|Mineral Balance: Calcium- |
Minerals are more than just rocks that come from the earth and, ultimately, return there. They compose about four percent of the human body and must be obtained from what we eat and drink. We need only small amounts of minerals, but when they are lacking, either singly or in a partnership, things can happen in the body, from something as relatively minor as a muscle cramp to something more significant like osteoporosis. Minerals work together synergistically to perform a variety of functions. Some maintain pH balance; others facilitate the transfer of nutrients across cell membranes or help to conduct nerve transmissions. Still others control muscle contraction and relaxation. Some serve in both structural and functional capacities, such as calcium, magnesium and phosphorus.
Calcium’s best-known work is in the formation of bone and teeth, but it also plays a role in keeping the heart and muscles working the right way by governing contractions. Magnesium, a shiny metal that burns with a violent white light, is also a constituent of bone, but serves, too, as the principal player in more than three hundred enzyme reactions, while controlling potassium and calcium uptake, assisting nerve electrical activity, and managing the metabolism of carbohydrates. Mention burning, and phosphorus enters the conversation as the most fiery mineral. In the body, phosphorus is second in abundance only to calcium, and is necessary for bone growth, kidney function, cellular health and acid-alkaline balance.
Calcium and magnesium are classified as alkaline earth metals, having an oxidation number of +2, making them very reactive and, therefore, not found free in nature. They’re always combined with something else. Being metals, they have luster, and they conduct heat and electricity, a trait not shared with phosphorus, a brittle non-metal that also is neither malleable nor ductile. We’ll look at these more closely, one at a time.
Calcium is the most common mineral in the body, about 99% of which is in bones and teeth, the remainder being in the blood and soft tissue, where concentration range is narrow to facilitate bodily functions. This is so important that the body will pull calcium from bones to maintain other levels if calcium intake is insufficient. If you want a strong skeleton, calcium intake is critical. This is where thoughts of calcium usually stop. However, calcium also mediates constriction and relaxation of blood vessels and the transmission of some nerve impulses. There’s more to this, but we’ll table that for now, except to add that calcium is needed to activate blood clotting factors. Because of its vital nature, calcium levels need to be kept stable. That sodium compromises such stability is not well enough known. Too much sodium increases the loss of calcium in the urine, probably because of competition for reabsorption in the kidneys (Devine, 1995). Although we think that calcium supplements will do the trick, absorption is an issue. The maximum dose of elemental calcium that should be taken at one time is around 500 mg. More than that will not be beneficial, and may even backfire as constipation or gastric distress (Straub, 2007). As an aside, there is no definitive association of supplemental calcium with increased risk of kidney stones (Straub, 2007). Without a supplement, most Americans fail to meet the adequate intake for calcium.
Whether or not a comparatively high protein diet interferes with calcium metabolism is still a hot topic, based partly on the thoughts that the strongest bones belong to those cultures that lack the superfluity of animal protein enjoyed by industrialized nations.
Of the magnesium in the body, more than 60% is in the skeleton, about a fourth in muscle, and most of the remainder inside the cells. Structurally, you can find it in chromosomes and cell membranes, besides the bones (Rude,2006). It’s absolutely required for nucleic acid and protein synthesis, and for cell signaling. Working with calcium, the magnesium that sits outside cells plays a role in wound healing. To some of us, its role in the prevention of—and even the control of—high blood pressure is its most valued raison d’être.
Food sources of magnesium, from which overdose is not likely, include whole grains, nuts and leafy vegetables, among others. Supplementally, the citrates, glycinates and gluconates are well absorbed. Oxides and carbonates are not. The hydroxide form is used to make antacids. Traditionally, the balance of calcium to magnesium in a supplement has been about 3:1 or 2:1. Unless the cellular status of minerals is actually measured, it’s nearly impossible to predict what effect supplementation will have on a person’s mineral levels and ratios. There are too many variables to establish a fixed mineral ratio for everyone—organ health, infections, drug use, kidney and gut condition, and even hormonal factors. Little understood is that magnesium helps convert vitamin D into its active form so it can aid calcium absorption. Supplements that are high calcium-low magnesium may do less good than originally thought, since calcium and magnesium are two sides of a coin. Calcium must be balanced by magnesium, lest it harm cells and find itself the culprit in the etiology of disease (Rosanoff, 2012). Most Americans are magnesium shy, so the 2:1 ratio, Ca to Mg, will pay off.
A couple of decades ago, considerable emphasis was placed on calcium-phosphorus ratio, especially for infants. That may apply to conditions of rapid growth, but probably is irrelevant to adults because the nutrients will no longer be converted to tissue mass. The ratio of calcium to phosphorus may be of limited benefit, then, while absolute values are not. If ever the ratios held value, it was in the context of bone building, where Ca:P is close to 1.5:1. As phosphate in body fluids, the proportional relationship is about 2.2:1. But that doesn’t mean ratios are important throughout a person’s lifetime because phosphorus intake is likely to result in a surplus, since adults eat for energy rather than for growth and development.
Every cell in the body needs phosphorus, where it resides as phosphate (PO4), though mostly in bone as hydroxyapatite—Ca5(PO4)3(OH). Phosphorus, as phospholipid, makes up the cell membrane and, in other compounds, provides energy as adenosine triphosphate. In a diet low in magnesium, the ingestion of high amounts of fructose will compromise and lower phosphorus levels, upsetting acid-base balance and increasing urinary loss (Milne, 2000). Phosphorus is absorbed in the small intestine; excess is taken up by the kidneys. Increased intake of phosphorus as phosphoric acid from soft drinks and phosphate additives in a number of foods is a topic of recent concern. High phosphate reduces the formation of the active form of vitamin D (calcitriol) in the kidneys and reduces blood levels of calcium. Whether or not this affects bone mineral density is not an issue if there is adequate calcium and magnesium in the diet (Grimm, 2001).
Because it’s a critical component of living things, phosphorus is found in most foods, animal products being the best sources. In plant seeds (beans, nuts, grains), phosphorus is present in a storage form called phytate, from which only half the phosphorus is bioavailable because humans lack the enzyme needed to liberate it. It takes a lot to produce toxicity, which causes calcification of soft tissue and consequent organ damage, especially of the kidneys. A caveat in this regard is to keep an eye out for phosphate-containing laxatives, particularly those given prior to a colonoscopy.
It’s been said that life is all about balance. The harmonious arrangement of dietary and supplemental macro- and micro-nutrients is too important to discount. Too much protein for example, common to the Western World, could threaten calcium-magnesium-phosphorus equilibrium (Kitano, 1988), a condition deserving closer scrutiny (Moe, 2008) (Hegsted, 1981) (Baker, 2002) and presented with increased frequency in hospitalized patients (Ghosh, 2008).
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