Low Plasma Sodium and Bone Loss in Women with Anorexia Nervosa

Plasma sodium deficiency may
worsen osteopenia in AN patients.

Dr. J. G. Verbalis and colleagues at Georgetown University, Washington, DC, were the first to report that chronically low levels of sodium can lead to a substantial reduction of bone mass (J Bone Miner Res 2010; 25: 554). Those authors also noted that their study results suggest that bone quality should be assessed in all patients with chronic hyponatremia.

Researchers at Massachusetts General Hospital, Boston, recently found that relative sodium deficiency may be a contributor to development of AN-related osteopenia (J Clin Psychiatry 2012; 73:e1379). Dr. Elizabeth A. Lawson and co-workers conducted a cross-sectional study of 404 women 17 to 54 years of age (mean age: 25.6 years) with DSM-IV criteria for AN. The researchers measured bone mineral density (BMD) using dual-energy x-ray absorptiometry. Then, BMD was compared in women with plasma sodium levels lower than 140 mmol/L (the mid-point of the normal range) versus those with plasma sodium levels ≥140 mmol/L and those with hyponatremias or plasma sodium levels <135 mmol/L.

Women with plasma sodium levels <140 mmol/L had significantly lower BMD and t and z scores at the anterior-posterior spine and total hip compared to women whose plasma sodium levels were greater than 140 mmol/L. And, in a model controlled for age, body mass index, psychiatric drug use and disease duration, differences in BMD and z and t scores remained significant at all sites. The authors concluded that relative plasma sodium deficiency may contribute to AN-related osteopenia.