16.11: Summary

Minerals are inorganic substances, some of which we require in small amounts. Those described as major minerals have an adult recommended intake of more than 300 mg per day, and include calcium, phosphorus, magnesium, sodium, potassium, and chloride.

Bones and teeth contain most of the body’s calcium, and seem like a separate structural part of our body, like the Halloween skeleton. But calcium and other minerals move in and out of bone all the time. In fact, bone serves as a mineral reserve whenever dietary intake is low.

In the blood, calcium levels are kept constant by the hormones calcitonin and parathormone. A drop in blood calcium levels can cause tetany; levels are affected by these calcitonin and parathormone, not by diet. Low levels of dietary calcium will result in calcium being taken from bone.

Low calcium content in the bone leads to osteoporosis—brittle, easily broken bone. Many factors affect the risk of osteoporosis, including gender, family history, race, and body weight. Smoking and alcohol, along with low dietary intake of calcium, increase risk of osteoporosis. Other nutrients such as phosphorus and vitamin D also have an effect. Stress-bearing exercise strengthens bones, and estrogen-replacement or bisphosphonate therapy can prevent or delay osteoporosis for postmenopausal women.

It’s important to get enough calcium during growth, when bones are developing. Most of our calcium comes from milk products, but there are other foods that have significant amounts. It’s best to get calcium from foods, since supplements may cause other health problems, and natural supplements (e.g., bone meal) can be contaminated with lead or other toxins.

Phosphorus is found in bones and teeth, but also in phospholipids and other molecules (e.g., DNA, RNA, ATP). A deficiency is unlikely under normal circumstances (it has been found in premature infants fed only breast milk, and after long use of aluminum hydroxide as an antacid).

Magnesium is required for many cell functions. It’s hard to become deficient, and toxic amounts come from magnesium-containing medications rather than food.

Sodium, chloride, and potassium are called electrolytes because they dissolve into charged particles that conduct electrical current. Potassium is mostly found inside cells (intracellular), whereas sodium and chloride are mostly found outside cells (extracellular). Electrolytes help regulate water movement, and transmit electrical impulses in nerve and muscle cells.

An adequate intake of sodium for those over age 13 is 1500 mg per day. The typical American diet contains more than twice as much and increases the risk of high blood pressure and chronic disease. The CDRR (Chronic Disease Risk Reduction Intake) for sodium is 2300 mg, i.e., if your intake is higher than this, reducing your intake reduces your risk of chronic disease. Sodium is excreted in urine, and to some extent in perspiration; sodium levels are regulated by the kidney. Deficiency can occur after heavy and prolonged sweating, or from certain diseases.

Chloride parallels sodium intake and is important in water regulation and nerve function and is a component of stomach acid (hydrochloric acid). Deficiency and toxicity are rare.

Potassium is important for electrical impulses in the heart, and also cell metabolism, and may be protective against high blood pressure. Deficiency can be caused by drugs, diarrhea or vomiting, or bulimia. Toxicity is rare, but can affect the heart.

For continually updated fact sheets on individual minerals, go to the website of the Office of Dietary Supplements. ods.od.nih.gov/factsheets