Directly measured free 25-hydroxy vitamin D levels show no evidence of vitamin D deficiency in young Swedish women with anorexia nervosa

Martin Carlsson, Lars Brudin, Pär Wanby

Anorexia nervosa (AN) is an eating disorder characterized by low fat mass complicated by osteoporosis. The role of circulating vitamin D in the development of bone loss in AN is unclear. Fat mass is known to be inversely associated with vitamin D levels measured as serum levels of total, protein-bound 25-hydroxyvitamin D, but the importance of directly measured, free levels of 25(OH)D has not been determined in AN. The aim of this study was to investigate vitamin D status, as assessed by serum concentrations of total and free serum 25(OH)D in patients with AN and healthy controls. In female AN patients (n = 20), and healthy female controls (n = 78), total 25(OH)D was measured by LC-MS/MS, and free 25(OH)D with ELISA. In patients with AN bone mineral density (BMD) was determined with DEXA. There were no differences between patients and controls in total or free S-25(OH)D levels (80 ± 31 vs 72 ± 18 nmol/L, and 6.5 ± 2.5 vs 5.6 ± 1.8 pg/ml, respectively), and no association to BMD was found. In the entire group of patients and controls, both vitamin D parameters correlated with BMI, leptin, and PTH. The current study did not demonstrate a vitamin D deficiency in patients with AN and our data does not support vitamin D deficiency as a contributing factor to bone loss in AN. Instead, we observed a trend toward higher vitamin D levels in AN subjects compared to controls. Measurement of free vitamin D levels did not contribute to additional information.