The Chemistry Column

Beyond the bones

Claire Gormley

Whenever I hear ‘Calcium’ my mind immediately jumps to ‘strong bones’. That’s thanks to the highly successful Got Milk? advertisement campaign I was exposed to, growing up in the United States. I’m sure I am not alone in this. Got Milk?, along with many precursor campaigns, convinced us that the key to developing a healthy skeletal system was a daily dose of Calcium from the carton of milk on our lunch trays. It was only recently that I learned the truth behind the suggestion that drinking milk is the best way to build strong bones: the advertising campaign was designed to increase consumer demand, so that processed dairy products could be shipped to soldiers abroad (Belluz, 2015). In fact, portions of almonds, bok choy, broccoli and kale can each provide our body with more Calcium than a glass of milk, but we rarely consider these other sources because the association between Calcium and milk is so strong (Cormick and Belizán, 2019; Belluz, 2015). Now that the mental knot tying Calcium to milk has been loosened, I begin to wonder— how does Calcium contribute to our bodies beyond building strong bones?

Calcium belongs to the Alkaline Earth Metals— Group two in the Periodic Table of Elements —along with Beryllium, Magnesium, Strontium, Barium and Radium. Alkaline Earth Metals are all shiny, silvery-white in their solid state. Like all the others, Calcium gives away its two outermost electrons, also known as its valence electrons, to achieve its most stable form. The loss of electrons, which are negatively charged particles, creates an overall positively charged atom, also known as a cation. The Calcium cation, Ca2+, is incredibly important for plant growth and development and cell wall formation, as well as for sending intracellular messages (Helper, 2005; White and Broadly, 2003; National Institutes of Health, 2021).

About 99% of the Calcium in our bodies is stored in our bones and teeth, providing them with structure and strength, hence the need to get enough Calcium in our diet to build strong bones (Lewis III, 2021; Harvard, 2021). The other 1% is needed by the blood to stimulate blood clot formation, as well as by muscle cells and neurons to activate specific cell functions (Singh et al, 2019; Lewis III, 2021). If these parts of our body are not getting sufficient Calcium, a hormone called parathyroid— one of two hormones that regulate the level of Calcium in our blood —is produced to signal our body to preserve Calcium and to stimulate our bones to release some of their stored Calcium for the blood, muscles, and neurons to use (Lewis III, 2021).

In muscle cells, Calcium is required for contraction. The mechanisms that achieve this, known as voltage-gated channels, are utilised by many different types of cells to perform different functions. Because Calcium is found in higher concentrations outside of muscle cells— in the extracellular fluid —the process involves a build-up of positively charged ions (Ca2+) on one side of a membrane to create a concentration gradient. Contraction of the muscle is dependent on the Calcium outside the cell flowing into the cell, but this is not as simple as it sounds (Kuo and Ehrlich, 2015; Helper, 2005). In order for Calcium to enter the cell, neurotransmitters must first bind to receptors on the surface of the muscle cell (another process dependent on the Calcium in our neurons). The binding of the neurotransmitter causes the cell membrane to depolarise, to rapidly switch off the positive and negative charges on either side of the cell membrane. The depolarisation causes specific Calcium protein channels— called L-type Ca2+ channels, located within the cell membrane —to open, allowing Calcium to flow into the cell. In turn, this influx of Calcium opens a larger Calcium channel located inside the cell (in the membrane of the sarcoplasmic or endoplasmic reticulum, depending on what type of muscle is contracting). These organelles store Calcium, so when the channels are opened the concentration of Calcium within the cell increases even further. After Calcium levels are raised inside the cell, Calcium binds to actin or calmodulin— two proteins found in striated or smooth muscles, respectively — and subsequent actions for contraction take place (Kuo and Ehrlich, 2015).

So, Calcium kickstarts a multitude of cellular processes in both plants and animals. Its ability to perform so many crucial roles for life is truly unique. Other cations, such as magnesium (Mg2+), have much stricter requirements for binding and are therefore more limited in the processes they can assist (Brini et al, 2014).

Thankfully, I now know more than one place where I can find the Calcium I need. Bring on the bok choy!

References

Belluz, J. (2015) ‘How we got duped into believing milk is necessary for healthy bones’, in Vox. [Accessed 10 November 2021]. https://www.vox.com/2015/4/19/8447883/mi lk-health-benefit.

Brini, M.; Calì, T.; Ottolini, D., and Carafoli, E. (2014) ‘Neuronal Calcium signaling: function and dysfunction’, in Cellular and Molecular Life Sciences, 71:2787-2814.

Cormick, G., and Belizán, J. M. (2019) ‘Calcium Intake and Health’, in Nutrients, 11(7):1606.

Helper, P. K. (2005) ‘Calcium: A Central Regulator of Plant Growth and Development’, in Plant Cell, 17(8): 2142-2155

Kuo, I. Y., and Ehrlich, B. E. (2015) ‘Signaling in Muscle Contraction’, in Cold Spring Harbor Perspectives in Biology, 7(2): a006023.

Lewis III, J. L (2021) ‘Overview of Calcium’s Role in the Body’, in MSD Manual [Last modified October 2021].

National Institutes of Health (2021) ‘Calcium’. U.S. Department of Health and Human Services. [Accessed 10 November 2021]. https://ods.od.nih.gov/factsheets/CalciumConsumer/

Singh, S.; Dodt, J.; Volkers, P.; Hethershaw, E.; Philippou, H.; Ivaskevicius, V.; Imhof, D.; Oldeenburg, J., and Biswas, A. (2019) ‘Structure functional insights into Calcium binding during the activation of coagulation factor XIII A’, in Scientific Reports, 9: 11324

White, P. J., and Broadley, M. R. (2003) ‘Calcium in Plants’, in Annals of Botany, 92(4):487-511