Relationship between urinary phytoestrogen levels and Z score of lumbar vertebral bone mineral density in Japanese postmenopausal women

Phytoestrogens are attracting much attention for their anticancer effects, their reduction of menopausal symptoms, and their preventive effects against osteoporosis in the human body, resulting from the consumption of foods that contain phytoestrogens at high concentrations. The effects of 2 phytoestrogens, genistein and daidzein, have been reported, but little data have been published on the effects of equol, coumesterol, and other phytoestrogens. In the present study, using high-performance liquid chromatogaphy, we measured the urinary phytoestrogen levels of 80 postmenopausal Japanese women and simultaneously determined the bone mineral density (BMD) in lumbar vertebrae L2 through L4 (L2-L4BMD), measured the levels of the bone biochemical markers and calciotropic hormones, and also studied the relationships of these with urinary phytoestrogens. Our results showed the following values for phytoestrogens in grams per milligram of creatinine: daidzein, 3.11 ± 3.09; genistein, 2.74 ± 5.02; equol, 6.29 ± 11.44; coumesterol, 0.51 ± 0.77; O-desmethylangolensin (DMA), 1.59 ± 5.19; formononetin, 0.11 ± 0.19; and biochanin A, 0.08 ± 0.19. When these were converted to logarithms, log (genistein) was the only one to show a statistically significant positive correlation (r = 0.29, P < .05) with the Z score of L2-4BMD. Log (DMA) showed a negative correlation (r = −0.36, P < .013) with the urinary deoxypyridinoline level. The levels of osteocalcin and the calciotropic hormones showed no correlation with urinary phytoestrogen levels. The fact that there were correlations between the genistein level and Z score of bone density, and between DMA and biochemical markers of bone metabolism, suggested that phytoestrogens may have an effect on bone metabolism in Japanese women. Genistein and DMA might be involved in the inhibition of bone resorption in terms of the correlation between phytoestrogens levels and BMD.