The association between soy isoflavone intake and menopausal symptoms after breast cancer diagnosis: a prospective longitudinal cohort study on Chinese breast cancer patients.

PURPOSE: This study investigated the association between soy isoflavone intake and menopausal symptoms (MPS) among Chinese women with early stage breast cancer in a prospective cohort study. METHODS: In an on-going prospective cohort study that involved 1462 Chinese women with early stage breast cancer, MPS were assessed at 18, 36 and 60 months after cancer diagnosis using the validated menopausal rating scale (MRS) questionnaire. Daily soy food intake for the previous 12 months was assessed at the same time using a validated food frequency questionnaire. The associations between MPS and soy isoflavone intake were evaluated in multivariable logistic regression analyses. RESULTS: The prevalence of MPS was almost the same during the first 60 months after cancer diagnosis, which were 64.5%, 65.2%, and 63.9% at 18, 36, and 60 months, respectively. Patients with MPS tended to be younger than those without MPS. The intake of soy isoflavones was not associated with the total score of MRS at 18-month follow-up [highest vs lowest tertile, odds ratio (OR) = 1.00, 95% CI 0.75-1.34]. Similarly, no significant association was noted at 36-month (OR = 1.25, 95% CI 0.92-1.69) and 60-month (OR = 1.21, 95% CI 0.84-1.74) follow-up. With regards to specific domain within MRS, the risk of symptoms presenting in somatic domain was higher among breast cancer patients who were in the highest tertile of soy isoflavone intake at 36 months post-diagnosis (OR = 1.44, 95% CI 1.07-1.94, P-trend = 0.02), compared with the lowest tertile, where a stronger significant association was noted among patients who were younger than 60 years (OR = 1.52, 95% CI 1.05-2.20, P-trend = 0.03) and pre-menopausal (OR = 3.81, 95% CI 1.85-8.11, P-trend < 0.01). CONCLUSION: The present study provided further evidence that soy isoflavone consumption was not associated with MPS among Chinese breast cancer patients. In fact, patients with higher intake of soy isoflavone have increased risk of experiencing somatic symptoms.