One-year soy isoflavone supplementation prevents early postmenopausal bone loss but without a dose-dependent effect

It is believed that soy isoflavone has much potential effectiveness on the postmenopausal status; however, the optimal dose for preventing postmenopausal bone loss still remains unclear. This open-labeled, self-controlled pilot study was undertaken to determine the effect of 1-year supplementation of different high dosages of soy isoflavone in postmenopausal Taiwanese women. Forty-three women aged 45–67 years were enrolled and randomly assigned into a control (C), 100 mg/day isoflavone (IF100) and 200 mg/day isoflavone (IF200) groups for 1 year. Dual-energy X-ray absorptiometry and other related biochemical markers of bone metabolism were measured. Results indicated that the decrease in bone mineral density (BMD) was significant for lumbar vertebrae L1–3, L1–4 and the femur neck in the C group; surprisingly, the BMD of L1–3 was significantly elevated in the IF100 group; however, there were no consistent responses in the IF200 group. No significant change except loss of the bone mineral content of Ward's triangle (P=.003) was found in the IF200 group after treatment. The percentage change at L1–3 was less (P=.04) in the IF200 group when compared to the IF100 group. A relatively uniform direction of bone formation in expanding the weight and area with different rates of change resulted in different BMD changes. Both indicated a change of bone formation patterns with the higher-dose supplement. A protective effect of IF100 on estrogen-related bone loss was observed. A lack of a benefit such as high safety in the IF200 group for 1-year administration was ensured and lacked undesirable side effects.