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You take your vitamin and mineral supplements to improve your health, but are you sure they’re not making you ill?

For a variety of reasons, including a few that are quite surprising, it turns out that the supplements you take to achieve optimal health may be harmful. This caution applies not only to individual supplements, but even to the ingredients in multivitamins.

As a reader of Daily Health News, you are quite likely already savvy to some of these dangers, but not all, I’d wager. So I recruited Leo Galland, MD, internist and creator of Pill Advised (http://PillAdvised.com), an online resource for information and interactions involving medications, supplements and food, to tell us about the risks and benefits of the most commonly used vitamins and minerals so you can be confident that what you’re taking will help you feel good, not bad. Today we’re discussing popular mineral supplements -- we’ll cover vitamins in another story next week.

WHAT ARE YOU TAKING?

While most people believe that the only potential harm with vitamins and minerals is with megadoses, that’s not true, Dr. Galland stressed, adding that "research has indicated that adhering to that belief may cost people their lives."

Calcium. You’ve been hearing lots about this mineral in the news lately. While it may help prevent colon cancer and improve bone health, it may also increase the risk for heart attack or prostate cancer. This danger is due to the way calcium interacts with vitamin D. If your calcium consumption is high but your vitamin D level is low, calcium can render the vitamin D in your body less active. That, in turn, increases heart and cancer risk. Meanwhile, the lack of vitamin D also means that your bones, heart and other tissues absorb less calcium, which increases the risk for heart attack and kidney stones.

The research: An analysis of 11 studies published in the July 2010 issue of BMJfound that women taking high doses of calcium (averaging 1,000 mg a day) without vitamin D, and also getting about 800 mg/day of dietary calcium in their diets, had an increased risk for heart attacks. Another study, the Harvard Health Professionals Follow-Up Study, involving 48,000 men with no history of cancer (other than nonmelanoma skin cancer), found that high calcium intake from supplements or food was associated with an increased risk for highly invasive prostate cancer.

Dr. Galland’s advice: Most people should limit calcium supplementation to 500 mg a day, to be taken with 1,000 IU of vitamin D after dinner. He advises aiming to get another 500 mg daily from food (for instance, one ounce of cheddar cheese has 204 mg of calcium) but adds that if you have a history of kidney stones, speak first to your doctor regarding how much calcium in any form you should consume.

Selenium. This powerful antioxidant may decrease the risk for heart attacks and cancers of the stomach, lung, colon and prostate... but don’t take it if you’ve had skin cancer or are at especially high risk for it due to personal or family history.

The danger: Some studies have found that selenium supplements increase the risk for skin cancer, while others suggest an elevated risk for type 2 diabetes.

Dr. Galland’s advice: If you are not at high risk for skin cancer but are at risk for prostate, colon or breast cancer, take 50 micrograms (mcg) to 200 mcg of selenium a day.

Magnesium. Magnesium has a calming effect on the nervous system and helps with stress-related conditions. It also boosts calcium absorption. Magnesium supplements have many benefits, with studies showing that they may prevent some of the complications of diabetes, improve breathing and airflow in adults with asthma, and reduce blood pressure in people with hypertension.

Potential problems: In some people, magnesium has a laxative effect and can cause diarrhea. This is a particular danger for people with digestive disorders such as IBS or Crohn’s disease. What’s more, if your kidneys aren’t working well enough to excrete the magnesium your body doesn’t need, high blood levels can develop, leading to slowed heart rate, reduced blood pressure, slowed breathing and even coma and death.

Dr. Galland’s advice: Twenty-six million Americans have chronic kidney disease and millions more are at increased risk, so do not take magnesium supplements unless you have first had a serum creatinine blood test (typically done during a normal physical), which indicates how well your kidneys are functioning. If your blood tests show that you would benefit from magnesium supplementation or your doctor advises it to address particular symptoms such as muscle spasms or tension, palpitations, difficulty falling asleep or anxiety, Dr. Galland says to start slowly, with 100 mg a day, and then work up to 400 mg/day if needed -- but stop if you find that the supplements cause diarrhea.

Zinc. A zinc deficiency can affect immune function, tissue repair and brain function. According to Dr. Galland, people who have problems resisting infection or whose cuts and wounds heal too slowly could have a zinc deficiency. Zinc is also known to improve mood and helps antidepressant medications work better. Zinc can be particularly helpful for elderly people -- or for anyone -- who will be undergoing surgery.

Caution: Zinc in excess of 40 mg/day may cause a deficiency of copper, which can cause unusual anemia and neurological problems. Zinc can also cause nausea in some people.

Dr. Galland’s advice: Take zinc (15 mg to 40 mg/day) only if your doctor prescribes it based on a blood test.

Copper. This mineral is taken primarily in multimineral supplements but sometimes on its own by people taking zinc supplements (to prevent a copper deficiency).

The dangers: Copper can be very toxic, especially to the nervous system. High levels can cause neurological effects such as insomnia, depression, anxiety or liver or kidney damage, and some experts believe high levels may increase the risk for Alzheimer’s disease. Because copper spurs the growth of new blood vessels, it’s not recommended for anyone with cancer.

Dr. Galland’s advice: Sources for dietary copper include chocolate, nuts, seafood, mushrooms and legumes. The usual dose for those who need supplemental copper is 0.5 mg a day, but people with low blood levels of copper (unusual but sometimes the case in patients with chronic disease) may need much more, 2 mg to 4 mg/day. If you take a copper supplement, it is important to have your serum copper level checked annually, as copper is absorbed more rapidly from a supplement than from food.

Iron. Iron deficiency can cause anemia, fatigue and impaired cognitive function, so iron supplements have been standard fare for those who need them for many years.

Problems: Iron supplements are potentially toxic. Since the body eliminates iron slowly (except in bleeding episodes), it can accumulate in the liver, where it can cause cirrhosis... in the heart, causing heart failure...or in the pancreas, causing diabetes. When iron levels are too high, the toxicity can also generate free radicals that can contribute to cancer risk.

Dr. Galland’s advice: Most adult men and postmenopausal women don’t need iron supplements -- they should be taken only if the level of blood ferritin is found to be low, and then only long enough to bring it up to the desired level. Dr. Galland notes that this is true even among premenopausal women. The usual dose for those who need iron is 20 mg to 30 mg a day.

READ LABELS AND GET RID OF WHAT YOU DON’T NEED

In summary, Dr. Galland says that mineral supplements aren’t for everyone. In fact, he said, "a lot of people shouldn’t be taking them individually," adding that for a few vulnerable individuals even the amounts found in typical multivitamins can prove dangerous. He stressed that mineral supplementation must be tailored to individual needs, emphasizing the importance of taking minerals only under the supervision of a doctor trained in their use.

And one final tip: Noting that many people take supplements that are in combination pills or capsules, Dr. Galland pointed out that it’s possible you aren’t even aware of what minerals you are taking. He urges readers to look closely at the label of any supplements they take to be sure they’re getting only what they need and aren’t ingesting anything that could prove harmful. Look for our important update on vitamins next week.