Rate of Bone Loss During Menopause

It has been well established that the most important risk factor for bone loss for women in mid-life is menopause. Women lose approximately 50 percent of their trabecular bone and 30 percent of their cortical bone over the course of a lifetime – about half is lost during the first 10 years after menses have ceased.

Anatomy Basics

Trabecular bone: Spongy tissue that fills the inner cavity of long bones.

Cortical bone: Dense, extremely hard tissue that forms the surface of bones.

What Problem Was Studied?

The Study of Women’s Health Across the Nation (SWAN) is a seven-center study of the menopause transition in a sample of women from multiple ethnic groups. MaryFran R. Sowers, PhD, of University of Michigan at Ann Arbor, is a past recipient of an Arthritis Foundation research grant, one of the principal investigators in SWAN and chair of the SWAN Bone Committee. One goal of this study is to determine when bone loss begins and at what rate women lose bone during the various stages of the menopause transition. Because this is a multi-ethnic cohort – including women of Caucasian, African American, Chinese and Japanese background – ethnic differences in bone loss are also able to be identified.

What Was Done in the Study?

Of the women enrolled in SWAN, 1,902 had baseline bone mineral density (BMD) measurements and results of at least one follow-up exam available for analysis. At each annual visit, menopause stage was determined, BMD was measured, factors possibly related to BMD were assessed (such as calcium intake, cigarette smoking, etc.) and height and weight were measured. A woman was classified as premenopausal if she had experienced at least one menstrual period in the last three months with no change in menstrual regularity during the past year. Early perimenopausal was defined as having at least one period in the last three months with some change in menstrual regularity during the past year. Late perimenopause was defined as no menstrual bleeding in the last three months but some bleeding during the last 11 months. Postmenopause was established once a woman had gone 12 consecutive months without a menstrual period.

What Were the Study Results?

Body weight and ethnicity were powerful predictors of baseline BMD in this study, so the research team performed additional analyses to separate out these elements. The research team found that BMD began to decline substantially during late perimenopause and continued to decline rapidly during early postmenopause. The women with the lowest body weight lost bone considerably faster than women with the highest body weight.

Of importance, initial data analysis appeared to reveal an ethnic difference in rates of BMD loss. However, once the team accounted for those differences in body weight across the race/ethnic group, the ethnic disparity disappeared. Ethnicity did not predict bone loss rate once body weight was taken into account.

What Does This Mean for Women in Mid-Life?

Because there is little if any change in BMD in premenopause or in early perimenopause, there is no need to have bone density screened at that point in your life, unless you have independent risk factors for low bone mass or bone loss, including family history of osteoporosis, treatment with chemotherapy or surgery to remove the ovaries. The authors conclude that screening for osteoporosis should be considered at the late stage of the menopause transition (once you’ve missed three consecutive menstrual periods), particularly if you have a body mass index less than 22 kg/m2.

Finkelstein JS, Brockwell SE, Mehta V, et al. Bone mineral density changes during the menopause transition in a multi-ethnic cohort of women. J Clin Endocrinol Metab. December 26, 2007. Epub ahead of print.

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