Calcium from Finger Millet—A Systematic Review and Meta-Analysis on Calcium Retention, Bone Resorption, and In Vitro Bioavailability

Calcium deficiency during child growth leads to osteoporosis in later stages of life. Finger millet is one of the calcium dense foods, with three times the level of calcium than milk, and the only cereal that contains high calcium content which is consistent across different varieties (364 ± 58 mg/100 g). Thus, finger millet has potential for addressing calcium deficiency naturally. This study aimed to determine the retention and impact of finger millet calcium on bone turnover through a systematic review and meta-analysis. Three human studies were eligible for systematic review. Of these, only two were eligible for meta-analysis to assess the retention of calcium in children of 9 to 12 years. One study on bone turnover markers was not used in the meta-analysis as at least two studies are required to conduct meta-analysis. Due to the lack of complete data only four studies were eligible for meta-analysis to assess the in vitro bioavailability of calcium from unprocessed and a range of different types of processed finger millet. The result shows that there was significant retention (p < 0.05) of 23.4 ± 2.9% calcium from finger-millet-based diet which could help bone accretion during child growth if finger-millet-based diet is consumed. The bone turnover marker study shows that the resorption of calcium reduced by 28% and 47% among peri and post-menopausal women respectively after feeding the nutria mixed grain ball. However, there is no significant change in bone formation marker. Depending on the type of processing, calcium bioavailability either increased or decreased. One in vitro study showed that calcium bioavailability from finger millet was 28.6% when boiled, whereas three studies on processing show that certain processing can double the calcium bioavailability to 61.4%. Irrespective of the type of processing, finger millets contribute to high calcium retention and extremely high bioavailable calcium and could be useful for healthy growth and in dealing with complications related to calcium deficiency.

Calcium Bioavailability in the Soluble and Insoluble Fibers Extracted from Opuntia ficus indica at Different Maturity Stages in Growing Rats

Childhood and adolescence are crucial stages of life for bone health. Therefore, an adequate calcium intake and a healthy life style constitute the main strategies to prevent the risk of osteoporosis-related fractures during adulthood. It has been demonstrated that inclusion of indigestible carbohydrates in foods can help improve calcium absorption in growing stages. The objective of this study was to evaluate the effect of supplementation of soluble and insoluble fibers extracted from O. ficus indica cladodes on calcium bioavailability. Male Wistar rats 4-week old were fed diets added with soluble and insoluble fibers extracted from O. ficus indica cladodes at early and late maturity stages, as the only source of calcium. The mineral content, bone mineral density (BMD), physical, microstructural, and biomechanical properties of rat femurs were determined. The bones of rats fed with diets containing a soluble fiber extracted from O. ficus indica at early and late maturity stages exhibited better bone properties (resistance to fracture, microarchitecture, and calcium content) than control rats and rats fed with an insoluble fiber from O. ficusindica cladodes at both maturity stages. As expected, based on these results, the BMD values were higher in adolescent and pubertal rats fed with a diet containing the O. ficus indica soluble fiber. These results demonstrate that the soluble fiber from O. ficus indica cladodes is indeed a valuable source of bioavailable calcium, which contributes to improve physical, densitometric, biomechanical, and microstructural properties of bone in growing rats.

Calcium Bioavailability of Opuntia ficus-indica Cladodes in an Ovariectomized Rat Model of Postmenopausal Bone Loss

Osteoporosis is a disease of the skeletal system characterized by low bone mass and bone weakening, which increase the risk of fracture. This disease is associated with menopause because hypoestrogenism induces the maturation and activation of osteoclasts. In addition, a low dietary intake of calcium leads to low bone mineral density and postmenopausal osteoporosis. The objectives of this work were to determine calcium bioavailability of Opuntia ficus-indica cladodes at a late maturity stage and to assess its contribution in improving bone health in an ovariectomized rat model. Two-month-old Wistar female rats (n = 35) were used and distributed in seven experimental groups: (i) control group (Crtl), (ii) sham group (SH), (iii) ovariectomized group (OVX), (iv) ovariectomized group supplemented with calcium citrate (CCa), (v) ovariectomized group supplemented with O. ficus-indica powder (NI), (vi) ovariectomized group supplemented with soluble fiber from O. ficus-indica (FS) and (vii) ovariectomized group supplemented with insoluble fiber from O. ficus-indica (FI). Our results showed that calcium in the soluble fiber of O. ficus-indica is bioavailable and contributes to improve the physical, densitometric, biomechanical and microstructural properties of bones in ovariectomized rats. These findings indicated that O. ficus-indica cladodes at a late maturity stage represent a good source of bioavailable calcium and consumption of these cladodes might be beneficial for the prevention of osteoporosis and other bone diseases.