Lu LJW, et al. - The researchers conducted double-blind, randomized, placebo-controlled study to investigate the novel effects of phytoestrogenic soy isoflavones on serum calcium and chloride in premenopausal women. They observed mean changes for calcium and for chloride, with each visit among the study population. These novel and strong effects of soy isoflavones on calcium homeostasis had important implications for long-term effects of these natural substances on cardiovascular diseases.

Methods

• The researchers randomly assigned 197 premenopausal women to either isoflavone (N=99) or placebo pills (N=98) 5 days per week for up to 2 years, plus prenatal vitamins.
• Isoflavone pills contained 60 mg genistein, 60 mg daidzein and 16.6 mg glycitein (expressed as aglycone equivalents).
• In this study, all pills contained 15 mg riboflavin as an adherence marker.
• They measured blood chemistries and urinary daidzein, genistein and riboflavin multiple times during the luteal phase before and during treatment.

Results

• Analysis of the adherent population (N=83 per group), showed significantly strong relationships between urinary levels of isoflavones and serum concentrations of calcium (regression coefficients 0.082 for daidzein and 0.229 for genistein, all P < 0.01) and chloride (regression coefficient, -1.537 for genistein, P < 0.0001), mediated in part by albumin.
• With each visit for subjects excreting the most vs. the least amounts of isoflavones, the effects amounted to mean changes of +0.24 mg/dL for calcium and -1.45 mEq/L for chloride.
• No evidence was found for these associations in the intention-to-treat analysis (N=197) that did not evaluate expected variations in isoflavone levels within and between subjects from metabolism and adherence.