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.