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The 10 Vitamins & Other Nutrients That can be HARMFUL When Taken in Excess

An estimated 150 million Americans take dietary supplements on a daily basis in an effort to add nutrition to their diets. In 2006 alone, nearly 94 million multivitamin supplements were sold (not including those sold by Wal-Mart), according to Information Resources, Inc., along with:

  • 63 million individual "letter" vitamins

  • 57 million non-herbal supplements

  • 51 million mineral supplements

  • 29 million herbal supplements

dietary supplements

Do you have a cabinet full of dietary supplements? Be sure you're not getting too much of a good thing by monitoring the amount of vitamins you're taking.

However, be wary of the mindset that if a little is good, more is even better. While it's nearly impossible to overdose on vitamins from eating whole foods, it is possible to get excessive, potentially harmful amounts of nutrients when taking them in supplement form.

This is particularly true of fat-soluble vitamins, which accumulate in your body and are stored for later use (water-soluble vitamins, meanwhile, are not readily stored in the body), though even water-soluble vitamins and minerals can be problematic in large doses.

The Best Way to Get Your Vitamins

Of course, the best way to get the nutrients your body needs is by eating a variety of healthy foods (or in the case of vitamin D, getting it through safe and sensible sun exposure). Whole foods contain an array of health-promoting micronutrients and phytochemicals that provide a beneficial synergistic effect that is not obtained when you take isolated vitamin supplements.

That said, there is a wide disparity in quality among supplements on the market, and if you do choose to take them you should do your homework to find a reputable manufacturer of high-quality natural supplements.

Meanwhile, some physicians in the natural health field do recommend high doses (beyond the typical government limits) of certain nutrients, such as vitamin C, for the treatment of specific health conditions.

Vitamins to Keep a Close Watch On

If you take any of the following dietary supplements, particularly in mega-dose form, or if you take a variety of multivitamins everyday, be careful that you are not exceeding a healthy amount. The Daily Recommended Dietary Allowances and Tolerable Upper Intake Levels listed below are provided only as a guide. Taking supplements in excess of or below these amounts should only be done under the guidance of a knowledgeable health care professional.

1. Iron

Taking too much iron can lead to liver problems, accumulation of fluid in the lungs, fatigue, headache, low blood sugar, coma and testicular problems in men.

Daily Recommended Dietary Allowance (RDA): 8 mg for men, 18 mg for women (8 mg for women 51 and over)

Tolerable Upper Intake Levels (UL) (This is the highest dose adults can take without experiencing adverse effects): 45 mg/day

2. Vitamin A

Excess vitamin A (even at just double the RDA) can increase the risk of birth defects and cause liver damage, reduced bone mineral density (which can lead to osteoporosis), and central nervous system disorders.

RDA: 3,000 IU (International Units) for men, 2,310 IU for women

UL: 10,000 IU/day

3. Vitamin C

Taking large amounts of vitamin C can lead to gastrointestinal upset and diarrhea. There are also reports (that have yet to be confirmed) that it may cause genetic mutations, birth defects, increased oxidative stress, kidney stones and even cancer.

RDA: 90 mg for men, 75 mg for women

UL: 2,000 mg/day

4. Calcium

Though rare, excessively high intakes of calcium can lead to hypercalcemia (elevated levels of calcium in the blood), impaired kidney function and decreased absorption of other minerals, including iron, zinc, magnesium, and phosphorus.

dietary supplements

Before taking any dietary supplement, be sure to talk with your doctor. Many of them contain active ingredients that can interact with medications, foods and each other, causing some unwanted (and unexpected) effects.

RDA: 1,000 mg for adults 19-50, 1,200 mg for those 51 and over

UL: 2500 mg/day

5. Vitamin E

Because vitamin E is an anticoagulant, taking too much may increase the risk of bleeding problems. Also, according to the American Heart Association, excess amounts (even 400 IU/day or more) of this vitamin may increase the risk of death.

RDA: 22.5 IU

UL: 1,500 IU/day

6. Vitamin D

When taken in excess, vitamin D can raise blood levels of calcium, which can cause mental changes, such as confusion. It can also result in nausea, vomiting, poor appetite, constipation, weakness, and weight loss.

Adequate Daily Intake (AI) (used when there is not enough scientific evidence available to establish an RDA): 400 IU, 600 IU for those 71 and over

UL: 2,000 IU/day

7. Zinc

A zinc overdose (which can occur from as little as150 to 450 mg/day) can reduce immune function and good cholesterol levels, and alter iron function and copper levels.

RDA: 11 mg for men, 8 mg for women

UL: 40 mg

8. Selenium

In rare instances, too much selenium can result in a condition called selenosis (this occurs when selenium blood levels are greater than 100 µg/dL). Symptoms of selenosis include gastrointestinal upset, hair loss, white blotchy nails, garlic breath odor, fatigue, irritability, and mild nerve damage.

RDA: 55 µg

UL: 400 µg/day

9. Vitamin B6

At high doses (lower than 500 mg per day), vitamin B6 can result in nerve damage to the arms and legs.

RDA: 1.3 mg for those 19-50, 1.7 mg for men 51 and over, 1.5 mg for women 51 and over

UL: 100 mg/day

10. Copper

Taking too much copper can lead to organ damage (liver and kidneys) and neurologic problems. Other symptoms include weakness, abdominal pain, nausea, learning disabilities, memory lapses, diminished concentration, insomnia, seizure, delirium, stuttering and hyperactivity.

RDA: 900 mcg

UL: 10,000 mcg

Recommended Reading

The Seven Nutrients Americans are Most Deficient In & How to Get Them

Do You Really Need a Multivitamin Supplement?

USDA Food and Nutrition Information Center

Linus Pauling Institute at Oregon State University

Medline Plus: Drugs & Supplements

The Seattle Times February 28, 2007

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