MODULE SUPPLEMENT: MUSCULO-SKELETAL SYSTEM
Many Factors Influence Bone Health

1,25-Dihydroxyvit D3 profoundly influences Osteoblast function through control of gene expression; it also can recruit Osteocytes and is an inducer of resorption. More data are supporting the use of Vitamin D in the prevention and treatment of osteoporosis.

Estrogen enhances bone formation and significant bone loss occurs during pre and immediately after menopause when estrogen levels decline. Testosterone also influences bone health but its decline in men is usually less precipitous.

Glucocorticoids decrease procollagen type I mRNA levels and thus exert profound effects on Osteoblast function. This is why we have to monitor bone health and initiate preventive or protective treatment soon after the initiation of glucocorticoid therapy.

T3 induces differentiation of osteoblast cells but, in higher amounts, can also recruit osteoclasts which negatively affects bone mass. This is why hyperthyroidism or over treatment of hypothyroidism can cause bone loss and osteoporosis.

Growth Hormone stimulates Insulin Like Growth Factor I (IGF-I). Although growth hormone has a positive effect on bone and lean body mass, its use is limited by its other physiologic effects. Also see the discussion of Growth Hormone in the Endocrine System Module Supplement (Note: This link will open in a new browser window which you can close to return here).

Calcitonin is considered a neuropeptide because the parafollicular C cells of thyroid are derived from the neural crest. Calcitonin inhibits osteoclastic bone resorption and is one of the medications often used to treat osteoporosis.

The Sympathetic Nervous System can also have a direct but local effect on bone health. In addition, it is increasingly recognized that many local factors influence bone health. However, whether they change with age and how they influence age related bone loss have not yet been well studied.

Other factors influencing bone health include, Calcium balance, physical activity, fat mass (which produces estradiol), and other life style factors. Calcium absorption tends to decline with age, especially in women. Thus it's recommended that women get at least 1500mg of Calcium if they are post-menopausal. Exercise is needed because weight bearing is essential to maintenance bone density.