By Shereen Lehman, MS Updated on July 13, 2020
Medically reviewed by Elena Klimenko, MD
Dietary supplements are products designed to augment your daily intake of nutrients, including vitamins and minerals. Many are safe and offer significant health benefits, but there are some that pose health risks, especially if overused. Dietary supplements include amino acids, fatty acids, enzymes, probiotics, herbals, botanicals, and animal extracts.1
In addition to vitamins and essential minerals, popular supplements include:1
- Fish oil
- Green tea
- St. John’s wort
- Saw palmetto
Normally, you should be able to get all the nutrients you need from a balanced diet. However, supplements can provide you with extra nutrients when your diet is lacking or certain health conditions (such as cancer, diabetes, or chronic diarrhea) trigger a deficiency.
In most cases, a multivitamin/mineral supplement will provide all the micronutrients your body needs. They are generally safe because they contain only small amounts of each nutrient (as measured by the daily value, or DV).
Individual nutrients are available as supplements, usually in doses larger than your typical multivitamin. They can be used to treat a deficiency, such as an iron deficiency, or reduce the risk of a medical condition, such as hypertension.2
For example, large doses of vitamin B3 (niacin) can help raise “good” high-density lipoprotein (HDL) cholesterol,3 while folic acid has long been used to reduce the risk of a birth defect called spina bifida.4 Antioxidants, such as vitamin C and vitamin E, may reduce the toxic effect of chemotherapy drugs (allowing patients to tolerate larger doses of chemo).5
Unless a specific deficiency is identified, a supplement is usually not necessary if you eat and exercise properly. The appropriate use of supplements can help you avoid side effects and toxicities associated with overuse.
In the United States, dietary supplements are not regulated as strictly as pharmaceutical drugs. Manufacturers do not have to prove that they are either safe or effective. The U.S. Food and Drug Administration (FDA) doesn’t even determine whether dietary supplements are effective before they are shipped to market shelves.1
The FDA does maintain a list of tainted or potentially harmful products marketed as dietary supplements. The worst offenders are usually weight loss aids, “natural” sexual enhancement pills, and supplements targeted at bodybuilders.6
Supplement manufacturers have to follow certain labeling guidelines, including what they can say and not about the purported benefits. That doesn’t stop manufacturers from claiming, often misleadingly, that their product can “boost the immune system”7 or “treat arthritis” even if there is little scientific evidence to support the claims. Generally speaking, the FDA only acts on the most serious infractions.
While most dietary supplements are safe as long as you follow the product instructions, large doses of certain nutrients can have adverse effects. You can even overdose on certain supplements, risking serious harm and death.8 Among some the harmful interactions or dosing concerns:
- Vitamin K can reduce the effectiveness of blood thinners like Coumadin (warfarin).9
- Vitamin E can increase the action of blood thinners, leading to easy bruising and nosebleeds.
- St. John’s wort can accelerate the breakdown of many drugs, including antidepressants and birth control pills, thereby reducing their effectiveness.
- Vitamin B6 (pyridoxine), when used for a year or more at high doses, can cause severe nerve damage. Vitamin B6 can also reduce the effectiveness of the anti-seizure drug Dilantin (phenytoin) and levodopa (used to treat Parkinson’s disease).
- Vitamin A used with retinoid acne medications such as Accutane (isotretinoin) and Soriatane (acitretin) can causes vitamin A toxicity.9
- Iron and calcium supplements can reduce the effectiveness of antibiotics, namely tetracyclines and fluoroquinolones, by as much as 40%.
- Vitamin C can cause diarrhea when taken in doses higher than the gut can absorb (but some patients can tolerate 5,000mg to 25,000mg per day).
- Selenium, boron, and iron supplements can be toxic if taken in large amounts.
Advise your healthcare provider about any supplements you plan to take as well as any medications you are currently taking, whether they be pharmaceutical, over-the-counter, herbal, traditional, or homeopathic.
For the utmost safety and quality, choose supplements tested and approved by a certifying body such as the U.S. Pharmacopeia (USP). Never use expired supplements.