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). 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 Mineral||Why You Need It||Recommended Dose Per Day (for adults, ages 19-50)||Tolerable Upper Intake Level (UL)||What Happens if You Take Too Many Vitamins||Good Food Sources|
|Vitamin A||Vision, growth, and immune function||900 micrograms (µg) for men , 700 µg for women)||3,000 µg||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, such as unskinned sweet potatoes|
|Vitamin B6||Protein metabolism, neurotransmitter formation, red blood cell function, and hormone function||1.3 milligrams (mg)||100 mg||If 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 acids||400 µg||1,000 µg||High 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|
|Niacin||Necessary for energy metabolism||16 mg for men, 14 mg for women||35 mg||In 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 C||It is required for the synthesis of collagen and the neurotransmitter norepinephrine||90 mg for men, 75 mg for women||2,000 mg||Generally safe, but at high doses can cause diarrhea and might increase risk of urinary tract stones.||Citrus fruits|
|Vitamin D||It helps to form and maintain strong bones, plus is needed to maintain blood levels of calcium and phosphorus||15 µg||100 µg||Continuous 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|
|Iron||An essential component of hundreds of proteins involved in the transport and storage of oxygen||8 mg for men, 18 mg for women||45 mg||Can 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)|
|Selenium||Necessary for the function of numerous enzymes||55 µg||400 µg||Toxic 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. Also, many supplements may interact with medications you currently take. 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.
Last reviewed April 2014 by Michael Woods, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.