1. What are osteoblast and osteoclast? What effect does phytoestrogen postulated to have on these cells?
Osteoclasts are a type of bone cell involved in the breakdown of worn out regions of bone, an activity that is stimulated by signals from osteocytes that determine which specific sites in the bone need replacement. Osteoblasts are another type of bone cell whose role is opposite that of osteoclasts – they bring about the synthesis or regeneration of bone tissues. Phytoestrogens such as isoflavone is postulated to enhance the formation of osteoblast cells while depressing the formation of osteoclasts (Poulsen and Kruger, 2008). Hence, the rate of bone synthesis is greater than the rate of bone breakdown.
2. What is the summary of findings of Table 1 and Figure 2 in the article #2 listed above? Just provide the summary of the findings.
Among 675 studies on the effects of isoflavone on bone, 10 randomized controlled trials which specifically measured spine bone mineral density (SBMD) or spine bone mineral content (SBMC) in relation to isoflavone intake were subjected to meta analysis. These studies have been conducted between 2000 to 2005 with participants ranging from 19 to 175 women, majority of whom were post-menauposal. Length of treatment was from 6 months to 2 years and dosage was from 4.4mg per day to 150mg per day of isoflavone in tablet form or in isolated soy protein form. Further evaluation of these studies revealed that only 6 strictly adhered to the procedure and methods of randomized controlled trials – the other four being deficient in areas such as definition of random, method of blinding or documentation of participant drop-outs (Ma, Qin, Wang and Katoh, 2008). Majority of the study results revealed that isoflavone supplementation led to an increase in BMD of the spine in postmenopausal women especially when taken as isolated soy protein form and with a dosage of 90mg per day for 6 months.
3. What is the summary of findings of Table 1 and Figure 2 in the article #3 listed above? Just provide the summary of findings.
Nine studies were selected on the basis that they were randomized controlled trials and measured bone-specific alkaline phosphatase (BAP) and deoxypiridinoline (Dpyr) as indicators of bone remodeling and bone breakdown respectively. Participants ranged from 4 to 48 women who were given either isoflavone in soy protein form, genistein or isoflavone tablets. Dosage ranged from 37.3mg per day to 118mg per day. The results of 8 studies pointed to an increase in BAP and a decrease in Dpyr in urine which means that bone remodeling occurred at a higher rate than bone resorption (Ma, Qin, Wang and Katoh, 2008). This effect was observed even if intake was less than 90mg per day and in shorter treatment duration.
4. Based on your readings, would you recommend isoflavone supplement for bone health? If so, to which population?
Regular isoflavone intake through dietary consumption of soy products or in tablet form has been correlated with higher bone mass density, hence healthier bones, in postmenopausal Asian women as suggested by the three studies. However, these effects have not been consistently documented among other populations of women who also obtained isoflavone supplementation. The varying results were attributed to the different types of isoflavones used, differences in dosage forms, differences in stage of menopause of the participants, differences in diet and metabolism, length of time of use, concurrent intake of calcium supplements and many other factors (Poulsen and Kruger, 2008). In addition, the researchers admitted that small sample sizes of their studies greatly limited the generalization of their conclusions. Therefore, until further studies provide conclusive evidence of the positive effects of isoflavone as comparable to current established therapies for osteoporosis such as calcium supplementation or hormone replacement therapy in postmenopausal women, isoflavone supplementation is not recommended except for Asian women who have long been obtaining the phytoestrogen through their diet.
List of References
Ma, D.F., Qin, L.Q., Wang, P.Y. and Katoh, R. (2008). “Soy isoflavone intake increases bone mineral density in the spine of menopausal women: meta analysis of randomized controlled trials”. Clinical Nutrition 27: 57-64.
Ma, D.F., Qin, L.Q., Wang, P.Y. and Katoh, R. (2008). “Soy isoflavone intake inhibits bone resorption and stimulates bone formation in menopausal women: meta analysis of randomized controlled trials”. European Journal of Clinical Nutrition 62:155-161.
Poulsen, R.C. and Kruger, M.C. (2008). “Soy phytoestrogens: impact on post-menopausal bone loss and mechanisms of action”. Nutrition Reviews 66(7): 359-374.