Background: Anorexia nervosa (AN) is a severe psychiatric disorder accompanied by multiple medical complications and significant mortality. Extremely low weight and continuous nutritional deficiencies might cause damage to the heart, hypoperistalsis, menstruation disorders, electrolyte disorders and bone loss - osteopenia, osteoporosis and increased incidence of bone fractures.
Recent studies demonstrated a harmful impact of low plasma sodium levels on bone mineral density (BMD). Damage to the bone was observed even with mild hyponatremia. In a cross-sectional study of adult women with AN, lower sodium level was associated with lower BMD, regardless of BMI, use of psychotropic drugs and disease duration. However, the association between sodium levels and BMD in adolescents with AN has not yet been evaluated.
Aim of our Study: To assess the correlation between hyponatremia and bone density in a large cohort of adolescent inpatients with AN.
Methods: Historic cohort study of 174 girls (aged 15.7 ± 1.8y) diagnosed with AN who were admitted to the psychosomatic department between 2003-2013. Demographic and clinical data, including age, comorbidity, use of psychotropic medications, anthropometric measurements, results of laboratory tests and bone mineral density (BMD) measurements were obtained from the patient’s medical charts.
Results: Mean lumbar spine BMD Z- score of the patients was lower than expected in the normal population (-1.5±1.2) and positively correlated with BMI-SDS (r=0.42, p<0.0001). Sixty-four girls (36.8%) had at least one hyponatremia episode during the year preceding the BMD study. Those girls had significantly lower lumbar spine BMD z-score (-1.8±1.2 vs. -1.3±1.2, p=0.01) compared to girls without hyponatremia. Lumbar spine BMD Z-score was also positively correlated with free T3 level (r=0.16, p=0.038), 17b-Estradiol (r=0.23, p=0.005) and LH (r=0.25, p=0.001); and negatively correlated with cortisol level (r=0.33, p<0.0001).
Conclusions: Hyponatremia is associated with decreased bone density in adolescents girls with AN. Additional studies are required to evaluate whether correction of hyponatremia will improve BMD.
