Corticosteroids are one type of steroid medication. Sometimes the term "steroid" is used interchangeably with "corticosteroid".
According to the ACR, more than 30 million Americans may be affected by diseases commonly treated with corticosteroids. Steroids such as prednisone, are used as therapy for many inflammatory and autoimmune diseases, such as:
Corticosteroids & Bone Remodeling
Corticosteroids affect calcium and bone metabolism in many ways.
- steroids decrease the amount of calcium absorbed by the intestine
- steroids increase calcium excretion through the kidneys
These two factors combine to produce a decline in the circulating ionized calcium concentration. This triggers the parathyroid glands to increase the secretion of parathyroid hormone (PTH), a condition known as secondary hyperparathyroidism. Elevated PTH levels result in increased bone breakdown, as the body attempts to rectify low circulating calcium levels by releasing calcium from the bones into the blood.
Corticosteroids can also decrease the levels of the sex hormones:
- estrogen (in women)
- testosterone (in men)
The resulting decreases are associated with increased bone loss.
Corticosteroids also cause muscle weakness, which may lead to inactivity and additional bone loss. Another major effect of corticosteroids is that they can impact bone directly by suppressing bone formation (osteoblastic) activity.
Patterns of Bone Loss
There are two types of bone tissue: cortical and trabecular.
- Cortical bone forms the outer shell of bone and comprises 80% of the skeleton
- Trabecular bone (the remaining 20%) is found inside the bone
Each bone in the skeleton contains both types of bone, but their proportions vary. Corticosteroids primarily cause bone loss in those areas of the skeleton that are rich in trabecular bone, such as the spine.
Dose and Duration
Bone loss occurs most rapidly in the first 6 to 12 months of therapy and is dependent on both:
Other risk factors for osteoporosis may have an additive effect on bone loss, such as:
- underlying disease
For example, elderly men on steroids may experience even greater bone loss and risk for fracture than middle aged men. ACR estimates that without prevention measures, an estimated 25% of individuals on long-term corticosteroids will experience a fracture.
The dose of corticosteroids is a strong predictor of fracture risk. While it is not clear whether there is a low-dose threshold below which bone loss does not occur, recent studies have found inhaled steroids to have little to no effect on bone density when administered in standard doses and apart from systemic steroids.
Steroid-induced osteoporosis is both preventable and treatable. According to ACR, people on corticosteroids should have a bone mineral density test performed. This test will provide a baseline measurement from which to monitor subsequent changes in bone mass. ACR also recommends a daily intake of 1500 mg. calcium and 400-800 IU of vitamin D. Calcium and vitamin D can help maintain calcium balance and normal parathyroid hormone levels, and can even preserve bone mass in some patients on low-dose steroid therapy.
Osteoporosis medications approved by the FDA for corticosteroid-induced osteoporosis include:
In corticosteroid users, both drugs deliver beneficial effects on spine and hip bone mineral density and are associated with a decrease in spinal fractures. Estrogen therapy and Miacalcin (Calcitonin) may help preserve spinal bone mass in postmenopausal women on corticosteroids, but neither is FDA approved for corticosteroid-induced osteoporosis.
- Eliminating smoking and alcohol, are important in reducing the risk of steroid-induced osteoporosis.
- Physical activity and exercise can help to preserve bone and muscle mass, while increasing muscle strength and reducing the risk of falls.
- Slip and fall prevention is of particular significance for elderly individuals and for those who have experienced steroid-induced muscle weakness.
The Bottom Line
Osteoporosis prevention measures should begin early, ideally at the onset of corticosteroid therapy. Experts recommend using the lowest dose of steroid for the shortest period of time possible and, when feasible, inhaled or topical corticosteroids should be utilized.
Source: Glucocorticoid-Induced Osteoporosis, NIH ORBD~NRC, 12/2000