What are dietary supplements?

Dietary supplements contain nutrients such as vitamins or minerals that are also found in regular foods, but in a more concentrated form and often at a higher dose. They come in various forms, such as tablets, capsules, powders, liquids, and fizzy, soluble tablets. A is not necessarily made from plants, such as garlic: it could also be an animal product, like fish oil, or synthetic, like most vitamins.

Dietary supplements are over-the-counter products, which means you don't have to go to a pharmacy to buy them. They are also available in places like drug stores and supermarkets. They may also be part of (complementary) medical treatment. German law stipulates that they are not allowed to have (or claim to have) a medicinal effect – for example, lowering blood pressure or blood sugar levels. If a had such an effect it would have to be officially approved as a drug.

Dietary supplements may contain the following substances, for instance:

  • Vitamins, such as vitamin C, vitamin E or
  • Provitamins like
  • Vitamin-like substances (such as coenzyme Q10)
  • Minerals and trace elements (such as , magnesium, iron and zinc)
  • Fatty acids (such as omega-3 and omega-6 fatty acids)
  • Parts of proteins (such as L-cysteine and L-carnitine)
  • Carbohydrates (such as the fiber oligofructose)
  • Other ingredients like brewer's yeast, algae and probiotics

Taking dietary supplements means that the body may absorb much more of these substances than would be possible by just eating a normal diet. In Germany, there are no legal limits on how much of these substances the supplements may contain, but the German Federal Institute for Risk Assessment (BfR) does issue recommendations.

All dietary supplements must be labeled as such, and the labels must provide the following information:

  • Amount and dose of the ingredients
  • Recommended daily dose that should not be exceeded
  • A reminder that dietary supplements cannot replace a balanced diet
  • A warning to keep the supplements out of the reach of children

Who checks the quality and safety of dietary supplements?

According to German law, dietary supplements are regarded as food products, not drugs. Drugs are pharmacologically active substances that have a particular effect on the body and its functions. They are taken to relieve symptoms and illnesses, or for prevention. Dietary supplements do not have a pharmacological effect, and manufacturers aren't allowed to claim that they do – their sole purpose is to provide the body with nutrients. For this reason, they have different quality and safety requirements than chemical or herbal medicines do.

In Germany, the responsibility for the safety of dietary supplements lies with the manufacturers and retailers – as it does with all food products. All dietary supplements must be registered with the German Federal Office of Consumer Protection and Food Safety (BVL). For dietary supplements, the authorities only record which ingredients are listed on the label. But they can take samples of the products to check them.

So dietary supplements don't have to go through all of the strict tests and quality assurance processes that are required of medicines before they are sold on the market. This means that it's not always possible to be sure that all products have the same quality.

When should you be careful?

It's a good idea to be especially careful when ordering products on the internet. Products that are ordered from abroad will not automatically conform to German food safety laws. Because other countries have different regulations, a might contain such a large amount of a substance that it would be considered a drug in Germany. It could also contain substances in quantities exceeding the limits recommended by German regulators.

Because dietary supplements are regulated like food products rather than like medicines, they are not allowed to be advertised as substances that cure, relieve or prevent illnesses, or that are suitable for a specific therapeutic use. That is why dietary supplements are often claimed to have more general effects such as "supports your ," "has a hormone-balancing effect" or "supports the health of your joints." It's important to know that most of these claims are unproven, though, and don't tell us anything about the actual health benefit of taking the product.

Do you need to take dietary supplements to stay healthy?

If you eat a balanced and varied diet, you will get all the nutrients your body needs. So you won't need to take extra vitamins or minerals. In certain cases, it may make sense to take dietary supplements on a temporary basis with the specific aim of correcting a deficiency.

But some dietary supplements have been proven to have no effect on certain illnesses. For example, studies have shown that – contrary to popular belief – taking vitamin C cannot prevent a cold. Vitamin supplements do not help to prevent cancer or cardiovascular (heart and blood vessel) disease either.

Can dietary supplements have harmful effects?

Because manufacturers of dietary supplements don't have to provide that their products are safe, harmful effects can't always be ruled out. There are some dangerous or hazardous substances that dietary supplements aren't allowed to contain. But vitamins and other substances can also be harmful to your health. Some people might have allergic reactions to plant-based ingredients, for example.

Research suggests that products containing vitamin A, vitamin E, or beta-carotene might increase the risk of developing certain diseases might increase the risk of developing certain diseases when taken over a longer period of time and at a high dose. For this reason, the German Federal Institute for Risk Assessment (BfR) requires all manufacturers of vitamin supplements to limit the amounts of e.g. carotenes in their products.

Also, dietary supplements may affect the way medicines work. For this reason, if a doctor prescribes medicine for you, it's important to let them know if you are regularly taking any dietary supplements.

People who are considering taking dietary supplements should ask themselves the following questions first:

  • Why do I want to take this product?
  • Is there scientific research showing that this product will help me to reach that goal?
  • Would there be any disadvantages if I did not take this product?
  • What other ways are there to do something good for my health?

You can find more information at the German Federal Institute for Risk Assessment (BfR).

Bjelakovic G, Nikolova D, Simonetti RG, Gluud C. Antioxidant supplements for preventing gastrointestinal cancers. Cochrane Database Syst Rev 2008; (3): CD004183.

Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev 2012; (3): CD007176.

Bundesinstitut für Risikobewertung (BfR). Health assessment of food supplements.

Bundesinstitut für Risikobewertung (BfR). Assessment of substance risks in food.

EUR-Lex. Guideline 2002/46/EG – Ensuring safe food supplements in the EU. February 03, 2016.

Food and Drug Administration (FDA). What You Need to Know about Dietary Supplements. May 2017

Michaud LB, Karpinski JP, Jones KL, Espirito J. Dietary supplements in patients with cancer: risks and key concepts, part 1. Am J Health Syst Pharm 2007; 64(4): 369-381.

Michaud LB, Karpinski JP, Jones KL, Espirito J. Dietary supplements in patients with cancer: risks and key concepts, part 2. Am J Health Syst Pharm 2007; 64(5): 467-480.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Updated on February 4, 2021
Next planned update: 2024

Authors/Publishers:

Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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