The Effect of a Selective Serotonin Reuptake Inhibitor on Gait, Balance, and Bone Metabolism in Older Adults

Selective serotonin reuptake inhibitors (SSRIs) are a class of antidepressant medication frequently used to treat depressive and anxiety disorders in the elderly. Although widely considered to be a safe option, several observational studies have found that SSRIs have as strong an association with falls as other psychotropic medications including tricyclic antidepressants and benzodiazepines. However, the potential mechanism for a link between SSRIs and falls is unclear. Compared to other psychotropic medications, SSRIs have lower rates of side effects that could contribute to falls, including sedation, orthostatic blood pressure changes, and anticholinergicity. Interestingly, SSRIs have also been associated with fractures, more so than other classes of antidepressants, in both administrative database studies and prospective cohort studies that control for falls history. Serotonin is known to play a role in regulating bone mass and some studies have found a loss of bone mass in individuals on SSRI treatment.

The association of SSRIs with falls and fractures is confounded by depression which is itself associated with falls, gait instability, bone loss and fractures. The goal of this study is to disentangle the contribution of the disease versus the treatment to risk of falls and fractures. As a first step towards this goal, this pilot study will: i) estimate effect sizes for statistical power calculations for an adequately powered study; and ii) examine the feasibility of timely recruitment of older patients with major depression who have not taken antidepressant medication for a minimum of 2 weeks prior to entering the study.

To address our research question, we have designed a prospective observational pilot study. Older adults with depression will be assessed at baseline, and then 3,6, and 12 weeks after initiation of sertraline antidepressant therapy. A non-depressed comparison group will be used to control for the learning effects of repeated assessment. The outcomes of interest are changes in gait, static balance, and dynamic balance recovery reactions. Our primary outcomes are the short-term changes in these variables at 3 weeks, but we will also perform a longitudinal analysis to assess change over 12 weeks.