Aim: Psychiatric disorders and most medications used to treat them have been previously shown to be independently associated with skeletal deficits. In contrast, there is increasing evidence suggesting lithium may possess skeletal protective properties. Thus, we aimed to investigate the association between lithium use and bone mineral density (BMD) in a sample of women with bipolar disorder.
Method: Women with a history of bipolar disorder (n=117) were recruited from the Barwon Statistical Division, south-eastern Australia. Bipolar disorder was confirmed using a semi-structured clinical interview (SCID-I/NP). BMD (g/cm2) was measured at the spine, hip and total body using dual-energy X-ray absorptiometry (Lunar). Weight and height were measured and information on medication use and lifestyle variables were obtained via questionnaire. Socioeconomic status (SES) was determined. Linear regression models were used to test associations between lithium use and BMD, after adjusting for age, weight and medication known to affect bone.
Results: Thirty five (29.9%) women reported current lithium use. Lithium users and non-users differed in regards to SES (p=0.03) and BMD at the hip (p=0.03); otherwise the groups were similar in age, weight, height, smoking status, activity levels, alcohol and calcium intake and BMD at the spine and total body. After adjustments, mean BMD among lithium users was 5.0% greater at the spine [1.275 (95% CI 1.229-1.321) vs 1.214 (95% CI 1.183-1.244) g/cm2, p=0.03], 4.2% greater at the hip [0.979 (95%CI 0.942-1.016) vs 0.938 (95%CI 0.910-0.966) g/cm2, p=0.03] and 2.2% greater at the total body [1.176 (95% CI 1.148-1.205) vs 1.150 (95%CI 1.129-1.171) g/cm2, p=0.08] compared to non-users. Smoking, physical activity, alcohol and calcium intake, SES and other psychotropic medications did not contribute to the models.
Conclusion: These data suggest lithium use is associated with greater BMD in women with bipolar disorder. Replication and research into underlying mechanisms are warranted.