Abstract
Bone health of the elderly is a major global health concern, since about 1 in 3 women and 1 in 5 men suffer from bone loss and fractures, often called osteoporosis, in old age. Bone health is a complex issue affected by multiple hormones and minerals. Among all the hormones involved in bone health, calcitriol (also vitamin D), parathyroid, and sex hormones (especially estrogen) have been discussed in this review paper. We have discussed the metabolism of these hormones and their effects on bone health. Vitamin D can be obtained from diet or formed from 7-dehydrocholesterol found under the skin in the presence of sunlight. The active form, calcitriol, causes dimerization of vitamin D receptor and acts on the bones, intestine, and kidney to regulate the level of calcium in blood. Similarly, parathyroid hormone is secreted when the serum level of calcium is low. It helps regulate the level of blood calcium through calcitriol. Sex hormones regulate bone modeling at an early age and remodeling later in life. Loss of ovarian function and a decrement in the level of production of estrogen are marked by bone loss in elderly women. In the elderly, various changes in the calcium and vitamin D metabolism, such as decrease in the production of vitamin D, decrease in dietary vitamin D, decreased renal production, increased production of excretory products, decrease in the level of VDR, and decreased calcium absorption by the intestines, can lead to bone loss. When the elderly are diagnosed with osteoporosis, medications that directly target bone such as bisphosphonates, RANK ligand inhibitors, estrogen and estrogen analogues, estrogen receptor modulators, and parathyroid hormone receptor agonists are used. Additionally, calcium and vitamin D supplements are prescribed.
Highlights
Bone is a very important organ that provides structural support and mobility and acts as a storehouse of the minerals such as calcium and phosphorous
Osteoclasts and osteoblasts act in the same space leading to renewal of bones without shifting in space. e remodeling process is active throughout the life in humans and is important for various reasons
During Journal of Osteoporosis the remodeling process, bone formation is almost inevitably followed by bone resorption [2]
Summary
Bone is a very important organ that provides structural support and mobility and acts as a storehouse of the minerals such as calcium and phosphorous. Osteoclasts and osteoblasts act in the same space leading to renewal of bones without shifting in space. E remodeling process is active throughout the life in humans and is important for various reasons It leads to repair of fractures and cracks that occur in the bones, renewal of old bone cells that could cause bone cells to become brittle, and release of calcium from bone tissues [1]. E step occurs mainly in the kidney, which involves the formation of 1,25 dihydroxy D3 (1,25(OH)2D3) from hydroxylation by 1 α-hydroxylase (CYP27B1) (Figure 2) Both 1,25(OH)2D3) and 25(OH)D3 are carried in the circulation by vitamin D binding protein. Before delving into detail about the different pathways dysregulated in vitamin D metabolism in the elderly, here are some of the immediate factors that could lead to vitamin D deficiency in the diet in the elderly: (a) lack of sunlight leading to lower vitamin D3 level, (b) avoidance of dairy vitamin D due to lactase deficiency, and (c) improper absorption of vitamin D from the intestines [10]
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