Vitamin D levels strongly influence bone mineral density and bone turnover markers during weight gain in female patients with anorexia nervosa.

OBJECTIVE: The aim of the study was to investigate a potential role for vitamin D status on bone mineral density (BMD) during weight gain in patients with anorexia nervosa (AN).

METHOD: Spine and hip BMD assessed by dual-energy X-ray absorptiometry (DXA), serum vitamin D (25-OH-D), N-propeptide of type I collagen (P1NP), C-terminal telopeptide of type I collagen (CTX), and intact parathyroid hormone (PTH) were measured before and after a 20-week intensive weight-restoration program in ninety-one female patients with AN and secondary amenorrhoea.

RESULTS: Ninety-one consecutive female patients (age 13-45 years; weight 39.4 ± 5.6 kg, body mass index [BMI] 15.1 ± 1.6 kg m-2 ) were included in the study. Although weight and BMI significantly increased in all patients during treatment, mean BMD only significantly increased at the spine (1.0% ± 3.6%, p = .009). The increase in spine BMD was significantly higher only above post-treatment 25-OH-D levels of 30 ng mL-1 (2.5% vs. 0.5%, respectively, for 25-OH-D ≥ and < 30 ng mL-1 , p = .026). There was a significant decrease in bone resorption (CTX; p = .043) and increased bone formation (P1NP; p < .001) after weight restoration. Nevertheless, a significant increase in PTH was also found, which was inversely correlated with decreased post-treatment 25-OH-D levels (R2  = .153, p < .001).

DISCUSSION: Hypovitaminosis D may counteract the efficacy of refeeding in AN through increased bone resorption mediated by secondary hyperparathyroidism, which strongly supports the use of vitamin D supplements for bone health in AN.