Introduction: Bipolar disorder (BD) is associated with significant psychological and physical comorbidity, yet little is known about bone health. Interestingly, there is an increasing body of evidence to suggest that lithium, commonly used in the treatment of BD, may possess bone protective properties. To explore this further, we aimed to determine whether BD is associated with serum markers of bone turnover.
Method: Men and women with a history of BD (cases; n=116) were recruited from public and private health care settings and a sample of age-and sex-matched controls (3:1 ratio), without BD, were drawn from the Geelong Osteoporosis Study (n=348). BD was identified using a semi-structured clinical interview (SCID-I/NP). Blood samples were obtained and the bone resorption marker, C-telopeptide (CTx) and formation marker, type 1 procollagen amino-terminal-propeptide (PINP) were measured. Anthropometry and socio-economic status (SES) were determined and information on medication use and lifestyle was obtained via questionnaire. Multiple linear regression was used to determine the association between BD and bone turnover markers (CTx and PINP).
Results: Cases were heavier, more likely to smoke, be less active, have lower SES, were more likely to take bone active medications; otherwise the groups were similar. Adjusted mean CTx values were 5.7% lower [15.5 (95% CI 13.6–17.3) vs 16.4 (95% CI 14.6–18.2) pg/ml, p=0.03] and PINP values were 7.3% higher [6.3 (95% CI 5.6–6.9) vs 5.8 (95% CI 5.1–6.5) pg/ml, p=0.008] among the cases compared to controls. These relationships were independent of age, sex, weight, smoking, activity, alcohol and calcium consumption, SES and bone active medications. Following the removal of lithium users (n=47), these relationships were attenuated [CTx, p = 0.05; P1NP, p=0.09].
Conclusion: Our data suggests that lithium contributes to the observed differences in bone turnover observed between those with and without BD.