Isoflavone combined with exercise on bone mineral density in postmenopausal women: A systematic review and meta-analysis of randomized controlled trials

Effects of Isoflavone Interventions on Bone Metabolism in Perimenopausal and Postmenopausal Women: An Umbrella Review of Meta-Analyses of Randomized Controlled Trials

OBJECTIVE

Previous meta-analyses have investigated the effects of isoflavones on bone metabolism in perimenopausal or postmenopausal women. However, there were still conflicting results. Thereby, this umbrella review assessed the existing meta-analysis evidence of the effects of isoflavone interventions on bone metabolism in perimenopausal and postmenopausal women.

METHODS

This study was conducted following the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. From the inception until August 24, 2023, PubMed, Embase, Cochrane, and Web of Science databases were searched to identify meta-analyses of randomized controlled trials. The outcomes included bone mineral densities (BMDs), and bone turnover markers of osteocalcin, bone-specific alkaline phosphatase, pyridinoline, deoxypyridinoline, Procollagen Type 1 N-Terminal Propeptide, and C-telopeptide of Type 1 Collagen. The random-effects model was used to recalculate the extracted effect sizes. Mean difference (MD) was used as a summary effect measure.

RESULTS

Ten meta-analyses of randomized controlled trials were included. The isoflavone intervention was associated with increased BMDs in lumbar spine (MD: 11.50 mg/cm2, 95% confidence interval (CI): 6.46 to 16.55), femoral neck (MD: 2.03%, 95% CI: 0.57 to 3.50), and top hip (MD: 0.31%, 95% CI: 0.03 to 0.59) in perimenopausal and postmenopausal women.

CONCLUSION

Our findings indicate that isoflavone interventions have the potential to improve BMD at different bone sites, including the lumbar spine, femoral neck, and total hip in perimenopausal and postmenopausal women. Isoflavone may be considered a complementary option in the bone loss of perimenopausal and postmenopausal women.

Isoflavone intervention and its impact on bone mineral density in postmenopausal women: a systematic review and meta-analysis of randomized controlled trials

Due to estrogen deficiency, postmenopausal women may suffer from an imbalance in bone metabolism that leads to bone fractures. Isoflavones, a type of phytoestrogen, have been suggested to improve bone metabolism and increase bone mass. Therefore, isoflavones are increasingly recognized as a promising natural alternative to hormone replacement therapy for postmenopausal women who face a heightened risk of osteoporosis and are susceptible to bone fractures.

PURPOSE

This study aimed to evaluate the efficacy of isoflavone interventions on bone mineral density (BMD) in postmenopausal women by means of systematic review and meta-analysis.

METHODS

The electronic database searches were performed on PubMed, Embase, Scopus, and Cochrane Library databases, covering literature up to April 20, 2023. A random-effects model was used to obtain the main effect estimates, with a mean difference (MD) and its 95% confidence interval (CI) as the effect size summary. The risk of bias assessment was conducted using the Risk of Bias 2 (RoB2) tool.

RESULTS

A total of 63 randomized controlled trials comparing isoflavone interventions (n = 4,754) and placebo (n = 4,272) were included. The results indicated that isoflavone interventions significantly improved BMD at the lumbar spine (MD = 0.0175 g/cm2; 95% CI, 0.0088 to 0.0263, P < 0.0001), femoral neck (MD = 0.0172 g/cm2; 95% CI, 0.0046 to 0.0298, P = 0.0073), and distal radius (MD = 0.0138 g/cm2; 95% CI, 0.0077 to 0.0198, P < 0.0001) in postmenopausal women. Subgroup analysis showed that the isoflavone intervention was effective for improving BMD when the duration was ≥ 12 months and when the intervention contained genistein of at least 50 mg/day.

CONCLUSION

This systematic review and meta-analysis suggests that isoflavone interventions, especially those containing genistein of at least 50 mg/day, can effectively enhance BMD in postmenopausal women.

Current Perspectives on the Beneficial Effects of Soybean Isoflavones and Their Metabolites for Humans

Soybeans are rich in proteins and lipids and have become a staple part of the human diet. Besides their nutritional excellence, they have also been shown to contain various functional components, including isoflavones, and have consequently received increasing attention as a functional food item. Isoflavones are structurally similar to 17-β-estradiol and bind to estrogen receptors (ERα and ERβ). The estrogenic activity of isoflavones ranges from a hundredth to a thousandth of that of estrogen itself. Isoflavones play a role in regulating the effects of estrogen in the human body, depending on the situation. Thus, when estrogen is insufficient, isoflavones perform the functions of estrogen, and when estrogen is excessive, isoflavones block the estrogen receptors to which estrogen binds, thus acting as an estrogen antagonist. In particular, estrogen antagonistic activity is important in the breast, endometrium, and prostate, and such antagonistic activity suppresses cancer occurrence. Genistein, an isoflavone, has cancer-suppressing effects on estrogen receptor-positive (ER+) cancers, including breast cancer. It suppresses the function of enzymes such as tyrosine protein kinase, mitogen-activated kinase, and DNA polymerase II, thus inhibiting cell proliferation and inducing apoptosis. Genistein is the most biologically active and potent isoflavone candidate for cancer prevention. Furthermore, among the various physiological functions of isoflavones, they are best known for their antioxidant activities. S-Equol, a metabolite of genistein and daidzein, has strong antioxidative effects; however, the ability to metabolize daidzein into S-equol varies based on racial and individual differences. The antioxidant activity of isoflavones may be effective in preventing dementia by inhibiting the phosphorylation of Alzheimer's-related tau proteins. Genistein also reduces allergic responses by limiting the expression of mast cell IgE receptors, which are involved in allergic responses. In addition, they have been known to prevent and treat various diseases, including cardiovascular diseases, metabolic syndromes, osteoporosis, diabetes, brain-related diseases, high blood pressure, hyperlipidemia, obesity, and inflammation. Further, it also has positive effects on menstrual irregularity in non-menopausal women and relieving menopausal symptoms in middle-aged women. Recently, soybean consumption has shown steep increasing trend in Western countries where the intake was previously only 1/20-1/50 of that in Asian countries. In this review, I have dealt with the latest research trends that have shown substantial interest in the biological efficacy of isoflavones in humans and plants, and their related mechanisms.