Comparison of Magnesium Status Using 24-h Urine Magnesium Content and Magnesium Fraction Excretion in PCOS with Non-PCOS Control Women: a Cross-sectional Study

**Background:** Polycystic ovarian syndrome (PCOS) is a common endocrine disorder affecting 5–10% of reproductive-age women, often associated with insulin resistance and metabolic disturbances. Magnesium (Mg), the second most abundant intracellular cation, is critical for enzyme function and insulin secretion. Previous studies comparing serum Mg levels between PCOS and control women have yielded conflicting results, with two 2020 systematic reviews and meta-analyses showing unexplained heterogeneity and contradictory conclusions. Since serum Mg represents only ~1% of total body Mg and may not accurately reflect Mg status, this study aimed to compare Mg status using 24-hour urinary Mg content and fractional excretion of magnesium (FEMg) in PCOS versus non-PCOS women.

**Methods:** This cross-sectional study was conducted at the Milad Infertility Clinic, Mashhad University of Medical Sciences, Iran, in 2021. Forty-four PCOS women (diagnosed by Rotterdam criteria) and 50 non-PCOS infertile controls were enrolled. Exclusion criteria included known endocrinopathies, chronic kidney disease, electrolyte abnormalities, pregnancy, breastfeeding, and use of Mg-based medications or diuretics. Participants underwent a 3-day washout of Mg-rich foods before providing a 24-hour urine sample and fasting blood sample. Main outcomes were 24-hour urinary Mg content and FEMg (calculated as [Mg(U) × Cr(S)] / [Mg(S) × Cr(U)] × 100). Other measurements included serum Mg, Ca, albumin, creatinine, potassium, 25-OH vitamin D, BMI, and blood pressure. Statistical analyses used independent t-test or Mann-Whitney test as appropriate, with P<0.05 considered significant. Sample size (44 per group) was calculated based on prior studies in type 2 diabetes, assuming effect size 31.0 mg/24h and SD 51.7 mg/24h, with 80% power and α=0.05.

**Key Results:** PCOS and control groups were age-matched (mean 30.86 vs. 33.06 years, P=0.07), but BMI was significantly higher in the PCOS group (28.49 vs. 24.93 kg/m², P=0.002). Mean 24-hour urinary Mg content did not differ significantly between PCOS and control groups (65.22 vs. 71.07 mg/24h, P=0.22). FEMg was also similar (2.661% vs. 2.881%, P=0.24). Serum Mg levels were comparable (2.47 vs. 2.41 mg/dL, P=0.17), as was the Ca/Mg ratio (3.55 vs. 3.64, P=0.26). Serum creatinine was slightly higher in PCOS (0.88 vs. 0.84 mg/dL, P=0.02), and serum potassium (4.12 vs. 3.98 mEq/dL, P=0.007) and albumin (4.60 vs. 4.50 g/dL, P=0.033) also differed, but these were not correlated with Mg measures. Vitamin D levels were similar (26.1 vs. 23.5 ng/mL, P=0.41). Clinical features: hirsutism (77% vs. 16%), acne (47% vs. 22%), acanthosis nigricans (31% vs. 0%), and menstrual disturbance (84% vs. 0%) were more prevalent in PCOS.

**Clinical Implications:** This study found no evidence of Mg deficiency in PCOS women compared to non-PCOS controls, using more reliable measures (24-hour urinary Mg and FEMg) than serum Mg alone. The findings contrast with some prior meta-analyses that suggested lower serum Mg in PCOS, but align with others that found no difference. The authors suggest that the heterogeneity in previous studies may stem from serum Mg's poor reflection of total body Mg status. They recommend using FEMg for future Mg status assessment. The lack of Mg deficiency implies that routine Mg supplementation may not be beneficial for infertile PCOS women. Limitations include the cross-sectional design, small sample size precluding adjustment for BMI as a confounder, and absence of dietary Mg intake data due to COVID-19 restrictions. All participants were infertile, which may limit generalizability. Future studies should include dietary assessment and larger samples.