introduction
Osteoporosis is a skeletal condition characterized by development of fragile bones with an increased tendency to fractures. It occurs in all age groups but with an increased tendency in later life. Prevalence, according to the NIH, is more among the elderly, with women far more affected than men.
One of the preventive approaches in those susceptible to osteoporosis is HRT, or hormone replacement therapy. Hormone replacement therapy is the prescription of estrogen alone or in combination with progesterone in postmenopausal women to treat some of the symptoms of menopause. It has been found to positively affect bone health in menopausal women, with an increase in bone density with significantly reduced incidence of osteoporosis and pathological fractures in women receiving the treatment over those not receiving the treatment.
Sex Hormones in Bone Health
Human bone formation is under the influence of diverse factors that change with advancing age. New bone is laid down by a specialized group of cells called osteoblasts. These cells, under the influence of growth hormone at first followed by sex hormones in later life, lay down collagen fibers that act as scaffolding. These fibers are later overlaid with complex calcium compounds to form rods and plates that make up the bones. Another set of cells called osteoclasts are charged with removing older deposits of bone so that there is a constant renewal of bones for optimal function. New bone formation goes on at the same time with old bone breakdown or resorption. Estrogen appears to promote new bone formation and inhibit resorption of old bone. Estrogen also promotes the absorption of calcium in the intestines and reduces the loss of calcium in the urine.
In the very young, new bone formation is ahead of resorption of old bone, with the net result of growth and increasing density of bone. At puberty, there is a growth spurt that indicates the start of the influence of estrogen in women and testosterone in men on the process of bone formation. About the age of 20 years and after, there is a balance between new bone formation and resorption of old bone, with cessation of growth and maintenance of a constant bone density and strength. At menopause, with the drop in estrogen levels, resorption of bone overtakes new bone formation with a resultant thinning and weakness of bone. This leads to easy breaking of bones called pathological fractures. These fractures usually occur in the wrists, hips or spine-areas used for weight bearing.
HRT in Osteoporosis
The administration of estrogen to a menopausal woman restores the balance of bone formation by the stimulation of osteoblasts to produce new bone and the reduction in the activity of osteoclasts with reduced bone resorption. Increased absorption of calcium and vitamin D in the intestines with reduced losses of calcium in the urine by estrogen also have a positive impact on preventing the development of osteoporosis in those receiving HRT. The Surgeon General's report cites several studies that have proved the efficacy of hormone replacement therapy as a preventive measure in osteoporosis. There is also ample documentation that patients with osteoporosis on estrogen (HRT) actually begin to recover normal bone density with increased formation of new bone. The rate of pathological fractures, as a sign of on-going thinning of bony plates, is also reduced with HRT.
