What They Are and Why You Need Them
By Denis Faye

In October we evaluated vitamins. Now it's time to take on minerals.

The biggest difference between vitamins and minerals is that minerals aren't organic.

Also, you can actually absorb minerals through industrial contaminants in both the air and water, although that's not something we recommend.

There are two types of minerals: macro and trace. Macro minerals are required in quantities ranging from 100 milligrams (mg) to 1 gram. This group includes calcium, phosphorus, magnesium, sodium, potassium, chloride and sulfur. These are your body's major electrolytes, or salts. Although they serve various functions, they all work together to maintain and carry electricity across your body by way of your cells. As the folks at Gatorade love to warn us, you lose electrolytes when you sweat, so maintaining them is especially important for us exercise nuts. And this can be a little hard to gauge because the scale slides greatly. For example, an inactive person can live on 500 mg of sodium a day, but an athlete doing hard, prolonged activity (running in the desert, for example) can lose 2000 mg an hour!

The second group of minerals is called trace minerals. There are quite a few of these, but the ones we're going to deal with are copper, iodine, zinc, selenium, chromium and manganese. As their heading would indicate, you don't need much of these bad boys to get by. And like all minerals, too much can be toxic.

Magnesium
There's no recommended daily allowance (RDA) for magnesium, although roughly 400 mg is a healthy intake for men, and 300 mg for women. But like all electrolytes, more is needed when you exercise. Taking too much can lead to kidney problems, with side effects including nausea, vomiting, diarrhea, dizziness and muscle weakness. If you do ample exercise, this is generally not a problem.

Magnesium is the cattle dog of electrolytes, as it herds other electrolytes into and out of cells. This is why you'll so often see it mixed into various supplements. It also regulates energy production in cells and is vital for proper muscle, nerve and enzyme function. This makes it particularly important for exercise—low levels can lead to problems such as cramping.

Mostly found inside bones and cells, magnesium is plentiful in the body. It's absorbed through the small intestines and can be found in nuts, green vegetables, whole grains—and especially pumpkin seeds.

Zinc
You don't need much zinc—the RDA is only 15 mg. But those little milligrams go a long way. Zinc supports your immune system and aids in healing. It's also important for your digestion by stimulating approximately 100 enzymes—protein catalysts that convert nutrients to energy and break down food.

If you take over 150 mg a day on a regular basis, you run the risk zinc toxicity, a nasty bit of business involving reduced immune function and reduced levels of "good" cholesterol.

You'll find zinc in liver, eggs, seafood, whole grains and oysters, which contain an impressive 11 mg per gram.

Copper
With an RDA of 2 mg, you need just a hint of copper, but that hint is vital for forming red blood cells and making sure your immune system, bones, blood vessels and nerves stay healthy.

Too much copper, however, can be trouble. For adults, taking more than 10 mg a day can lead to toxic reactions including severe anemia, nausea, abdominal pain, diarrhea, coma and death.

Fortunately, it's hard to overdose on copper through a healthy diet. Usually the way it happens is through industrial contamination or overuse use of copper supplements.

Your best sources of copper include oysters, nuts, organ meats and legumes.

Manganese
There's no RDA for manganese, about roughly 2 mg is a good target.

Manganese helps form tendons and other connective tissue, fats, cholesterol, bones and proteins. It also aids in the digestion of certain proteins, as well as transporting glucose throughout the body.

It's not the most exciting mineral, considering that deficiency in humans has never been reported—nor has manganese toxicity from dietary intake. However, inhaling manganese-laced dust has been known to damage the central nervous systems of miners and steel workers.

Just in case, the Food and Nutrition Board of the Institute of Medicine says adults should keep their manganese intake to below 11 mg daily.

You'll find manganese in nuts, whole grains, vegetables, fruits and, apparently, mine shafts.

Chromium
Once again, there's no RDA for chromium, but 35 micrograms (mcg) per day is suggested for men, 25 mg for women.

Chromium works with insulin to aid cells in taking in glucose and releasing energy. People who primarily eat processed foods are strong candidates for chromium deficiency. Also, chromium is passed through urine, sweat, bile and hair, so people who do a lot of physical exercise need to keep an eye on their level. A deficiency is characterized by insulin resistance, hyperglycemia and lipid abnormalities.

There have been no known cases of chromium toxicity—not even in steel workers.

You'll find this mineral in broccoli, turkey, corn oil, clams, brewer's yeast and whole grains. So, if your kids resist eating broccoli, tell them it's okay, they can just eat clams instead.

Iodine
Checking in with an RDA of 150 mcg, iodine provides only one service for the human body, but that service is a doozy.�It helps in the formation of the all-important thyroid hormone, which is crucial for human growth and development.

Although iodine deficiency is rare nowadays, it can lead to goiter, a swelling of the thyroid gland that shows up on the front of the neck. Ironically, too much iodine over a long period of time can actually hinder thyroid function, which in turn leads to hypothyroidism and, you guessed it, again with the goiter.

According to the Food and Nutrition Board of the Institute of Medicine, iodine toxicity can be a risk for an adult when the approximately 1100 mg daily limit is exceeded. Although it would be hard to eat that much, our most common source of contact with iodine is car exhaust.

While you'll want to avoid sucking tail pipes, healthier sources of iodine are seafood and iodized salt.

Molybdenum
Although molybdenum has no RDA, the approximately 45 mcg you should be taking is needed to convert something called purine into uric acid. And why is that important? Because your body needs uric acid to take iron out of storage and put it in your blood.

Molybdenum plays a role in several other enzyme-related activities, but none of them are as sexy as that uric acid conversion.

Molybdenum deficiency isn't really a concern nowadays and toxicity is extremely rare, although if you do consume more than 2000 mcg a day it could interfere with your absorption of copper, or lead to nausea, diarrhea, or joint pain and swelling.

You'll find it in milk, dried beans, peas, nuts and seeds, eggs, liver, tomatoes, carrots and meats.

Selenium
There's no RDA for this mineral, but 55 mcg is a good number for most adults to shoot for. It plays an important role in antioxidant enzymes and is crucial if you want to keep your immune system and thyroid gland working properly.

Too much selenium, as in 750 mcg on a daily basis, can lead to selenosis, a condition with symptoms including nausea, vomiting, diarrhea, hair loss, white blotchy nails, and mild nerve damage. Selenosis is rare in America, usually resulting from industrial accidents.

Given its role in the immune system and as an antioxidant, researchers are currently investigating the effect of selenium supplementation on HIV patients.

You'll find selenium in seafood, organ meats, lean meats, grains—and huge doses in Brazil nuts, as in a quarter cup containing 1036 mcg.

Calcium
Calcium's 1000 mg RDA is an important one. When we hit 30, we start to lose bone mass. Getting enough calcium, vitamin D and phosphorus helps slow that bone loss down. It is also essential for preventing osteoporosis.

However, make sure to keep it below 2500 mg a day. Any more could lead to constipation and interfere with absorption of iron and magnesium.

Although it's widely believed that dairy is the source of calcium, in fact there are quite a few sources—many of which are more efficient than milk—including tofu and whole grains, cold-water fish, broccoli and spinach.

Iron
The RDA for iron is a paltry 18 mg, given that the adult body is pretty good at holding on to this mineral. The exception to this is menstruation. Since the bulk of your iron is stored in red blood cells, women with heavy periods experience significant iron loss.

Iron is an important component of two proteins, hemoglobin and myoglobin. Hemoglobin, found in red blood cells, carries oxygen to your body's tissues. The lesser-known myoglobin also helps provide oxygen to muscles.

Because we hold on to iron, it's an easy one to get too much of. For adults, 45 mg is a good number to keep below. Signs of iron toxicity include nausea, vomiting, constipation, diarrhea, dark-colored stools and abdominal distress.

There are two kinds of dietary iron: heme and nonheme. The body absorbs heme, which comes from meat, quite efficiently. Nonheme, from lentils and legumes, has a tougher time getting in.

Phosphorus
The RDA for phosphorus is 1000 mg. Although its main function is forming bones and teeth, it also plays an important part in the body's use of protein, carbs and fats for the growth and upkeep of cells.

The kidneys regulate the body's phosphorus, so you pass what you don't need. People with kidney problems need to limit phosphorus intake. Elevated phosphorus levels in the blood can lead to hyperphosphatemia, which means blood calcium levels decrease and the parathyroid gland overproduces parathyroid hormone, leading to bone loss.

But it's pretty tough to totally knock phosphorus from your diet since most foods contain this mineral, especially fish, meat, poultry, eggs and grains.

Potassium
There's no RDA for potassium, but if you eat a healthy, balanced diet, you should get plenty of it. Exercise can change this, as you lose it quickly when you sweat. Since sweat is approximately 3 parts sodium to 1 part potassium, it's good to keep that in mind when rehydrating during exercise.

You'll find potassium inside every cell in your body, where it balances the sodium outside the cells. The two maintain proper hydration. An imbalance can lead to pooling of water or dehydration.

As with phosphorus, the kidneys regulate your potassium, so if you get too much, it comes out in your urine.

Potassium sources include lean meats, vegetables and fruit.

Sodium
Many of us mistake this important electrolyte for a villain. Indeed, too much sodium can lead to hypertension, edema and even osteoporosis. But don't blame this poor mineral! Instead, blame our lousy eating habits. The RDA for sodium is less than 2400 mg a day. The average American diet provides twice that.

Like with potassium, when we sweat, the amount of sodium we need changes rapidly. Your body only needs around 500 mg a day to function properly, so the RDA is based on a ballpark estimate. If you sit around all day, you need less. If you're a bike messenger in the tropics, chances are you'll need a lot more. In an average hour of exercise, like a session of Burn It Up!, you probably sweat out about 600 mg of sodium, and this can double if it's hot outside.

Sodium is crucial because it works with potassium to maintain the body's extracellular fluid levels by pumping water into cells. It also plays an important role in several other functions, including regulation of plasma volume, nerve impulses and muscle contractions.

Fortunately for Americans, the body can pass excess sodium through the kidneys. Also, as mentioned earlier, we sweat out lots of the stuff during exercise, so it's important to find a balance that's right for you.

The best way to get sodium is through salt and all that is salty. Some healthier examples of high-sodium foods are pickles, chicken soup and pretzels.