"What is interesting about this study is that we took age out of the equation," principal investigator Jane Lukacs said. She is a Pfizer post-doctoral fellow and assistant research scientist at the U-M School of Nursing. Lukacs will present her findings at ENDO 2003, the Endocrine Society's annual meeting in Philadelphia June 19-22.
Studies involving hormone replacement therapy have found improvement in bone density of post-menopausal women, leading experts to infer that estrogen withdrawal at menopause is a major risk factor for osteoporosis. The question of whether the natural decline of estrogen after menopause causes bone loss has not been definitively shown.
After Lukacs and her research team found that aging-related bone loss has only a minor influence on bone function as compared to the body's natural estrogen withdrawal, which affects a number of parameters of bone health, Lukacs concluded: "Therapy should be different at different points in a woman's life."
The U-M team studied a group of women aged 20-52, and age-matched women who had and had not gone through menopause for study purposes---for example, she examined a 47-year-old woman still having regular menstrual cycles and compared her data to a 47-year-old woman who had not had regular cycles for 12 months.
She excluded women who used any form of hormones or regular prescription medication, and also eliminated smokers and heavy drinkers. Study subjects were neither, as Lukacs describes them, endurance athletes or couch potatoes.
Typically the rate of bone turnover---that is, the rate at which the body replaces old bone material with new---accelerates as women reach menopause. Because the replacement of old bone with new bone is not as efficient in menopause, a faster rate of turnover should translate to bone loss. This study examined bone biomarkers in the different groups of women to see when bone turnover increases and if measured calcium in the blood would be elevated, suggesting greater mineral loss from bones.
Most preventive bone therapies, given in the hope of protecting women against osteoporosis, slow the rate of bone turnover. But Lukacs' numbers showed pre-menopausal women did not have elevated bone turnover as they aged. "Why would you want to slow a rate of bone turnover that's normal?" Lukacs asked.
Thus, with women already nervous about hormone replacement therapy, this study gives further reason to be cautious about overprescribing hormone therapy or other conventional therapies used to slow bone turnover when it might be unnecessary in middle-aged women who still have regular menstrual cycles. Studies have shown a possible connection between HRT and cancer, as well as dementia.
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A two-year, $130,000 fellowship from Pfizer helped fund Lukacs' research.
U-M School of Nursing: http://www.nursing.umich.edu/
Endocrine Society: http://www.endo-society.org/
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