Image for HCA vitamins article Around 400 BC, the celebrated Greek physician Hippocrates offered some advice about diet and health. He declared, "Let food be thy medicine and medicine be thy food." The growing number of Americans who turn to supplements to make up for a poor diet ought to pay attention to those words of wisdom.

Each day, millions of adults in the United States take high doses of vitamins and minerals with hopes of feeling better, getting sick less often, and living longer. For years, physicians told consumers that, at worst, they were just wasting their money. But now, the word is to be careful—because high doses of certain vitamins and minerals may actually increase the risk of disease.

Dietary Supplements 101

As you probably already know, we need vitamins—by far the most popular choice of supplement—to live (that is, they are ‘vital’ to our survival). But the body cannot make them on its own, so we must get vitamins from our diet. Similarly, we need minerals like iron and calcium to function, and must rely on outside sources to meet our requirements. (Other supplements, such as herbs, are a whole other story.)

Although supplements are a good idea in certain cases (such as for pregnant women, the elderly, and vegetarians), experts agree the best way for you to get the nutrients you need is by eating a well-balanced, healthful diet.

Too Much of a Good Thing

One hundred years ago, scientists began to identify the nutrients in foods that we need to avoid getting deficiency diseases like beriberi and rickets. With attention being given to the benefits of vitamins and minerals, it’s no wonder that many of us choose to take supplements. Problems arise, however, when people take individual vitamins or minerals in excessive amounts, rather than eat a nutritious diet.

Use the following chart as a guide:

Supplements: Recommended Intake Levels of Some Supplements and Known Risks Associated With Excessive Amounts
Vitamin or MineralWhy You Need ItRecommended Dose (for adults, ages 19-50)Tolerable Upper Intake Level (UL)What Happens if You Overdo ItGood Food Sources
Vitamin AVision, growth, and immune function900 micrograms per day (µg/d) for men (equivalent to 2,997 International Units), 700 µg/d for women (2,333 IU/d)3,000 µg/d (10,000 IU/d)Too much may cause hair loss, nausea, and vomiting, and may increase the risk of bone fracture. Very high intakes can cause liver disease and fetal malformations.Preformed vitamin A sources include fortified cereal, eggs, and dairy products; Provitamin A carotenoids (like beta-carotene), found in deep orange and dark green fruits and vegetables
Vitamin B6Protein metabolism, neurotransmitter formation, red blood cell function, and hormone function1.3 milligrams per day (mg/d)100 mg/dIf taken at very high doses, may result in painful neurologic symptoms and difficulty walking.Fortified cereals, beans, meat, poultry, fish, and some fruits and vegetables
Folic acid (folate)DNA metabolism as well as the metabolism of several important amino acids400 µg/d1,000 µg/dHigh doses, while safe in themselves, may mask symptoms of, the rare disease, pernicious anemia allowing it to progress unchecked.Fruits and vegetables, fortified grain foods
NiacinNecessary for energy metabolism16 mg/d for men, 14 mg/d for women35 mg/dIn doses fifty times higher than the tolerable upper intake level, can damage the liver and cause severe gastrointestinal problems.Meat, poultry, fish, fortified cereals, legumes, milk, and seeds
Vitamin CIt is required for the synthesis of collagen and the neurotransmitter norepinephrine90 mg/d for men, 75 mg/d for women2,000 mg/dGenerally safe, but at high doses can cause diarrhea and might increase risk of urinary tract stones.Citrus fruits
Vitamin DIt helps to form and maintain strong bones, plus is needed to maintain blood levels of calcium and phosphorus15 µg/d100 µg/dContinuous very high intakes might lead to damage to the heart, blood vessels and kidneys due to calcification.Fatty fish (herring, salmon, sardines), eggs from hens that have been fed vitamin D, and fortified milk; exposure to sunlight provides another important source
IronAn essential component of hundreds of proteins involved in the transport and storage of oxygen8 mg/d for men, 18 mg/d for women45 mg/dCan poison a child, causing nausea, vomiting, lethargy, fever, difficulty breathing, coma, and even death; in adults excess iron is theorized to increase risk of heart disease.Lean red meats, shellfish, legumes, dried fruit, and green leafy vegetables (Note: iron from non-meat sources is best absorbed when vitamin C is also present)
SeleniumNecessary for the function of numerous enzymes55 µg/d400 µg/dToxic effects of overdosage include hair and nail brittleness and loss, gastrointestinal disturbances, skin rashes, fatigue, irritability, and nervous system abnormalities.Organ meats, seafood, and grains
The Bottom Line

While it may be promising, the evidence so far linking supplements with a reduced risk of chronic disease is much less convincing than most people realize. What is clear is just how easy it is to overdose on certain supplements. Therefore, your best bet is to get most of the nutrients you need from the foods you eat. For a healthful diet, be sure to include lots of fruits and vegetables, whole grains (like whole wheat bread and brown rice), unsaturated fats (found in nuts, avocados, and oils), and low-fat dairy products.

If you do take supplements, keep the following in mind:

  • A multivitamin cannot provide adequate calcium, and for this reason many people could benefit from a separate calcium supplement.
  • Be wary of unfounded medical claims for dietary supplements.
  • Talk to your doctor about all supplements you take, including concentrations and amounts.
  • Keep supplements out of the reach of children.