The Hidden Dangers of Dietary Supplements

By Pieter Cohen, MD, Cambridge Health Alliance, Harvard Medical School. On Tuesday, April 27, 2010, Dr. Cohen joined Dr. Oz to discuss the hidden dangers of herbal supplements and provided tips on choosing and using them safely.

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Dietary supplements encompass a wide range of products that includes vitamins and minerals, herbal products, amino acids, tissue extracts and other compounds.  Many dietary supplements - which I'll refer to as supplements - are extremely helpful in preventing illness; for example, folic acid can prevent birth defects, and calcium and vitamin D can prevent fractures. 

However, not all supplements are effective.  There are tens of thousands of supplements sold in the US, and while some are very effective, many are not.  Even worse, some might actually cause more harm than good.  Little is known about the safety of supplements, because Congress requires that the US Food and Drug Administration (FDA) assume that all supplements are harmless until proven otherwise.  Because the government does not ensure supplement safety, it's especially important that consumers are careful when purchasing supplements. 

Here, I'll summarize some of the most important safety concerns with supplements and then provide advice for selecting supplements safely.

Manufacturers of supplements do not need to prove that their supplement is effective before selling it. Since there is no required testing of supplements before they are sold, the consumer should keep in mind that information provided on the bottle, brochures or websites are only manufactures' advertising claims.  These statements are not approved by the FDA and the manufacturer can make a claim on the label without providing the FDA (or consumers) with any evidence that it is accurate.

Manufacturers of supplements do not need to inform consumers about side effects even when the ingredients are known to cause side effects. Any ingredient in supplements that has a positive effect on the body also has the potential to have negative effects.  But even when it is established that an ingredient in a supplement causes side effects, the manufacturer does not need to inform the consumer.  For example, bitter orange - a common herbal ingredient in weight loss supplements - causes high blood pressure and racing heart rate.  But when bitter orange is sold, there is no requirement that consumers are informed about these side effects. 

The same is true with medication interactions. Certain supplements, such as St John's wort, can have serious interactions with prescription medications, but there is no requirement that manufacturers provide this information to the consumer.

Little is known about the health effects of combination herbal supplements. Each herbal ingredient may have its own positive and negative effects on the body. When many different herbal ingredients are in the same supplement, the effect on the body is usually not understood - even by experts.  For a consumer it might be impossible - even after carefully researching the ingredients - to determine what effect a multiple ingredient herbal supplement has on one's health.

The amount of ingredients listed on labels is often inaccurate. Many supplements contain different amounts of ingredients than what is listed on the label.  Studies have found that poor quality supplements are sold both at retail stores as well as over the Internet.  Some experts estimate that 1 in 4 supplements sold have labeled quantities that are inaccurate.  Usually there is too little of an ingredient, but sometimes there is too much.  Recently, over 100 people became ill when a multivitamin contained 200 times the labeled amount of selenium.

Contaminants have been found in many supplements, especially those sold over the Internet.  Supplements have been found to be contaminated with pesticides, heavy metals, prescription medications as well as entirely new chemicals.  All of these types of contaminants can cause serious health effects.  Some "herbal" weight-loss pills have been found to contain a cocktail of potent medications including amphetamines, tranquilizers and antidepressants.  Contaminated pills have caused kidney failure, liver failure, heart attacks and dependence.  Physicians are particularly concerned by supplements contaminated by entirely new chemicals or analogs.  Analogs are similar to prescription medications but with slight chemical changes made to their structure.  These analogs are often added so that the chemical cannot be detected by the FDA.  However, even slight changes to the chemical structure of a medication can cause life-threatening side effects. 

Here are 8 tips for safe use of supplements:

  1. The best way to use supplements safely is to avoid supplements you don't need. Use supplements only if you have reliable information that the ingredient(s) will benefit you. Accurate information can be found at the National Institute of Health's National Center for Complementary and Alternative Medicine.  
  2. Select supplements with only the ingredient(s) that you need. If you need vitamin D then select a supplement that only contains vitamin D.
  3. Avoid supplements with more than one herbal ingredient. It is very difficult to determine the effect that multiple herbs will have on your health.
  4. If you take prescription medications or have health conditions, ask your physician if the supplement you are considering is safe for you.
  5. Avoid supplements that are sold to treat an illness, for example supplements sold to treat diabetes, high blood pressure, or high cholesterol. These supplements are more likely to be contaminated with prescription medications.
  6. Avoid supplements that claim to help you lose weight or improve sexual or athletic performance. These supplements may not only be contaminated with prescription medicines but also with dangerous analogs.
  7. Purchase supplements in retail stores rather than over the Internet.
  8. If you experience a side effect from a supplement: Stop using the supplement, inform your physician, and inform the FDA.

By carefully selecting and using supplements, you can obtain the most benefit from supplements while minimizing the chances of serious side effects.

For more information on herbal supplement safety: