V itamin 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 ( R 2  = .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.