Our bodies store some minerals in large amounts. Sodium, chloride, and potassium help maintain a proper balance of water. Calcium, phosphorus, and magnesium support bone health. Sulfur helps stabilize protein structures, including those in hair, skin and nails.
Having too much of one major mineral can result in a deficiency of another. For example, if we ingest too much sodium through table salt or processed foods, we could end up losing needed calcium. Likewise, too much phosphorus can afftect magnesium absorbtion.
These imbalances are usually caused by overloads from supplements, not food sources.
The major minerals calcium and phosphorus each account for more than a pound of our body weight. On the other hand, all the trace minerals in our bodies -- if distilled -- would only fill a thimble. But they are just as important. For example:
- Iron ferries oxygen throughout our bodies.
- Fluoride strengthens bones and prevents tooth decay.
- Zinc helps blood clot, is essential for taste and smell, and bolsters the immune response.
- Copper helps with iron metabolism and the creation of hemoglobin, which carries oxygen in the blood.
Insufficient amounts also cause problems. Too little iodine slows hormone production, causing sluggishness and weight gain. It's a delicate balance; the margin between too much and too little is small.
Food is usually a safe trace mineral source. But supplements can create unsafe excesses.
Here's a quick overview of current wisdom on several minerals in supplements:
Calcium: The Institute of Medicine (IOM) suggests:
- From age 19 to 50, aim for 1,000mg a day.
- After age 50, only women should aim a little higher -- to 1,200mg.
Iron: With a few exceptions, most of us don't need supplemental iron. Instead, we risk iron overload. The large Framingham study suggested that the low risk of heart disease among premenopausal women could be a result of monthly iron loss through menstruation. This observation suggests that the increased rate of heart disease in postmenopausal women could result from increasing iron accumulation. Men don't need extra iron unless they have a condition with chronic blood loss. There are no benefits -- only risks -- from taking iron supplements. If you take a mutivitamin or mineral pill, look for one without iron.
Potassium: Most Americans get barely half of the recommended amount of potassium in their diets. Potassium-rich diets have a beneficial effect on blood pressure and are associated with a lowered stroke risk. So should you take a potassium supplement? In spite of some positive commentary about cardiac health, the common wisdom is -- get potassium from food, not pills. Baked potatoes -- sweet or white -- head the list of potassium-rich foods. Bananas, too.
Selenium: This trace mineral has been touted for preventing cancer -- particularly prostate cancer -- and for helping other conditions, like asthma, heart disease, rheumatoid arthritis, even male infertility. Contrary to some earlier small, promising studies, the large "Selenium and Vitamin E Cancer Prevention Trial" found no benefit against prostate cancer from either supplement. Moreover, people taking selenium had a slightly increased risk of diabetes. A later 2009 study found that higher selenium levels might actually make prostate cancer worse. Now they tell me! I've had prostate cancer since at least the mid-1990s, and -- thanks to the early hype for selenium -- I took the supplement for a couple of years. Bottom line: I should get this mineral from selenium-rich foods, like whole grains and nuts (particularly Brazil nuts). But avoid the supplement!
Zinc: Most Americans get the RDA from their diets, since this trace mineral is found in seafood, meat, poultry, dairy products and nuts. You've probably seen the ads touting zinc lozenges to snuff out the common cold. The results of 14 double-blind, placebo-controlled trials conducted over the past 25 years ended up a draw: half showed the lozenges shortened the duration of a cold; half showed no effect. If you take zinc lozenges for cold relief, read the label to be sure you're not exceeding the RDA (11mg for men, 8mg for women). And remember that most daily multivitamins contain the RDA for zinc. Levels not much higher than 15mg can trigger side effects, like depressed immune system, poor healing, hair loss, and decreased sense of taste and smell. Many experts recommend we get zinc from food, not pills. Seeing a pattern?
Sources: Much of the information here comes from two excellent reports: The Truth about Vitamins and Minerals, published by the Harvard Medical School, and Dietary Supplements, a "Wellness Report" from the University of California--Berkeley, School of Public Health.