Vitamin D and Osteoporosis

Osteoporosis is a bone disease characterized by a decrease in bone mineral density and the appearance of small holes in bones due to loss of minerals.¹ Vitamin D is an important factor in maintaining bone health to avoid osteoporosis.² Precise maintenance of the physiologic levels of both extracellular and intracellular ionized calcium is essential to life.³ The vitamin D metabolite 1,25-dihydroxyvitamin D (1,25-D) maintains calcium homeostasis between blood, cells and bones by stimulating calcium absorption from the intestines, reabsorption in the kidneys, and resorption in bones. 1,25-D up-regulates vitamin D receptors (VDR) in the small intestine, which then transcribes genes that shuttle calcium and phosphorus through the intestinal epithelium. However, mucosal response and calcium/phosphorus absorption is dependent on a competent VDR and elevated 1,25-D reduces VDR competence.⁴ Thus, calcium and phosphorus absorption may be inhibited if VDR function is impaired by elevated 1,25-D.

Although some studies show vitamin D and calcium supplements increase bone density slightly and decrease the risk of falls and fractures in certain populations, the quality of evidence is poor.⁵ A 2013 report by the U.S. Preventive Services Task Force recommends against vitamin D supplementation for the primary prevention of fractures in non-institutionalized, pre or post-menopausal women or older men.⁶ The 2005 RECORD study concluded, "...routine supplementation with calcium and vitamin D3, either alone or in combination, is not effective in the prevention of further fractures in people who had a recent low-trauma fracture." ⁷ A similar study stated, "We found no evidence that calcium and vitamin D supplementation reduces the risk of clinical fractures in women with one or more risk factors for hip fracture." ⁸ A 2008 study found, "Vitamin D supplementation adds no extra short-term skeletal benefit to calcium citrate supplementation even in women with vitamin D insufficiency." ⁹ And a study at the Bone Mineral Research Center, Winthrop University Hospital, Mineola, NY showed that "Additional intake of 100 mcg vitamin D3 did not lower PTH or markers of bone turnover." ¹⁰

In fact, there is ample evidence that elevated 1,25-D leads to bone loss. In 1999, Brot et al found "...elevated levels of 1,25-D were strongly associated with decreased bone mineral density and content, and increased bone turnover." ¹¹ "When levels are above 42 pg/ml 1,25-D stimulates bone osteoclasts. This leads to osteoporosis, dental fractures and calcium deposition into the soft tissues: lungs, breasts, muscle bundles, kidneys." ¹² An earlier study warned, "Vitamin D is a toxic compound, and excessive amounts can cause soft-tissue calcification. There is a narrow leeway between the amount required and that initiating tissue damage." ¹³ Kawamori et al found that, "Elevated 1,25-D induces increased production of osteoclasts from stem cells." ¹⁴ And the EMAS study found that "A combination of high 1,25-D and low 25-D is associated with the poorest bone health." ¹⁵ This significant evidence regarding bone loss should motivate medical practitioners and researchers to measure both 25-D and 1,25-D to determine vitamin D status. 
 
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