There is some evidence that antidepressants, particularly the serotonin reuptake inhibitors, can reduce bone density, and increase the risk of fractures. This risk would be most pertinent in an elderly population.
Serotonin is a relevant factor in bone metabolism, so it is important to consider the potential impact of serotonergic antidepressants on bone health.
Here's a study showing an association between depression and reduced bone mineral density. Depression itself is an understandable cause for bone mineral loss, since it is associated with fatigue, therefore less exercise, worse nutrition, and increased stress hormones such as corticosteroids. In this study, antidepressant use was independently associated with bone mineral density loss in women. It is a retrospective analysis from a large catchment area study involving over 1000 people, who were followed since 1981.
There are some other studies showing an association between antidepressant use (especially SSRIs) and fractures due to fragile bone. One of the better such studies was published in 2008, looking at the incidence of fractures in a large population-based cohort involving 7983 people aged 55 and over. Importantly, the authors attempted to control for the impact of depression itself on fracture incidence, and basically showed that current SSRI use approximately doubles the risk of fractures:
There is one important prospective animal study, which shows a small effect of SSRI treatment on bone quality over a 6-month period:
In conclusion, it is important to know that antidepressants could possibly reduce bone density, and therefore contribute to an increased risk of fractures in the elderly. If antidepressant therapy is needed, it is especially important to encourage activities which protect bone health, such as regular exercise, and good nutrition (including ample calcium and vitamin D in the diet). Non-SSRI antidepressants such as tricyclics may have a smaller effect than the SSRIs. Bone density testing could be indicated, as could medication treatments to protect bone mineralization. These issues should be discussed with your family physician and your psychiatrist.