Introducing the major minerals

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The following major minerals are essential for human beings:

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Calcium

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Phosphorus

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Magnesium

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Sulfur

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Sodium

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Potassium

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Chloride

Note: Sodium, potassium, and chloride, also known as the principal electrolytes, are covered in Chapter 13.

Although sulfur, a major mineral, is an essential nutrient for human beings, it's almost never included in nutritional books and/or charts. Why? Because it's an integral part of all proteins. Any diet that provides adequate protein also provides adequate sulfur. (For more on proteins, bookmark this page and turn back to Chapter 6.)

After you've checked out proteins, come on back to look at the major minerals in minute detail.

An elementary guide to minerals

The early Greeks thought that all material on Earth was constructed of a combination of four basic elements: earth, water, air, and fire. Wrong. Centuries later, alchemists looking for the formula for precious metals, such as gold, decided that the essential elements were sulfur, salt, and mercury. Wrong again.

In 1669, a group of German chemists isolated phosphorus, the first mineral element to be accurately identified. After that, things moved a bit more swiftly. By the end of the 19th century, scientists knew the names and chemical properties of 82 elements. Today, 112 elements have been identified.

The classic guide to chemical elements is the periodic table, a chart devised in 1869 by Russian chemist Dmitri Mendeleev (1834-1907), for whom mendelevium was named. The table was revised by British physicist Henry Moseley (1887-1915), who came up with the concept of atomic numbers, numbers based on the number of protons (positively charged particles) in an elemental atom.

The periodic table is a clean, crisp way of characterizing the elements, and if you are now or ever were a chemistry, physics, or premed student, you can testify firsthand to the joy (maybe that's not the best word?) of memorizing the information it provides. Personally, I'd rather be forced to watch reruns of The Dating Game.

Calcium

When you step on the scale in the morning, you can assume that about three pounds of your body weight is calcium, most of it packed into your bones and teeth.

Calcium is also present in extracellular fluid (the liquid around body cells), where it performs the following duties:

1 Regulating fluid balance by controlling the flow of water in and out of cells 1 Enabling cells to send messages back and forth from one to another 1 Keeping muscles moving smoothly and preventing cramping

An adequate amount of calcium is important for controlling high blood pressure — and not only for the person who takes the calcium directly. At least one study shows that when a pregnant woman gets a sufficient amount of calcium, her baby's blood pressure stays lower than average for at least the first seven years of life, meaning a lower risk of developing high blood pressure later on.

Your best food sources of calcium are milk and dairy products, plus fish such as canned sardines and salmon. Calcium also is found in dark green leafy vegetables, but the calcium in plant foods is bound into compounds that are less easily absorbed by your body.

Calcium: The bone team player

The toe bone's connected to the foot bone. The foot bone's connected to the anklebone. The anklebone's connected to the knee bone. And what holds them together all the way up to the head bone is connected to your diet.

Like all body tissues, bones are constantly being replenished. Old bone cells break down, and new ones are born. Specialized cells called osteoclasts start the process by boring tiny holes into solid bone so that other specialized cells, called osteoblasts, can refill the open spaces with fresh bone. At that point, crystals of calcium, the best-known dietary bone builder, glom onto the network of new bone cells to harden and strengthen the bone.

Calcium begins its work on your bones while you're still in your mother's womb. But it's not the only mineral at play. You should also think zinc. Based on a survey of 242 pregnant women in Peru, where zinc deficiency is common, Johns Hopkins researchers found the babies born to women who got prenatal supplements with iron, folic acid, and zinc had longer, stronger legs bones than did babies born to women who got the same supplement minus the zinc.

After you're born, calcium continues to build your bones, but only with the help of vitamin D, which produces a calcium-binding protein that enables you to absorb the calcium in the milk Mummy feeds you. To make sure you get your D, virtually all milk sold in the United States is fortified with the vitamin. And because you may outgrow your taste for milk but never outgrow your need for calcium, calcium supplements for adults frequently include vitamin D.

But vitamin D isn't milk's only contribution. Remember the iron in the Peruvian (and

American) prenatal supplements? It isn't there by accident. Iron increases the production of collagen, the most important protein in bone. Milk contains lactoferrin (lacto = milk; ferri = iron), an iron-binding compound that stimulates the production of the cells that promote bone growth.

When researchers at the University of Auckland in New Zealand added lactoferrin from cow's milk to a dish of osteoblasts, the bone cells grew more quickly. When they injected lactoferrin into the skulls of five lab mice, the bone at the site of the injection also grew faster, leading the team to suggest in the journal Endocrinologythat lactoferrin may play a role in treating osteoporosis.

No surprise to the Department of Nutrition Sciences at the University of Arizona, where a study done with scientists from the University of Arkansas and Columbia University shows that women in their 40s, 50s, and 60s who get about 18 milligrams of iron a day have stronger, denser bones than women who get less iron. What makes this intriguing is that 18 milligrams a day is more than double the current RDA (8 milligrams) for older women.

But the iron/calcium dance is a balancing act. In your body, iron and calcium appear to compete to see which one gets absorbed. So the extra iron works only for women who get about 800 to 1,200 milligrams calcium a day — women who get less and women who get more don't seem to benefit from extra iron.

Finally, please note that the word bones begins with b — as in vitamin B12. The female sex hormone estrogen preserves bone; the male sex hormone testosterone builds new bone. As people age and their supply of sex hormones diminishes, they lose bone faster than they can replace it. One complicating factor may be low levels of vitamin B12. A report in the Journal of Clinical Endocrinology and Metabolism says that researchers at the University of California, San Francisco, found that women with lower levels of this vitamin also have less dense hip bones.

So to protect your bones, you need calcium, zinc, iron, and vitamins D and B12, all found most abundantly in milk, cheese, eggs, and red meat. Which sounds like a cardiologist's nutritional high-fat, high-cholesterol nightmare — unless you edit the menu to read: skim milk, low-fat cheese, egg whites, and lean beef. Way to go.

Phosphorus

Like calcium, phosphorus is essential for strong bones and teeth. For tiptop performance, you need about half as much phosphorus as calcium. Phosphorus also enables a cell to transmit the genetic code (genes and chromosomes that carry information about your special characteristics) to the new cells created when a cell divides and reproduces. In addition, phosphorus

1 Helps maintain the pH balance of blood (that is, keeps it from being too acidic or too alkaline)

1 Is vital for metabolizing carbohydrates, synthesizing proteins, and ferrying fats and fatty acids among tissues and organs

1 Is part of myelin, the fatty sheath that surrounds and protects each nerve cell

Phosphorus is in almost everything you eat, but the best sources are highprotein foods such as meat, fish, poultry, eggs, and milk. These foods provide more than half the phosphorus in a nonvegetarian diet; grains, nuts, seeds, and dry beans also provide respectable amounts.

Magnesium

Your body uses magnesium to make body tissues, especially bone. The adult human body has about an ounce of magnesium, and three-quarters of it is in the bones. Magnesium also is part of more than 300 different enzymes that trigger chemical reactions throughout your body. You use magnesium to

1 Move nutrients in and out of cells 1 Send messages between cells

1 Transmit the genetic code (genes and chromosomes) when cells divide and reproduce

An adequate supply of magnesium also is heart-healthy because it enables you to convert food to energy using less oxygen.

Bananas are a good source of magnesium and so are many other plant foods, including dark green fruits and vegetables (magnesium is part of chlorophyll, the green pigment in plants), whole seeds, nuts, beans, and grains.

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