Low Sodium levels and Bone Loss in Anorexia Nervosa

The loss remained significant at all sites
for women with low sodium levels.

Severe bone loss is one of the serious side effects of anorexia nervosa (AN). Dr. Elizabeth A. Lawson and her colleagues at Massachusetts General Hospital reported that the severity of bone loss among a group of women with AN was associated with low plasma sodium levels (J Clin Psychiatry 2012; 73:1379).

In a cross-sectional study, the researchers evaluated bone loss in 404 women 17 to 54 years of age with Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) diagnoses of AN to prove their hypothesis that AN and relatively low plasma sodium levels would led to lower bone mineral density (BMD) than among women with higher plasma sodium levels. BMD was measured with dual-energy x-ray absorptiometry. The results were compared in women with plasma sodium levels < 140 mmol/L (the mid-point of the normal range), those with plasma sodium levels ≥140 mmol/L, and in women with hyponatremia (plasma sodium < 135 mmol/L) vs. those without hyponatremia.

Women with plasma sodium levels <140 mmol/L had significantly lower BMD t- and z-scores than did women with plasma sodium levels >140 mmol/L at the anterior-posterior spine (mean ± SEM z-scores= -2.2 vs. -1.5, respectively and total hip (mean ±SEM z scores = -2.5 vs. -1.0). In a model controlling for age, BMI, psychiatric drug use, and  disease duration,  differences between z- and t-scores remained significant at all sites.