Prebiotics and synbiotics containing fructooligosaccharides enhance mineral bioavailability by improving the absorption of minerals in the colon, especially calcium, iron, and magnesium (Caers, 2004; Coudray, 2004; Hidaka et al., 2001; Ohta et al., 1994; Roberfroid, 2005). The mechanism for this is probably enhanced passive and active mineral transport across the intestinal epithelium, mediated by increased levels of butyrate and other short-chain fatty acids and decreased pH (ScholzAhrens and Schrezenmeir, 2002). Improvements in calcium and iron absorption may help prevent osteoporosis and anemia, respectively (Ohta et al., 1998; Weaver and Liebman, 2002). Fructooli-gosaccharide ingestion enabled rats, for instance, to recover from experimentally induced anemia and to increase levels of minerals in their bones (Ohta et al., 1998; Oda et al., 1994).
Osteoporosis is a condition characterized by a decrease in bone mass and density that causes the bones, especially in postmenopausal women, to become fragile and vulnerable to fracture. It is a growing global problem, which can be alleviated by dietary approaches. Calcium is a key factor in bone strength. By optimizing peak bone mass in early adulthood and by minimizing bone loss during the postmenopausal period, the risk, for example, of hip fracture can be significantly reduced. Improved calcium nutrition during development is critical and can reduce hip fracture rates later in life by around 50% (Coxam, 2005).
Prebiotic inulin and fructooligosaccharides added to the daily diet of animals significantly increase calcium absorption in animals (e.g., Coudray et al., 2003; Mineo et al., 2001; Ohta et al., 1994; Remesy et al., 1993). This can increase mineralization and bone mineral density (Roberfroid et al., 2002b). In humans, a beneficial effect on calcium absorption is found in both adolescents (Griffin et al., 2002, 2003; van den Heuvel et al., 1999) and postmenopausal women (van den Heuvel et al., 2000). In both groups, a mixture of inulins having low and high degrees of polymerization (DP) were the most effective treatment for enhancing mineral absorption (Coudray et al., 2003; Griffin et al., 2002, 2003). Such a mixture (e.g., a 1:1 ratio of fructooligosaccharides (average DP of 4) and long-chain inulin (average of DP 25)) increased the calcium accretion to the skeleton by ~30 mg Caday-1 (Abrams et al., 2005). Polymorphisms in the vitamin D receptor gene (Fok1), however, appear to strongly modulate calcium absorption and the magnitude of the response to supplementation.
In Japan, where mineral deficiency can be a nutritional problem, the beneficial effects of fructooligosaccharides on calcium absorption have been recognized in the labeling on dietary supplements since 1999 (Hidaka et al., 2001).
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