SEATTLE — Use of selective serotonin reuptake inhibitors is associated with bone loss comparable to that associated with glucocorticoid therapy, according to the findings of two studies.
In the first study (involving nearly 6,000 men), the mean bone mineral density (BMD) at the lumbar spine for the 158 participants using an SSRI at the time of a baseline dual energy x-ray absorptiometry scan was 4.6% lower than in nonusers, Elizabeth McKinstry Haney, M.D., said at the annual meeting of the American Society for Bone and Mineral Research.
By comparison, the 240 glucocorticoid users had a mean baseline BMD 2.9% lower than that of nonusers.
Relative to nonusers, mean total hip BMD was 3.9% lower in the SSRI users and 2.6% lower in the glucocorticoid users, relative to nonusers. At the femoral neck, mean BMD was 4.5% lower for the SSRI users and 2.2% lower for the glucocorticoid users.
Use of tricyclic antidepressants or trazodone was not associated with significantly different BMD findings, compared with nonusers, said Dr. Haney of Oregon Health Sciences University, Portland.
Another study presented at the meeting reported similar findings in women. That study looked at a cohort of 2,556 elderly women who were part of longitudinal investigation of fracture risk. The study compared bone mineral density measurements taken about 5 years apart. The rate of BMD loss among women who reported using an SSRI at the time of one or both of the bone density measurements was almost double that of women who were not taking an SSRI (0.81% vs. 0.47% per year), said Susan J. Diem, of the University of Minnesota, in a poster presentation.
Previous reports have suggested an association between SSRIs, bone loss, and fracture. However, it was unclear in those studies whether the SSRIs caused the bone loss or whether the bone loss was associated with depression, since the mood disorder itself has been tied to a number of factors that might lead to bone loss, such as altered cortisol levels and alcohol abuse, Dr. Haney said.
That is why Dr. Haney's study compared bone density in patients on SSRIs with patients taking other antidepressants.
The cause of the loss is probably related to osteoclasts' and osteoblasts' known expression of functional serotonin transporters, Dr. Haney suggested.
Studies that her group has conducted of SSRIs in mice have confirmed that SSRI treatment led to bone loss.
Dr. Haney said the strength of her study was that it collected very complete data, which permitted the researchers to control for everything from body mass to smoking and vitamin use in their analysis.
Still, the study was limited by the fact that SSRI dosages and duration of use were unknown.
“We don't rule out that other mechanisms might be involved as well, and that deserves further study” she said.