Dietary supplements are pills, capsules, tablets or liquids containing nutrients. They can contain, for instance, (multi)vitamins, minerals or fish oils. As their name suggests, dietary supplements are intended to supplement the diet. People may take supplements when their diet does not provide all the nutrients they need. Dietary supplements are not drugs. They are not intended to treat, prevent or cure diseases.
Dietary supplements: the basics
Have you ever taken a dietary supplement, such as (multi)vitamins or fish oil? Dietary supplements are very easy to get by. You can buy them at the grocery store, drug store or convenience store. And there are lots of them! Multivitamins, fatty acids, single nutrients, fibers, minerals, antioxidants… one can easily get lost. Therefore, we will look at some basic facts and figures about dietary supplements.
What are dietary supplements?
Dietary supplements, or food supplements, are pills, capsules, tablets or liquids containing nutrients. They can contain, for instance, (multi)vitamins, minerals or fish oils. As their name suggests, dietary supplements are intended to supplement the diet. People may take supplements when their diet does not provide all the nutrients they need. Dietary supplements are not drugs. They are not intended to treat, prevent or cure diseases. In fact, in the United States, claiming that dietary supplements prevent or treat any disease is against the federal law . Note that food supplements are different from food additives. Food additives are chemicals that alter the flavor, color or longevity of food.
What are the ingredients in dietary supplements?
The key ingredient of dietary supplements are nutrients. Nutrients can be a) extracted from food sources, or b) synthetically manufactured, or c) both. In the first scenario, nutrients can be derived from animals such as chicken or fish, or from plants such as algae or soybeans. Synthetically manufactured nutrients are produced by humans, for instance in a factory. Some nutrients in dietary supplements are essential to a healthy life (e.g., certain vitamins). Others contain substances that have not been confirmed as being essential to life, but are marketed as having beneficial health effects (e.g., plant pigments or polyphenols). Finally, dietary supplements can also contain so-called excipients, such as starch or cellulose to keep everything together, food colorants, flavours and preservatives.
Do I need to take dietary supplements?
Dietary supplements are intended to help people consume all the nutrients they need for a healthy life. In principle, these nutrients can be derived from a healthy diet. Many countries and health organisations have published dietary guidelines (for example, have a look at the 2015-2020 Dietary Guidelines for Americans published by the US Ministry of Health ). People who are generally healthy and adhere to a healthy diet, will derive all the nutrients they need from their diet. They do not need dietary supplements.
Yet, dietary supplements may be necessary in two situations. First, a doctor may advise you to take dietary supplements if you are not generally healthy or if you belong to a so-called at-risk group. For instance, pregnant women, newborns and patients with metabolic disorders may benefit from specific dietary supplements. Second, dietary supplements may be useful when your diet does not provide all the nutrients you need. This may be the case when you choose to adhere to, for instance, a vegan diet.
Note: if you experience symptoms of nutritional deficiencies despite adhering to a healthy diet, it is always advisable to consult a doctor or nutritionist. You might unknowingly belong to an at-risk group for whom dietary supplements are recommended.
Why do so many people take dietary supplements?
A recent study showed that approximately 50% of people in the US take dietary supplements at least once per month . More than three quarters of all supplements in the US are bought without recommendation of a healthcare provider . Interestingly, the people who take dietary supplements seem to be the ones who need them the least: those who use dietary supplements (compared to non-users) are – on average – more physically active, less likely to smoke or drink heavily, and are less often underweight or obese .
The most widely-used type of dietary supplement in the US is multivitamin-minerals (32%), followed by calcium-containing supplements (12%) and omega-3 fatty acids and fish oils (10%). Most people report taking dietary supplements to improve or maintain overall health. Others hope to improve bone health, or get more energy. A small proportion of dietary supplement users (4%) report using supplements to improve their mental health. 
 Dietary Supplement Health and Education Act of 1994, retrieved from https://ods.od.nih.gov/About/DSHEA_Wording.aspx#sec5 on 9 December 2019
 2015-2020 Dietary Guidelines for Americans. Office of Disease Prevention and Health Promotion. Retrieved from https://health.gov/dietaryguidelines/2015/ on 9 December 2019
 Kantor ED, Rehm CD, Du M, White E and Giovannucci EL (2016). Trends in Dietary Supplement Use Among US Adults From 1999-2012. JAMA 316 (14), 1464-1474
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 Gahche JJ, Bailey RL, Potischman N, Ershow AG, Herrick KA, Ahluwalia N, Dwyer JT. (2018). Federal Monitoring of Dietary Supplement Use in the Resident, Civilian, Noninstitutionalized US Population: National Health and Nutrition Examination Survey. The Journal of Nutrition, 148(suppl 2) 1436S–1444S