by Dr. Leo Galland
A research study just published in the American Journal of Clinical Nutrition found that women taking 120 milligrams per day of soy isoflavones as a dietary supplement lost less bone density at the hip over a three year period than did women receiving placebo. The researchers describe the effect as “modest”. The study was done by the Nutrition and Wellness Research Center at Iowa State University
In another recent study conducted by the Department of Foods and Nutrition at Purdue University, researchers found that genistein and related isoflavones may exert their effects on bone by decreasing resorption of existing bone, an effect similar to the effects of drugs like Actonel and Fosamax. Resorption is a natural process in which old bone is broken down so that new bone can be made. In the Purdue study, the antiresorptive effect of soy isoflavones was equal to 40% of the effect of Actonel.
Previous studies on the effects of soy isoflavones on bone loss have yielded mixed results. Research conducted in China and published in the European Journal of Nutrition found beneficial effects for soy isoflavones for the Chinese women in the study.
References and Abstracts:
Am J Clin Nutr. 2010 Jan;91(1):218-30. Epub 2009 Nov 11.The soy isoflavones for reducing bone loss (SIRBL) study: a 3-y randomized controlled trial in postmenopausal women. Alekel DL, Van Loan MD, Koehler KJ, Hanson LN, Stewart JW, Hanson KB, Kurzer MS, Peterson CT.Nutrition and Wellness Research Center, Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50010-8281, USA. email@example.com
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.
DESIGN: 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. Conclusion: Our results do not show a bone-sparing effect of extracted soy isoflavones, except for a modest effect at the femoral neck.
J Clin Endocrinol Metab. 2009 Oct;94(10):3798-805. Epub 2009 Jul 7.Antiresorptive effects of phytoestrogen supplements compared with estradiol or risedronate in postmenopausal women using (41)Ca methodology. Weaver CM, Martin BR, Jackson GS, McCabe GP, Nolan JR, McCabe LD, Barnes S, Reinwald S, Boris ME, Peacock M. Department of Foods and Nutrition, Purdue University, West Lafayette, Indiana 47907-2059, USA. firstname.lastname@example.org
INTRODUCTION: Reduction of ovarian estrogen secretion at menopause increases net bone resorption and leads to bone loss. Isoflavones have been reported to protect bone from estrogen deficiency, but their modest effects on bone resorption have been difficult to measure with traditional analytical methods.
METHODS: In this randomized-order, crossover, blinded trial in 11 healthy postmenopausal women, we compared four commercial sources of isoflavones from soy cotyledon, soy germ, kudzu, and red clover and a positive control of oral 1 mg estradiol combined with 2.5 mg medroxyprogesterone or 5 mg/d oral risedronate (Actonel) for their antiresorptive effects on bone using novel (41)Ca methodology.
RESULTS: Risedronate and estrogen plus progesterone decreased net bone resorption measured by urinary (41)Ca by 22 and 24%, respectively (P < 0.0001). Despite serum isoflavone profiles indicating bioavailability of the phytoestrogens, only soy isoflavones from the cotyledon and germ significantly decreased net bone resorption by 9% (P = 0.0002) and 5% (P = 0.03), respectively. Calcium absorption and biochemical markers of bone turnover were not influenced by interventions.
CONCLUSIONS: Dietary supplements containing genistein-like isoflavones demonstrated a significant but modest ability to suppress net bone resorption in postmenopausal women at the doses supplied in this study over a 50-d intervention period.
Eur J Nutr. 2006 Sep;45(6):327-34. Epub 2006 Jun 8.Soy isoflavones attenuate bone loss in early postmenopausal Chinese women : a single-blind randomized, placebo-controlled trial.Ye YB, Tang XY, Verbruggen MA, Su YX.Department of Nutrition, School of public Health Sun Yat-sen University, 74 Zhongshan Rd 2, Guangzhou, 510080, P.R. China. email@example.com
BACKGROUND: Previous studies show that daily doses of 40-99 mg soy isoflavones produce inconsistent effects on preventing estrogen-related bone loss in postmenopausal women. AIM OF THE STUDY: To examined the bone-sparing effect of isoflavones at a higher dose in early Chinese postmenopausal women.
METHODS: A total of 90 eligible women aged 45-60 years were randomly assigned to three treatment groups (30 subjects/group) with daily dosages of 0 (placebo), 84 and 126 mg isoflavones for 6 months. Further inclusion criteria included body mass index <30 kg/m(2) and Kuppermann Climacteric Scale >15. Bone mineral density (BMD) of the spine and hip were measured using dual- energy X-ray absorptiometry at 0 and 6 months. Serum osteocalcin, bone-specific alkaline phosphatase (BAP) and urinary deoxypyridinoline were examined at 0, 3 and 6 months.
RESULTS: Mean percent changes in BMD at the lumbar spine (p = 0.114) and femoral neck (p = 0.053) increased with the supplementations of soy isoflavones after adjusting for age, years since menopause, body weight and height, dietary intakes of isoflavones, calcium and protein, physical activities and baseline BMD at the relevant sites. We observed significantly dose-dependent linear relationship between the supplemental isoflavones and percent changes of BMD at the spine (p = 0.042) and femoral neck (p = 0.016) post-treatment, and urinary total deoxypyridinoline (p = 0.014) at 12 weeks but not at 24 weeks after adjusting for the above factors. No significant difference in percent changes in serum osteocalcin (p > 0.05) and BAP (p > 0.05) was found among the three treatment groups at 12-week and 24-week post-treatment.
CONCLUSION: There is a significantly dose-dependent effect of soy isoflavones on attenuating bone loss at the spine and femoral neck possibly via the inhibition of bone resorption in non-obese postmenopausal Chinese women with high Kuppermann Scale.