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In Premenopausal Breast Cancer, Soy Reduces Fracture Risk

Boiled soybeans.

According to a new study, consuming soy-containing foods and maintaining a healthy weight can help pre- and perimenopausal survivors of breast cancer to reduce their risk of fractures.

Survivors of breast cancer are at a significantly increased risk of osteoporosis-related fractures, largely due to a reduction in bone mineral density caused by estrogen deprivation therapies. In addition, chemotherapy or ablation of ovarian function can induce premature menopause among younger patients with breast cancer, decreasing bone mineral density. For the study, published in JNCI Cancer Spectrum, researchers sought to investigate whether the increased risk of fracture could be influenced by several lifestyle-related factors: body mass index, exercise, and soy consumption.

Body mass index and exercise are both associated not only with physical fitness but also with estrogen levels; they have previously been studied for associations with bone mineral density and fracture risk in postmenopausal women. Soy contains high levels of isoflavones, selective estrogen receptor modulators associated with reducing risk of death and recurrence in patients with breast cancer. In addition, consumption of soy has been linked to lowered risk of fracture in healthy postmenopausal women, especially during early menopause. Prior to the current study, however, these factors—body mass index, exercise, and soy consumption—had not been adequately researched in survivors of breast cancer, particularly younger survivors.

The investigators analyzed data on 4,139 stage 0 to III patients with breast cancer, including 1,987 pre- and perimenopausal patients and 2,152 postmenopausal patients, from the Shanghai Breast Cancer Survival Study. They assessed fractures at 18 months and at three, five, and 10 years after cancer diagnosis. Weight and height were assessed at baseline, and exercise and soy isoflavone intake were assessed at six months and at 18 months following diagnosis.

The researchers found a 10-year osteoporotic fracture incidence of 2.9% for pre- and perimenopausal patients and an incidence of 4.4% for postmenopausal patients. High consumption of soy isoflavones was correlated with reduced fracture risk in pre- and perimenopausal patients but not in postmenopausal patients; in addition, being overweight increased risk in pre- and perimenopausal patients but not in postmenopausal patients. In postmenopausal patients, exercise was associated with reduced fracture risk in a dose-response pattern. Use of tamoxifen was also associated with a reduced risk of fractures, both of any fractures and of osteoporotic fractures.

"The menopausal transition is known to be a period of high risk for bone loss, and given the relative scarcity of data related to fracture risk among younger women with breast cancer, this study marks an important contribution to this body of literature," commented one of the study's co-lead authors, Evelyn Hsieh, MD, PhD, Assistant Professor of Medicine and of Epidemiology at Yale School of Medicine. "Our findings, in particular regarding the protective effects of soy food consumption, provide novel insight into how future interventions can be best tailored to different risk groups."

For More Information

Zheng N, Hsieh E, Cai H, et al (2019). Soy food consumption, exercise, and body mass index and osteoporotic fracture risk among breast cancer survivors: the Shanghai Breast Cancer Survival Study. JNCI Cancer Spectr, 3(2):pkz017. DOI:10.1093/jncics/pkz017

Image credit: Masaaki Komori. Licensed under CC BY-SA 2.0

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