2.12a The Minerals: Introduction and Calcium

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2.12a: Minerals: Introduction and Calcium - Update 06 December 2021

A Mineral is a chemical compound of a metal atom. The metals in food are attached to one or more of the chemical gas atoms (e.g., Na⁺Cl^–, usually written NaCl, it is common table salt). The minerals in foods are sometimes attached to proteins, fats or carbohydrates and then, in the stomach, need to be digested away from the attachment.

   Some minerals, such as the metals, lead (Pb from the Latin Plumbum)  or Arsenic (As), are toxic. The minerals appear here first major then minor, and each in alphabetic order.

Calcium Ca

Calcium is in Group 2 of the Periodic Table, the alkaline earth metals that include beryllium Be, magnesium Mg, strontium St, barium Ba and radium Ra. The ⁴⁰Ca (superscript 40 before the Ca is the atomic mass to nearest integer) nucleus has 20 protons and 20 neutrons, the outer orbital reactive electrons are 2 and calcium’s ionic form, is Ca²⁺. Calcium is found in nature combined with oxygen (O) as quicklime CaO. It is mostly in Calcium carbonate (CaCO3, from CaO combined with carbon dioxide CO2). Dietary sources are bone, milk and seafood especially in shrimp outer shell. So chew the outer shell carefully and swallow it.

Functions and Toxicities: Calcium supplies the Ca in calcium phosphate for rigid structure in bone and cartilage of skeleton. The Ca²⁺ is also very important in nerve transmission in brain, in regulation of heart rate and in muscle contraction. Too low Ca²⁺ in blood in alkaline pH (after a heavy meal) causes the muscle spasm of leg calf pains that bother you in bed at night. Too high Ca²⁺ causes weak muscles and also calcification and hardening in tissues, especially bad in arteries. Also actions on brain neurons and heart muscle electricity based on small changes in cellular fluid concentrations. The Ca²⁺ levels inside brain cells are so important to the thinking process that the popular calcium-channel-blocker medication should be carefully considered and best replaced when possible (guided by expert opinion) by the beta-blocker.

Blood Calcium is so important to life that the body regulates it in a narrow normal concentration range. Dangerously low blood calcium (less than 8 mg/dL, or 2.0 mM/L) hypocalcemia induces a state of tetany, which is painful repetitive muscle contractions. The condition is also seen in the end stage of renal failure. Dangerously high blood calcium (more than 10 mg/dL, or 2.5 mM/L) hypercalcemia, seen with metastatic cancer, sarcoidosis, hyperparathryoidism and overdose vitamin D, causes disastrous calcification all over the body and heart arrythmias and sleepiness verging on coma. 

Regulation of blood calcium ion [Ca²⁺] is by parathyroid hormone (PTH). When blood plasma [Ca²⁺] falls, the parathyroid glands (Several in front neck) get stimulated to return blood calcium to normal. The PTH raises blood [Ca²⁺] by causing it to be leached out of bone, by also stimulating kidneys to lose more phosphate [as HPO₄^–2 & PO₄^–3] in urine, and by activating kidney production of vitamin D to increase absorption of calcium in food from intestine. Once blood [Ca²⁺] rises to normal concentration, the PTH is shut off. An early sign of low Ca in diet is your blood testing high PTH and borderline low-normal Ca. Next read how it happened to me.

My Calcium Dietary Deficiency: In 2004, I got a bone density x-ray to check osteoporosis. It showed bone density normal for my then age 71. But in 2006 it dropped off the normal line into risk for fracture. Something was taking calcium out of my bones! So I had a fasting blood sample drawn: The blood calcium concentration [Ca] was 8.5 mg% (low-normal), the inorganic phosphorus was normal, the serum vitamin D was normal, but the parathyroid hormone (PTH) was increased 50% above normal. It explained the loss of bone density. My calcium dietary deficiency had stimulated the parathyroid glands to over-produce PTH and it had caused the leach of calcium out of my bones. That showed up as the dangerously low bone density. If it continued, I’d end with a fractured hip. I started calcium carbonate 500 mg pill 3X a day with vitamin D 0.25 microgram. Two months later I had my blood re-checked. It showed a 1 mg/dL rise in [Ca] to 9.5 and a drop in PTH to normal value. It proved my hyperparathyroidism was secondary to calcium deficiency.

   Why the calcium deficiency? As part of my healthy eating I had neglected the major source of calcium in diet (milk), I heavily ate foods containing large amount of oxalate (greens) that block absorption of food calcium by intestines, and I drank lots of coffee and wine which cause calcium to be lost in urine. It resulted in the loss of calcium that must have been going on for years and stimulated my parathyroid glands to over-secrete PTH, and its effect was the leach of calcium from my bones and worsening of my aging osteoporosis as I found out, luckily, by the test rather than by a fractured hip.

Postscript: After years of the Ca and vit. D, I repeated my tests; they showed normal blood PTH and calcium and my osteoporosis reversed by the treatment.

Absorption of Ca from GI Tract and its Excretion: Calcium in food often is in protein complex. Digestion in stomach and upper intestine frees Ca for absorption. Calcium supplement pill CaCO₃ liberates Ca²⁺ in stomach acid juice and it is absorbed in small intestine best with Ca in food. Also, if you need to take iron pills for your blood anemia, do not take the iron pill with calcium pill.

Excretion of calcium is via kidneys in urine. With high calcium in blood, the [Ca²⁺] in urine may exceed solubility of its phosphate and urate, causing kidney stone. Taking 500 mg calcium pills at the same time as high dose vitamin C causes calcium salts to form stones in the acid urine caused by vitamin C pill. But a high water intake prevents Ca kidney stone. So drink a lot of water every day.

Dietary Consideration: Keeping good sources of Ca in diet is to prevent osteoporosis which is now epidemic in post-menopausal woman and frequent in men over 70.  Today we humans depend mostly on dairy (milk and its product) for calcium, which, in the US is estimated to supply 72% dietary Ca. But the usual supermarket milk has too much sodium (Na⁺) and cholesterol. So if you wish to depend on milk for your calcium be sure to buy low-Na, low-fat milk product.

Food Source & Bioavailability: Best source of food Ca with highest bioavailability is bone, cartilage and milk & dairy product; worst is cereal and green vegetables like spinach, high in phytate (cereals) and oxalates (greens) that make insoluble un-absorbable complexes with calcium. Many foods are fortified with calcium. Look at food labels for amounts. 

Because human food is poor in Ca, and because dairy is not ideal food as we age, many older persons will depend on calcium carbonate (CaCO_{3; or other Ca compound like Ca gluconate}) 500 mg pill to prevent osteoporosis. Taking Ca pills regularly may harden stool causing constipation. Eating mango and other fruits and yogurt will prevent it but also, if one has the problem, finger removal of stool through anus is easy and a good health behavior because it prevents dangerous straining at stool.

If you take vitamin D, it should be 0.25 microgram (10 IU) vitamin D with each 500 mg calcium carbonate pill and blood calcium should be checked at intervals and if rising much above 9.0 mg%, or 2,25 mM/L, stop it. 

Risks of Low Calcium Food Intake: Beyond osteoporosis, not eating enough Ca is a factor of several disorders. It has been shown that sufficient calcium protects against or reduces risk of hypertension (High arterial blood pressure), colon cancer, lead poisoning and kidney stone.

Requirement: See www.cc.nih.gov/ccc/supplements. Ca is a plateau nutrient; above a certain intake, there is little further increase in Ca retention because the excess spills over into urine. But the Ca in usual food intake of the US is not enough to prevent osteoporosis, especially for women in the lower range of average Ca intake. Rely on food calcium to correct this.

             Continues Next Section, click 2.12b Chromium, Copper and Iodine - Nutrition & T...