The calcium deficiency model for osteoporosis

Area of Science:

• Bone biology and metabolic diseases.

Background:

• Calcium deficiency causes osteoporosis in animals by prioritizing plasma calcium levels over bone health.
• Vitamin D deficiency leads to rickets and osteomalacia due to impaired calcium and phosphate homeostasis.
• Human osteoporosis, especially in postmenopausal women, is hypothesized to result from negative calcium balance.

Purpose of the Study:

• To evaluate the hypothesis that negative calcium balance contributes to human osteoporosis.
• To explore the role of urinary calcium loss and calcium absorption in osteoporotic women.

Main Methods:

• Review of existing data on calcium metabolism and osteoporosis.
• Analysis of factors influencing urinary calcium excretion, including plasma bicarbonate.
• Consideration of prospective trials with calcium supplementation and their conflicting results.

Main Results:

• In normal women, increased obligatory urinary calcium loss, potentially linked to higher plasma bicarbonate, is a key event.
• In osteoporotic women, elevated urinary calcium and malabsorption exacerbate bone resorption.
• Declining androgens may impair bone formation, adding to osteoporosis risk with age.

Conclusions:

• The calcium deficiency model for human osteoporosis is supported by the suppressibility of urinary hydroxyproline with calcium or calcitriol.
• Further clinical trials are necessary to definitively establish the validity of the calcium deficiency model in osteoporosis.