Osteoporosis, an age related disease of skeletal system, may occue due to

Options

A. immune disorder affecting neuromouscular junction leading to fatigue.
B. high concetration of `Ca^(++)` and `Na^(+)`
C. decreased level of estrogen
D. accumulation of uric acid leading to inflammation of joints

Answer

**Step-by-Step Solution:**

1. **Understanding Osteoporosis**:
- Osteoporosis is characterized by low bone mass and loss of bone tissue, leading to weak and fragile bones. It occurs due to an imbalance between new bone formation and old bone resorption.

2. **Identifying Causes**:
- The question asks for the reasons that may lead to osteoporosis. The options provided include:
- A) Immune disorder affecting neuromuscular junction leading to fatigue.
- B) High concentration of calcium and sodium ions.
- C) Decreased level of estrogen.
- D) Accumulation of uric acid leading to inflammation of joints.

3. **Analyzing Each Option**:
- **Option A**: Immune disorder affecting the neuromuscular junction (e.g., myasthenia gravis) does not relate to bone mass or osteoporosis. Thus, this option is incorrect.
- **Option B**: High concentration of calcium and sodium ions is not a cause of osteoporosis. In fact, osteoporosis is associated with low calcium levels in bones. Therefore, this option is also incorrect.
- **Option C**: Decreased level of estrogen is a significant factor leading to osteoporosis, especially in postmenopausal women. Estrogen is crucial for maintaining bone density, and its deficiency can lead to increased bone resorption and decreased bone formation. This option is correct.
- **Option D**: Accumulation of uric acid leading to inflammation of joints is related to gout, not osteoporosis. Therefore, this option is incorrect.

4. **Conclusion**:
- The correct answer is **C) Decreased level of estrogen**, as it is a well-established cause of osteoporosis, particularly in older women.