Isoflavone Research Initiative

The most recent findings on soy and isoflavones were presented in Washington DC on the occasion of the 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment (October 16-19, 2010). A major part of the topics was dedicated to safety and health benefits in menopausal women, and to the issue of soy and breast cancer.

Dr. Lee Alekel (Iowa State University, Ames, USA) performed a randomized placebo-controlled double-blind trial aimed on the detection of bone-strength-preserving effects of 80 and 120 mg soy isoflavones supplemented by postmenopausal women (Shedd-Wise et al. 2010). The bone-protective effects of isoflavones are still under debate: Among others, Alekel had published positive effects, whereas in a more recent study Brink had not found an effect (Alekel et al. 2000; Brink et al. 2008). Short-term studies suggested that isoflavones may have a bone-sparing effect, but Alekel et al. were unable to confirm such as effect in a three-year trial (Alekel et al. 2010). The measurement of bone mineral density is possibly not an ideal parameter for the assessment of protective isoflavone effects. Bone strength would appear to be a much more relevant factor when it comes to the prevention of bone fractures – however, none of the studies on isoflavones performed to date has examined bone strength.

The working group measured three-year changes in parameters of bone mineral density and bone strength at predefined localisations of the femoral bone in women supplemented with 500 mg calcium and 600 IU vitamin D3. The women were distributed to either placebo (n = 78), 80 mg (n = 78) or 120 mg (n = 78) of isoflavones (Novasoy; 50 % genistein, 40 % daidzein and 10 % glycytein). None of the subjects was diagnosed with osteoporosis, and none was treated with hormones.

Over the 36 months of observation bone mineral density decreased in all groups, with no significant difference between groups. The supplementation of isoflavones had no protective effect on bone mineral density. In contrast, the isoflavones showed bone-strength-preserving effects (as measured by computer tomography), and markers of bone formation/resorption such as CTx and urinary phosphate were significantly improved. Significant effects were likewise found with BALP. Soy isoflavone treatment for three years was found modestly beneficial for bone health, and most interestingly the effect was best in women with a higher bone turnover.

References

Alekel DL, Germain AS, Peterson CT, Hanson KB, Stewart JW and Toda T (2000). Isoflavone-rich soy protein isolate attenuates bone loss in the lumbar spine of perimenopausal women. Am J Clin Nutr 72(3):844-852.

Alekel DL, Van Loan MD, Koehler KJ, Hanson LN, Stewart JW, Hanson KB, Kurzer MS and Peterson CT (2010). The soy isoflavones for reducing bone loss (SIRBL) study: a 3-y randomized controlled trial in postmenopausal women. Am J Clin Nutr 91(1):218-230.

Brink E, Coxam V, Robins S, Wahala K, Cassidy A and Branca F (2008). Long-term consumption of isoflavone-enriched foods does not affect bone mineral density, bone metabolism, or hormonal status in early postmenopausal women: a randomized, double-blind, placebo controlled study. Am J Clin Nutr 87(3):761-770.

Shedd-Wise KM, Alekel DL, Hofmann H, Hanson KB, Schiferl DJ, Hanson LN and Van Loan MD (2010). Soy isoflavones for reducing bone loss (SIRBL) stuty: Three year effects on pQCT bone density and strength in postmenopausal women. 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment, Washington DC, 16-19 October.