**Core Concept**
Glucocorticoids are a class of steroid hormones that play a crucial role in regulating various physiological processes, including bone metabolism. Long-term use of glucocorticoids is known to disrupt bone homeostasis, leading to an increased risk of osteoporosis.

**Why the Correct Answer is Right**
Glucocorticoids inhibit the activity of osteoblasts, cells responsible for bone formation, and promote the apoptosis of osteocytes, leading to a decrease in bone formation and an increase in bone resorption. This imbalance results in a net loss of bone mass and density, characteristic of osteoporosis. Additionally, glucocorticoids reduce the expression of osteocalcin, a protein essential for bone mineralization.

**Why Each Wrong Option is Incorrect**
**Option A:** Thiazide diuretics may actually increase bone density by reducing calcium excretion in the urine and promoting calcium absorption in the gut.
**Option B:** Bisphosphonates are actually used to treat osteoporosis by inhibiting bone resorption and promoting bone formation.
**Option C:** Loop diuretics can cause hypokalemia and hypomagnesemia, which may lead to secondary hyperparathyroidism, potentially exacerbating osteoporosis, but they are not the primary cause.

**Clinical Pearl / High-Yield Fact**
Glucocorticoids can cause osteoporosis even at relatively low doses, especially in patients with a history of prolonged glucocorticoid use or those with pre-existing bone disease. Monitoring bone density and implementing preventive measures, such as calcium and vitamin D supplementation, is essential in patients receiving long-term glucocorticoid therapy.

**Correct Answer: C. Glucocorticoids**