The soy isoflavones for reducing bone loss (SIRBL) study: a 3-y randomized controlled trial in postmenopausal women.
BACKGROUND
Our previous study indicated that soy protein with isoflavones lessened lumbar spine bone loss in midlife women.


OBJECTIVE
We examined the efficacy of isoflavones (extracted from soy protein) on bone mineral density (BMD) in nonosteoporotic postmenopausal women. We hypothesized that isoflavone tablets would spare BMD, with biological (age, body weight, serum 25-hydroxyvitamin D) and lifestyle (physical activity, dietary intake) factors modulating BMD loss.


METHODS
Our double-blind, randomized controlled trial (36 mo) included healthy postmenopausal women (aged 45.8-65.0 y) with intent-to-treat (n = 224) and compliant (n = 208) analyses. Treatment groups consisted of a placebo control group and 2 soy isoflavone groups (80 compared with 120 mg/d); women received 500 mg calcium and 600 IU vitamin D(3). Outcomes included lumbar spine, total proximal femur, femoral neck, and whole-body BMD.


RESULTS
Analysis of variance for intent-to-treat and compliant (> or =80%) models, respectively, showed no treatment effect for spine (P = 0.46, P = 0.21), femur (P = 0.86, P = 0.46), neck (P = 0.17, P = 0.14), or whole-body (P = 0.86, P = 0.78) BMD. From baseline to 36 mo, BMD declined regardless of treatment. In intent-to-treat and compliant models, respectively, BMD decreases were as follows: spine (-2.08%, -1.99%), femur (-1.43%, -1.38%), neck (-2.56%, -2.51%), and whole body (-1.66%, -1.62%). Regression analysis (compliant model) indicated that age, whole-body fat mass, and bone resorption were common predictors of BMD change. After adjustment for these factors, 120 mg (compared with placebo) was protective (P = 0.024) for neck BMD. We observed no treatment effect on adverse events, endometrial thickness, or bone markers.


CONCLUSIONS
Our results do not show a bone-sparing effect of extracted soy isoflavones, except for a modest effect at the femoral neck. This trial was registered at clinicaltrials.gov as NCT00043745.
Alekel
D Lee
DL
Nutrition and Wellness Research Center, Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50010-8281, USA. alekel@iastate.edu
Van Loan
Marta D
MD
Koehler
Kenneth J
KJ
Hanson
Laura N
LN
Stewart
Jeanne W
JW
Hanson
Kathy B
KB
Kurzer
Mindy S
MS
Peterson
C Theodore
CT
D000368:Aged; D015519:Bone Density / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000627:therapeutic use; D002140:California; D002762:Cholecalciferol / Q000627:therapeutic use; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007484:Iowa; D007529:Isoflavones / Q000008:administration & dosage / Q000627:therapeutic use*; D008019:Life Style; D008875:Middle Aged; D010024:Osteoporosis / Q000517:prevention & control*; D018579:Patient Selection; D017698:Postmenopause / Q000187:drug effects / Q000502:physiology*; D013025:Glycine max; D011795:Surveys and Questionnaires; D013607:Tablets
D007529:Isoflavones; D013607:Tablets; D002762:Cholecalciferol; D002118:Calcium