Aim: Bipolar disorder is associated with significant psychological and physical comorbidity. Yet little is known about the bone health of adults with bipolar disorder. Thus, we aimed to investigate the association between bipolar disorder and bone mineral density (BMD) in women.
Method: Women with a history of bipolar disorder (n=117) were recruited from the Barwon Statistical Division. Controls, without bipolar disorder, were drawn from the Geelong Osteoporosis Study (n=909). Bipolar disorder was identified using a semi-structured clinical interview (SCID-I/NP). BMD (g/cm2) was measured at the PA-spine, hip and total body using DXA (Lunar). Weight and height were determined and information on medication use and lifestyle variables were obtained via questionnaire. Linear regression models were used to test associations, after adjusting for age and weight.
Results: Cases were heavier (p=0.003), less active (p=0.001), more likely to smoke (p=0.003), take psychotropic medication (p=<0.001) and have lower BMD at the total hip (p=0.03); otherwise the groups were similar in age, height and spine and total body BMD. After adjustments, mean BMD among the cases was 4.7% lower at the hip [0.944 (95%CI 0.923-0.966) vs 0.991 (95%CI 0.983-0.999), p=<0.001] and 1.3% lower at the total body [1.154 (95%CI 1.141-1.168) vs 1.169 (95%CI 1.164, 1.174), p=0.05] compared to controls. Age was an effect modifier at the spine. Among women <50yr (n=553), mean spine BMD for cases was 3.1% lower [1.233 (95%CI 1.197-1.269) vs 1.272 (95%CI 1.259-1.285), p=0.05]. No differences in spine BMD for those ≥50yr were detected. These associations persisted after further adjustment for smoking, physical activity and psychotropic medications.
Conclusion: These population-based data suggest bipolar disorder is associated with reduced BMD in women. Given the dearth of literature, replication and research into underlying mechanisms are warranted.