Prospective cohort study of soy food consumption and risk of bone fracture among postmenopausal women.

BACKGROUND Soy consumption has been shown to modulate bone turnover and increase bone mineral density in postmenopausal women. To our knowledge, no published studies have directly examined the association between soy consumption and risk of fracture. METHODS We examined the relationship between usual soy food consumption and fracture incidence in 24,403 postmenopausal women who had no history of fracture or cancer and were recruited between March 1, 1997, and May 23, 2000, in the Shanghai Women's Health Study, a cohort study of approximately 75,000 Chinese women aged 40 to 70 years. Usual soy food intake was assessed at baseline and reassessed during follow-up through in-person interviews using a validated food frequency questionnaire. Outcomes were ascertained by biennial in-person interview surveys. RESULTS During a mean follow-up of 4(1/2) years (110,243 person-years), 1770 incident fractures were identified. After adjustment for age, major risk factors of osteoporosis, socioeconomic status, and other dietary factors, the relative risks (95% confidence intervals) of fracture were 1.00, 0.72 (0.62-0.83), 0.69 (0.59-0.80), 0.64 (0.55-0.76), and 0.63 (0.53-0.76) across quintiles of soy protein intake (P<.001 for trend). The inverse association was more pronounced among women in early menopause. The multivariate relative risks (95% confidence intervals) of fracture comparing the extreme quintiles of soy protein intake were 0.52 (0.38-0.70) for women within 10 years of menopause vs 0.71 (0.56-0.89) for late postmenopausal women. Similar results were also found for intake of isoflavones. CONCLUSION Soy food consumption may reduce the risk of fracture in postmenopausal women, particularly among those in the early years following menopause.