Major Finding: The annual rate of bone loss during the late perimenopausal and early postmenopausal years is 1.8%–2.3% in the lumbar spine and 1.0%–1.4% in the hip. At those rates, 5 years of bone loss would translate to a 7%–10% drop in BMD at the spine in the average woman, along with a 5%–7% decline at the hip.
Data Source: SWAN, a long-term, longitudinal, observational study of 3,302 women from five ethnic groups at seven U.S. sites who were pre- or early perimenopausal at enrollment.
Disclosures: Dr. Santoro declared having no financial interests relevant to the National Institutes of Health–funded study.
DENVER – The Study of Women's Health Across the Nation has filled important knowledge gaps regarding bone loss rates at various stages of the menopausal transition, enabling physicians for the first time to make informed decisions about the appropriate time to screen for osteoporosis.
“Hypoestrogenic bone loss does not occur until the late transition. Duration of amenorrhea is the best predictor of when this process begins. There's no rationale to measure bone mineral density prior to 90 days of amenorrhea if postmenopausal osteoporosis is the clinical issue,” Dr. Nanette F. Santoro explained at the meeting.
“Bone mineral density at the lumbar spine and total hip starts dropping like a stone as soon as the women get to late menopause, so 3-11 months of amenorrhea is the tipping point for bone density. There is no point in assessing it sooner if you think they may have bone loss related to the menopause transition, because it's not going to be estrogen-related prior to this point,” said Dr. Santoro, a long-time SWAN (Study of Women's Health Across the Nation) investigator and chair of obstetrics and gynecology at the University of Colorado at Denver.
The SWAN findings have important clinical implications because most guidelines don't recommend routine screening of women for osteoporosis until age 65. That's too late. Since the rate of BMD loss accelerates markedly in late menopause, accompanied by an attendant increase in fracture risk, it makes sense to measure bone mineral density after a women has experienced 3 months of amenorrhea, and to intervene if she is beginning to lose bone rapidly, she continued.
SWAN showed that the annual rate of bone loss during the late perimenopausal and early postmenopausal years is 1.8%-2.3% in the lumbar spine and 1.0%-1.4% in the hip. At those rates, 5 years of bone loss would translate to a 7%-10% drop in BMD at the spine in the average woman, along with a 5%-7% decline at the hip. And that in turn foretells a 50%-100% higher fracture rate.
Another key SWAN finding regarding BMD changes during the menopausal transition is that rates of bone loss are markedly greater in women who are in the lowest tertile of body weight. Indeed, women in the top tertile for body weight had a 33%-55% slower rate of bone loss than did those in the lightest tertile. The apparent large ethnic differences in bone loss rates observed in SWAN turned out on closer inspection to be explained chiefly by ethnic differences in body weight.
SWAN is a long-term, longitudinal, observational study involving 3,302 women who were pre- or early perimenopausal at enrollment.
Participants were recruited from five ethnic groups – white, black, Hispanic, Japanese, and Chinese – at seven U.S. sites. The BMD substudy included 1,902 SWAN participants with BMD measurements obtained at up to six annual visits. The key findings of the BMD substudy have already been published (J. Clin. Endocrinol. Metab. 2008;93:861-8). Dr. Santoro, in her plenary lecture at the meeting, sought to spread the word.