June 20, 2007 — Treatment with 54 mg/day of the soy isoflavone genistein for 2 years is effective in preventing bone loss caused by estrogen deficiency, according to the results of a randomized, double-blind, placebo-controlled trial of postmenopausal women published in the June 19 issue of the Annals of Internal Medicine.
"Observational studies and small trials of short duration suggest that the isoflavone phytoestrogen genistein reduces bone loss, but the evidence is not definitive," write Herbert Marini, MD, from the University of Messina in Italy, and colleagues. "As a natural selective estrogen receptor modulator, genistein may positively regulate bone cell metabolism without harmful estrogenic activity in the breast and uterus."
At 3 university medical centers in Italy, 389 postmenopausal women with osteopenia (bone mineral density [BMD], < 0.795 g/cm2 at the femoral neck) and no significant comorbid conditions were randomized to receive 54 mg/day of genistein or placebo control daily for 24 months. Study medications in both groups included calcium and vitamin D. All women underwent a 4-week stabilization period during which they received a low-soy, reduced-fat diet.
The main endpoint was BMD at the anteroposterior lumbar spine and femoral neck at 24 months. Secondary outcomes were serum levels of bone-specific alkaline phosphatase and insulin-like growth factor I, urinary excretion of pyridinoline and deoxypyridinoline, and endometrial thickness.
After 2 years, women who took genistein had greater BMD and improved markers of bone metabolism than did women who took only calcium and vitamin D (P < .001). The BMD actually increased at both sites in those who took genistein, whereas it decreased at both sites in the control group.
Compared with the control, genistein was associated with statistically significant decreases in urinary excretion of pyridinoline and deoxypyridinoline and increased bone-specific alkaline phosphatase and insulin-like growth factor I.
Women in the genistein group did not have increased endometrial thickness, which is an adverse event associated with some hormonal treatments of low bone density. The genistein group had more gastrointestinal adverse effects than did the control group (19% vs 8%; P = .002), and more in this group discontinued participating in the study.
Study limitations include lack of data on fractures and limited power to evaluate adverse effects.
"Two years of treatment with genistein improved BMD and markers of bone turnover in a cohort of osteopenic postmenopausal women," the authors write. "On the basis of these data, future studies in osteoporotic women are warranted to determine whether genistein also significantly decreases fracture risk in this group. In addition, studies are warranted to determine whether genistein positively affects bone loss not related to postmenopausal ovarian hormone loss, such as glucocorticoid-induced osteoporosis."
The Italian Ministry of Education, University and Research and the University of Messina supported this study. The authors have disclosed no relevant financial relationships.
Ann Intern Med. 2007;146:839-847.
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