Calcium & Bone Health

“Drink up your milk to grow big and strong”, was a common phrase uttered just a few decades ago, but does it hold merit? Is calcium related to bone health? If so, how much and why? Find out here.

Are calcium & bone related?

Yes, as 99% of the body’s calcium is stored in bone – we will understand this more in the physiology section [1].

How much calcium for optimal bone health?

The recommendations set by a variety of institutions are a bit different, but consuming 800 – 1200 mg/day, as an adult, is largely correct [1][2]. Also, oddly enough, although other molecules can be taken as supplements, ingesting calcium supplements seems to have little effect, likely due to the lowered transit time when not taken with food, the high dose in a single ingestion, and most importantly, the failure to pair it with other micronutrients vital for bone health (i.e. vitamin D, phosphorus, etc.) [7]. However, the supplementation of hydroxyapatite complexes (including phosphorus, magnesium, type 1 collagen, and other necessary units) showed differences in bone mineral density [8][9]. So, calcium alone may not do much, except if it is ingested as a complex with other minerals and vitamins.

Understanding the Physiology

Calcium, when ingested, is absorbed throughout the small intestine, but using different absorption patterns based on the amount ingested. If little is found in the chyme, then the calcium is absorbed through active transport across the epithelial cell wall of the duodenum, through a calcium transporter (CaT1) [10]. If calcium levels are high, then it moves through, in the ileum, via passive diffusion [10]. This is also all dependent on how reactive the intestinal peristalsis is, as with high concentrations, it tends to be extremely active, allowing high amounts of calcium to be in contact with the intestinal border for only a few minutes at a time [10]. Vitamin-D dependent calbindin protein is synthesized within the epithelial cells and binds to calcium that enters the cell, keeping free levels low, and allowing diffusion to occur more readily [10]. Then, calcium is either released attached to other ions, to albumin, or free in serum and finds its way to bone, where it is absorbed by the cells [11][12].

Bone is not, as many might believe, solely made up of calcium [1]. Bone is made up of molecules known as hydroxyapatite (made up primarily of calcium and phosphate), collagen osteoid, and glycoproteins [1]. Hydroxyapatite contains 99% of the calcium in the body [6].

In terms of the using of hydroxyapatite, osteoblasts (bone forming cells) synthesize it and stitch it together to form bone structure [1][4]. They also produce the initial scaffolding needed to fill, made of type 1 collagen [5]. Once the osteoblasts have produced collagen, the collagen is twisted and linked together into helical fibrils and stacked longitudinally, as well as in cross sections; once this framework is created, osteoblasts deposit the hydroxyapatite to fill the gaps between the collagen, and bone is then formed [5].

Summary

In summary, calcium is imperative for bone health, but calcium alone is almost useless. You need to be consuming adequate vitamin D, as well as the other units that make up bone, for calcium to have value in bone health.

Writer: Nicolas Verhoeven
References
[1] Flynn, A. (2003). The role of dietary calcium in bone health. The Proceedings of the Nutrition Society, 62(4), 851-8. doi:10.1079/PNS2003301

[2] Office of Dietary Supplements - Calcium. (2017, March 2). Retrieved from https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/

[3] Blair, H. C. (2017). Osteoblast Differentiation and Bone Matrix Formation In Vivo and In Vitro. Tissue Engineering, 23(3). Retrieved from https://doi.org/10.1089/ten.teb.2016.0454

[4] Florencio-Silva, R. (2015). Biology of Bone Tissue: Structure, Function, and Factors That Influence Bone Cells. BioMed Research International. Retrieved from http://dx.doi.org/10.1155/2015/421746

[5] Ott, S. (2003). ASBMR educational materials. Retrieved from https://depts.washington.edu/bonebio/ASBMRed/matrix.html

[6] Ross, A. C. (2011). Dietary Reference Intakes for Calcium and Vitamin D. In Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK56060/

[7] Reid, I. R. (2014). Should We Prescribe Calcium Supplements For Osteoporosis Prevention? Journal of Bone Metabolism, 21(1), 21. doi:10.11005/jbm.2014.21.1.21

[8] Ciria-Recasens, M., Blanch-Rubió, J., Coll-Batet, M., Del Pilar Lisbona-Pérez, M., Díez-Perez, A., Carbonell-Abelló, J., … Pérez-Edo, L. (2011). Comparison of the Effects of Ossein-Hydroxyapatite Complex and Calcium Carbonate on Bone Metabolism in Women with Senile Osteoporosis. Clinical Drug Investigation, 31(12), 817-824. doi:10.1007/bf03256920

[9] Castelo-Branco, C., & Dávila Guardia, J. (2014). Use of ossein–hydroxyapatite complex in the prevention of bone loss: a review. Climacteric, 18(1), 29-37. doi:10.3109/13697137.2014.929107

[10] Bronner, F. (2002). Mechanisms of intestinal calcium absorption. Journal of Cellular Biochemistry, 88(2), 387-393. doi:10.1002/jcb.10330

[11] Besarab, A., DeGuzman, A., & Swanson, J. W. (1981). Effect of albumin and free calcium concentrations on calcium binding in vitro. Journal of Clinical Pathology, 34(12), 1361-1367. doi:10.1136/jcp.34.12.1361

[12] Kennedy, P. (n.d.). Calcium homeostasis and osteoporosis | McMaster Pathophysiology Review. Retrieved from http://www.pathophys.org/osteoporosis/

 

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