Effect of a mixture of calcium, vitamin D, inulin and soy isoflavones on bone metabolism in post-menopausal women: a retrospective analysis

Objectives Aging might affect the effectiveness of the sole supplementation of calcium and vitamin D in postmenopausal women, due to the development of vitamin D resistance in the gut, which limits calcium absorption. Thus, we wanted to test the efficacy of a mixture of calcium (500 mg), 25-hydroxyvitamin D [ 25(OH) D; 300 IU], inulin (3 g) and soy isoflavones (40 mg), to improve calcium absorption in this type of population. Study design It is a retrospective study on otherwise healthy post-menopausal women. Main outcome measures The following parameters were evaluated at baseline and after 3 months of supplementation: daily calciuria as an indirect marker of calcium absorption, serum 25(OH) D, parathormone, insulin-like growth factor 1 (IGF1) as a marker of bone anabolism, collagen telopeptide and osteocalcin as markers of bone resorption and bone turnover, respectively. Results Twenty-eight women (median age 67 years) were included in the analysis. The supplementation markedly increased daily calciuria (+60 %; p = 0.00009), while reducing parathormone levels (-18 %; p = 0.02) and leaving 25(OH) D unaltered. An increase in IGF1 (+16 %; p = 0.01) and a reduction in collagen telopeptide (-17 %; p = 0.04) were observed, too, as well as a modest trend towards osteocalcin reduction, although not significant. Conclusions These results suggest that the considered mixture improved intestinal calcium absorption and bone metabolism in post-menopausal women. Since the amount of supplemented calcium was relatively low and 25(OH) D levels were unchanged, the observed effects are likely due to the combined contributions of inulin and soy isoflavones.