Fewer fractures: Soy consumption linked to reduced risk of osteoporotic bone breaks in breast cancer patients

21 May 2019 --- Researchers have investigated the impact that Body Mass Index (BMI), exercise and consumption of soy food have on bone fracture rates among breast cancer survivors. A decade-long study found that higher soy intake was associated with a 77 percent reduced risk of osteoporotic fractures in younger women while exercise showed a significantly reduced risk of fractures among older women. One of the key findings is that the novel association of soy food intake with osteoporotic fractures in breast cancer survivors could help guide future treatments, but authors indicate that further research needs to be carried out.

The research also notes that the extended use of breast cancer drug tamoxifen showed a 37 percent reduced risk of fractures in the overall study population. Tamoxifen is a selective estrogen receptor modulator (SERM) that causes an increase in bone mineral density. Soy-based foods, which are rich in isoflavones, provide a natural SERM.

Breast cancer is the second most common cancer among women in the US, with one in eight women diagnosed with the disease during their lifetime. Many treatments for breast cancer can cause premature menopause and decrease bone mineral density, which leads to a higher rate of bone fractures.

A new paper entitled “Soy Food Consumption, Exercise and Body-Mass-Index and Osteoporotic Fracture Risk among Breast Cancer Survivors” is in JNCI Cancer Spectrum, published by Oxford University Press. It is the first study to find that diets high in soy foods are associated with a decreased risk of osteoporotic bone fractures in premenopausal breast cancer survivors.

The study used data from the Shanghai Breast Cancer Survival Study of 5,042 newly diagnosed breast cancer survivors between the ages of 20 and 75. Researchers collected detailed information including cancer diagnosis and treatment history, medication use, dietary habits, exercise and other lifestyle factors. 

Just over half (52 percent) of women in the study were postmenopausal. Patients then had follow-up visits at 18 months, and three, five and 10 years after their diagnosis to update exposure and outcome information.

Over the next 10 years, 3.6 percent of survivors reported an osteoporotic bone fracture.

This prospective study included 4,139 stage 0–III breast cancer patients and 1987 pre-/perimenopausal as well as 2152 postmenopausal patients. Osteoporotic fractures were defined as fractures caused by falls from standing height and at sites associated with osteoporosis. Exercise and soy isoflavone intake were assessed at six and 18 months post-diagnosis. Weight and height were measured at baseline. Life table and Cox regression analyses were also employed, while all statistical tests were two-sided.

The abstract of the study also explains how breast cancer patients have a higher incidence of osteoporosis-related fractures compared with age-matched healthy women. This increased risk is largely attributed to the decrease in bone mineral density (BMD) that occurs as a result of therapies that induce estrogen deprivation, a well-established risk factor for osteoporosis and associated bone fracture. 

Such treatments, the paper highlights, include endocrine therapies, such as tamoxifen or aromatase inhibitors, which are common adjuvant treatments for hormone receptor-positive breast cancers, the most common type of breast cancer. In addition, chemotherapy or ablation of ovarian function (either medically or surgically) can lead to premature menopause among younger women and reduce BMD. 

This is not the first time the qualities of soy have been touted in relation to bone health. Last August, researchers from the University of Missouri discovered, through an animal study, that soy protein found in food might counter the negative effects of menopause on bone and metabolic health. Moreover, the researchers believe that soy protein might also have positive impacts on bone strength for women who have not yet reached menopause.

This latest study concluded that “the novel association of soy food intake with osteoporotic fractures in breast cancer survivors if confirmed, can help guide future strategies for fracture risk reduction in this vulnerable population.”