Serum 25-Hydroxyvitamin D Concentrations and Cardiometabolic Health Across Pregnancy: Associations with Glucose Homeostasis, Cholesterol, and Abdominal Adiposity

This cohort study aims to document longitudinal and trimester-specific associations between serum 25(OH)D concentrations ([25(OH)D]) and cardiometabolic markers and gestational weight gain. Participants (n=79) underwent fasting blood sampling each trimester and a 2-hour 75g oral glucose tolerance test (OGTT) in the first and second trimesters. Serum [25(OH)D] was measured by LC-MS/MS. Glucose and insulin were measured enzymatically or by electrochemiluminescence to calculate glycemic indices. Lipids were measured enzymatically. Subcutaneous (SAT) and visceral (VAT) abdominal adipose tissue thickness was measured by ultrasound. In longitudinal mixed models, each 10nmol/L increase in [25(OH)D] was associated with lower fasting insulin (β=-8.0pmol/L, 95% CI: -14.5, -1.5; p<0.05), higher HOMA-IS (β=0.01, 95% CI: 0.002, 0.018; p=0.01), and higher fasting total cholesterol (β=0.06mmol/L, 95% CI: 0.01, 0.11; p<0.05) across pregnancy, after adjustment for season, age, parity and pre-pregnancy BMI. Unadjusted trimester-specific analyses indicated that in the first trimester, each 10 nmol/L increase in [25(OH)D] was associated with thinner SAT (β=-1.5mm, 95% CI: -2.4, -0.1; p<0.01) and VAT (β=-2.4mm, 95% CI: -4.0, -0.1; p<0.01). No association was found with gestational weight gain. In the first trimester, participants with [25(OH)D] below the clinical sufficiency threshold of 50 nmol/L had higher fasting insulin, lower insulin sensitivity, and thicker SAT (p<0.05), after adjustment for age and parity. In conclusion, higher serum [25(OH)D] were associated with more favorable cardiometabolic profiles during pregnancy, especially glucose regulation and abdominal adiposity. These findings suggest that maintaining an adequate vitamin D status is associated with better cardiometabolic health during pregnancy, although causality cannot be inferred.