quantity of the remaining follicular pool. While chronological age is the primary determinant of AMH concentrations, emerging evidence suggests that vitamin D, vitamin B12, folate, and iron metabolism parameters may also influence ovarian function through mechanisms involving steroidogenesis, DNA synthesis, and oxidative stress regulation. However, clinical findings regarding these associations remain inconsistent. Objective: The aim of this study was to evaluate the relationships between serum AMH concentrations and biomarkers of vitamin D status, vitamin B12, folate, ferritin, and lipid profile in women of reproductive age, and to compare the strength of these associations with that of chronological age. Methods: This retrospective, observational, cross-sectional study included 264 women who underwent AMH testing at Atlas University Hospital. Demographic and laboratory data including AMH, age, vitamin D, vitamin B12, folic acid, ferritin, and lipid parameters were extracted from electronic medical records. Bivariate correlations were assessed using Pearson’s and Spearman’s coefficients on both untransformed and Box–Cox power-transformed data, and were repeated as first-order partial correlations conditioning on chronological age. Statistical significance was set at p < 0.05. Results: The mean age was 34.61 ± 5.75 years, and median AMH was 0.96 ng/mL (Q1–Q3: 0.34–2.34). Age showed a moderate-to-strong, significant inverse correlation with AMH (Pearson’s r = −0.508, Spearman’s rho = −0.547; p < 0.001), and the linear component of this association strengthened after Box–Cox transformation (Pearson’s r = −0.553; p < 0.001). In contrast, vitamin D, vitamin B12, folic acid, ferritin, and lipid parameters (triglycerides, HDL, LDL, total cholesterol) showed no statistically significant and no clinically meaningful correlation with AMH, with all coefficients remaining below 0.20 regardless of transformation (all p > 0.05). After adjustment for age, every coefficient attenuated further towards the null (all |rpartial| < 0.10; all p ≥ 0.127), the largest being that of 25-hydroxyvitamin D (rpartial = 0.094, 95% CI −0.027 to 0.213). A sensitivity power analysis confirmed 80% power to detect an age-adjusted partial correlation of |r| = 0.172 and 91% power at |r| = 0.200. Conclusions: Age remains the principal determinant of ovarian reserve, while vitamin D, vitamin B12, folic acid, ferritin, and lipid parameters show no statistically significant or clinically meaningful association with AMH. These findings suggest that any biological influence of these micronutrients on ovarian reserve, if present, is markedly overshadowed by age-dependent follicular decline. Prospective studies incorporating longitudinal AMH measurements and standardized nutritional assessment are needed to further clarify these relationships.