Use of dietary supplements containing soy isoflavones and breast cancer risk among women aged >50 y: a prospective study

Am J Clin Nutr. 2019 Mar 1;109(3):597-605. doi: 10.1093/ajcn/nqy313.

Abstract

Background: Soy-based dietary supplements have been promoted as natural alternatives to menopausal hormone therapy, but their potential effect on breast cancer development is controversial.

Objectives: We examined the relation between the consumption of soy supplements and the risk of breast cancer, overall and by tumor hormone receptor status, among women aged >50 y.

Methods: In total, 76,442 women from the Etude Epidemiologique aupres de Femmes de la Mutuelle Generale de l'Education Nationale (E3N) cohort, born between 1925 and 1950, were followed from 2000 to 2011 (11.2 y on average, starting at a mean age of 59.5 y; 3608 incident breast cancers), with soy supplement use assessed every 2-3 y. HRs of breast cancer were estimated with the use of multivariable Cox models.

Results: Compared with never using soy supplements, the HRs associated with current use of soy supplements were 0.92 (95% CI: 0.76, 1.11) for all, 0.78 (95% CI: 0.60, 0.99) for estrogen receptor (ER)-positive, and 2.01 (95% CI: 1.41, 2.86) for ER-negative breast cancers. There was no association between past use of soy supplements and breast cancer. HRs for current use were 1.36 (95% CI: 0.95, 1.93) and 0.82 (95% CI: 0.65, 1.02) among women with and without a family history of breast cancer, respectively (P-interaction = 0.03) and 1.06 (95% CI: 0.87, 1.30) ≥5 y after menopause compared with 0.50 (95% CI: 0.31, 0.81) in premenopause or ≤5 y postmenopause (P-interaction = 0.04).

Conclusions: In this cohort of women aged >50 y, we report opposing associations of soy supplements with ER-positive and ER-negative breast cancer risk. Our results also caution against the use of these supplements in women with a family history of breast cancer. Whether the risk profile of soy supplements could be more favorable among premenopausal or recently postmenopausal women deserves further investigation.

Keywords: breast cancer; cohort; dietary supplements; hormone receptors; isoflavones; prospective study; soy; women aged over 50 years.

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Breast Neoplasms / epidemiology
  • Breast Neoplasms / etiology*
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Cohort Studies
  • Dietary Supplements / analysis*
  • Female
  • Follow-Up Studies
  • Humans
  • Isoflavones / administration & dosage*
  • Isoflavones / adverse effects
  • Menopause / drug effects*
  • Menopause / genetics
  • Menopause / metabolism
  • Middle Aged
  • Prospective Studies
  • Receptors, Estrogen / genetics
  • Receptors, Estrogen / metabolism
  • Risk Factors

Substances

  • Carrier Proteins
  • Isoflavones
  • Receptors, Estrogen
  • estrophilin