Estrogen Contributes to Bone Renewal
The hormone estrogen has an important role in skeletal homeostasis (balance) with well recognized beneficial effects on bone mass. At the cellular level, estrogen effects both osteoclast and osteoblast function. Estrogen receptors are also located in the cortical outer layer and the trabecular inner layer of bone. An overview of these bone physiology terms is on the sidebar to the right of this page.
Estrogen contributes to inhibition of bone turnover and maintenance of the balance between bone resorption and formation. Estrogen also mediates indirect actions on bone through calcitonin and parathyroid hormone and through cytokines and growth factors. The postmenopausal loss of estrogen is associated with an increase in osteoclast production, and a decrease in osteoblast activity, which results in a decrease in bone density.
The most rapid loss of bone in women occurs within the first five years of menopause. Without preventive measures bone mass may be lost at an annual rate of 3% to 5% during the years directly after menopause. Eventually this rate slows down and continues at 1% to 2% a year. Regardless of the rate of bone loss, during ones sixties, seventies or eighties bone loss will occur without preventive measures.
During the accelerated period of bone loss immediately after menopause, trabecular bone loss increases threefold, while rates of cortical bone loss are slower. Factures of the wrist & spine are more frequent in the early postmenopausal years, with hip fractures tending to occur in the later years.
The extent of estrogen loss in postmenopausal women may pre-determine osteoporosis risk. The hormone estradiol is the predominant form of estrogen made by the body during a woman's reproductive years. Research indicates postmenopausal women with trace or undetectable blood levels of estradiol, (less than 5 pg per milliliter) have a greater risk of hip and vertebral fracture than postmenopausal women with detectable estradiol levels. A detectable concentration of estradiol in postmenopausal women is between 5-20 pg per milliliter.
In a study of 9704 women 65 years and older, that were observed for four to six years; women who had natural estrogen levels as low as five to ten *pg per milliliter, had a 62 percent lower risk of hip fractures and a 57 percent lower risk of vertebral fractures than women with estrogen levels less than 5 pg per milliliter. The findings of this study indicate that maintaining low levels of estrogen for postmenopausal women is osteoprotective.
Approximately 10 million American postmenopausal women have undetectable estradiol levels. This group of women is at risk for developing osteoporosis and bone fractures.
The risk of hip and vertebral fractures also increased as blood levels of sex hormone-binding globulin (SHBG) increased. Estrogen bound to SHBG is less available to the body to maintain bone mass. Researchers also found that blood levels of sex hormone-binding globulin, (a protein that carries estrogen in the blood), which were 1.0 ug per deciliter or higher were associated with a relative risk of 2.0 for hip fractures and 2.3 for vertebral fractures.
For women with both undetectable estrogen levels and sex hormone-binding globulin concentrations of 1.0 ug per deciliter the risk of hip fracture increased 14 fold and the risk of vertebral fracture increased 12 fold.
*picograms (pg) per milliliter (ml) estrogen levels.
For more educational information regarding low dose estrogen replacement for the maintenance of postmenopausal bone health click here.
Source:
Endogenous Hormones and the Risk of Hip and Vertebral Fractures among Older Women.
New England Journal of Medicine 1998; 339(11):733-738Cummings SR, Browner WS D
Source:
Menopause
Susan D. Reed MD., MPH and Elica L.Sutton, MD
Clinical Review ACP Medicine October 2004
ISSN:1547-1659