How Dietary Supplements Work

The U.S. market for dietary supplements is over $19 billion. BSIP/UIG/Getty Images

Chances are good there are some dietary supplements right now in your cupboard. Research shows nearly 70 percent of Americans are downing them, helping drive a $19 billion market in 2015. Even more eyebrow-raising, by 2024, the global dietary supplement market size is expected to hit a whopping $278 billion, fueled by the increasing use of supplements to treat malnutrition and cardiovascular disorders [sources: Council for Responsible Nutrition, Globe Newswire].

Dietary supplements are tablets, capsules, powders or liquids that contain vitamins, minerals, herbs, amino acids and/or enzymes. People use them not only to stay healthy, but also to avoid prescription drugs, lose weight, or even to enhance sports or sexual performance. And this is nothing novel.


Humans have been using some form of dietary supplements since the dawn of civilization. Five-thousand-year-old Sumerian clay tablets are inscribed with records of the herbs they used — the earliest known written records. In addition, Asian cultures have a rich history of herbal usage stretching back more than 3,000 years. The book in English on herbs was published in 1526 [source: Herbal Academy].

Today's supplement industry is strong and growing, fueled by recommendations from physicians, friends who swear by one natural remedy or the other, and aggressive marketing by supplement companies themselves. In the U.S., most supplement users take vitamins and minerals, with the humble multivitamin the most popular item, followed by vitamin D, vitamin C and calcium. In the specialty supplement category, Omega 3/fatty acids, fiber and probiotics are the most popular, while among herbals and botanicals, Americans favor green tea, cranberry, garlic and ginseng. Generally, men and women are equally enamored of the products [source: Council for Responsible Nutrition].

But just as with other health-related products or practices, guidance on supplements is constantly changing as science evolves. In 2013, women were flummoxed when the U.S. Preventive Services Task Force said postmenopausal females should not be taking calcium and vitamin D, as neither helped prevent bone fractures. Even worse, some studies linked calcium supplementation with heart disease, kidney stones and gastrointestinal problems.

However, another study by the Women's Health Initiative found long-term use of calcium and vitamin D did appear to substantially lower the risk of hip fractures in postmenopausal women, with little risk for kidney stones. So, who is correct? Today, many doctors tell patients of both sexes to nix the calcium supplements, regardless of age, and instead eat three or four servings of calcium-rich foods daily [sources: Cooper, Ray].

Perhaps as concerning as constantly changing supplement recommendations is the fact that many people today are ingesting an astonishing array of supplements that have no scientific evidence of being effective.


Federal Regulation of Supplements

Supplements are displayed in a shop May 26, 2010, in New York City. A U.S. government probe into herbal and dietary supplements found that some contained contaminants and used false marketing claims. Mario Tama/Getty Images

Perhaps the biggest potential danger regarding supplements — and the most important thing consumers need to realize — is that the industry today is only loosely regulated. It wasn't always this way. Before 1990, dietary supplements were tightly controlled by the Food and Drug Administration (FDA). Too tightly controlled, some say, nearly causing the industry to collapse. Part of the tight control meant "dietary supplements" referred to only a few essential nutrients, including vitamins, minerals and proteins, and after 1990, also herbs. But in 1994, there was a huge change [source: FindLaw].

That year, Congress passed the Dietary Supplement Health and Education Act (DSHEA), which expanded the definition of "dietary supplement" to include amino acids (e.g., lysine, tryptophan), and metabolites and extracts (e.g., bilberry extract, chamomile tea), among other substances. It also defined dietary supplements as food, not as drugs or food additives (like spices). These changes meant supplements suddenly had much less federal oversight or regulation, and the industry boomed [sources: FindLaw, Scarbrough, Institute of Food Technologists].


In exchange for the looser regulation, makers of dietary supplements could not claim their products cured any diseases (because that would make them drugs regulated by the FDA). They also had to include all ingredients on a product's label, and identify that the product was a "dietary supplement." Although a label could make a claim about the supplement's positive effect on the body, it also had to say, "This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease." It was up to the manufacturer to ensure that its product was safe, although the secretary of Human and Health Services could declare that a supplement or an ingredient in a supplement was hazardous to health [source: FindLaw].

The FDA has established good manufacturing practices for supplement producers to help ensure you're getting what's advertised — that your capsules don't contain too much or too little of an ingredient, for example, or a contaminated product. And the FDA occasionally will inspect a supplement manufacturing facility. But the FDA does not have to approve a supplement before it can be brought to market [source: National Institutes of Health].

To help ensure supplements are safe, several independent organizations offer quality testing. If a manufacturer submits a supplement to the testing and passes, the product is allowed to carry a seal of approval that guarantees it was properly manufactured, contains the ingredients on its label and doesn't have harmful levels of contaminants. Some of the more notable testing organizations are, NSF International and U.S. Pharmacopeia. A few of the hundreds of supplements that earned quality seals are supplements produced by Kirkland (Costco), NatureMade and Nutrilite (Amway) [sources: National Institutes of Health, Quality Supplements, NSF].

However, even a quality seal doesn't mean any given supplement will work for you, or that it's safe for your body. And that is one of the ongoing debates.


Wise Supplement Usage

Probably the most frequent questions regarding supplement usage are which supplements to use and which to avoid. The answer to the first question depends on your body and its unique needs, so always consult your physician before using any supplement. That being said, Consumer Reports and the Natural Medicines Comprehensive Database, an independent research group, compiled a list of some of the top supplements that research shows are likely safe and may be effective for certain conditions. These are:

  • Calcium
  • Cranberry
  • Fish oil
  • Glucosamine sulfate
  • Lactase
  • Lactobacillus
  • Psyllium
  • Pygeum
  • SAMe
  • St. John's wort
  • Vitamin D

The two groups also identified a dozen supplement ingredients to be avoided due to their links to serious side effects:


  • Aconite
  • Bitter orange
  • Chaparral
  • Colloidal silver
  • Coltsfoot
  • Comfrey
  • Country mallow
  • Germanium
  • Greater celadine
  • Kava
  • Lobelia
  • Yohimbe

For example, coltsfoot — thought to be effective for bronchitis and asthma — is linked to liver damage and cancer. Bitter orange, supposedly useful for weight loss, nasal congestion and allergies, may cause fainting, heart attack, stroke and even death [source: Consumer Reports].

While it's handy to have "good" and "bad" lists, don't rush off to the store and purchase all 11 of the "good" supplements listed above. Your body might not need them, for one. Also, some of the evidence as to whether these supplements "work" is conflicting. For instance, some studies say glucosamine sulfate helps relieve pain and improves joint function for people with arthritis. Other studies say it only relieves joint pain [source: Arthritis Foundation].

Finally, not all supplements are of the same quality. Become a savvy supplement shopper by following these practices [source: U.S. Food & Drug Administration]:

  • If you're looking online for supplement information, use noncommercial sites such as the National Institutes of Health (NIH), U.S. Food & Drug Administration (FDA) and the U.S. Department of Agriculture (USDA).
  • Be wary of any product that says "totally safe," "has no side effects" or "works better than [prescription drug name]."
  • Keep in mind no supplement should claim to be able to prevent, treat or cure a disease. It's against the law for companies to do that because the supplement then would be considered a drug and subject to those FDA regulations.
  • Remember that just because an ingredient is natural doesn't mean it's safe to consume.
  • Supplements, even quality ones, can negatively interact with prescription medication you're taking, so always talk to your physician about any supplements you want to take.
  • More is not necessarily better. If your doctor suggests you add vitamin D to your diet and you locate a reputable brand, take only the dosage recommended.
  • Don't take supplements in place of medication (or in addition to it) without checking with your doctor.
  • Vitamins are already added to certain foods (like milk or breakfast cereal). Adding a vitamin pill on top of this might be overkill and in some instances, actually dangerous for your health.

Be especially wary of any supplements promising to help you lose weight fast, build muscle or enhance your sexual prowess. Many of them contain very harmful ingredients, steroids or prescription drugs. In a famous case, a Chinese herb called ephedra was marketed for weight loss. Although it was a natural product, it contained a chemical called ephedrine that stimulated the nervous system and constricted blood vessels. It was linked to more than 15 deaths by 1996. However, the FDA did not ban it until 2004 after the death of a major league baseball player [sources: Couzin-Frankel].


Food vs. Dietary Supplements

In general, it's better to get your vitamins from food than from a pill. Food contains other nutrients and phytochemicals not found in supplements. woraput/Getty Images

Foodies, rejoice: Experts say it's best to get your vitamins and minerals from fresh, tasty food rather than supplements. The problem is, people (especially Americans) aren't eating all that much fresh food, instead favoring processed foods, refined grains and added sugars, all of which have little nutritional value. If you're elderly, the problem is compounded because aged bodies can't absorb nutrients as easily as young ones can. Plus, seniors often eat less food overall due to dampened appetites. In the end, many people simply are unable to get the nutrients they need from the food they eat.

Dietary supplements can help fill gaps in your diet if you don't eat a lot of nutritious food. But before you head to the supplement aisle, experts recommend first trying to eat healthier. That's because, it's not just the specific supplement you're missing — it's also how you're receiving it that matters.


Food contains many valuable nutrients as well as phytochemicals. Phytochemicals are plant chemicals that have properties that protect you from disease. The phytochemical allicin, for example, is found naturally in garlic and helps fight bacteria, while isoflavones in soy and could lessen menopausal symptoms in some women. Phytochemicals may also enhance bioavailability, which is the amount of the vitamin or mineral that your body is able to absorb. But phytochemicals are not included in supplements [sources: Berkeley Wellness, Phytochemicals].

Furthermore, food contains nutrients that help each other out. Down a frosty glass of milk and you'll be gifted not just vitamin D and various nutrients and phytochemicals, but also lactose, which helps your body absorb calcium and magnesium. If you simply took a supplement, all you'd get is the vitamin D. Also, if you take too much vitamin D (or any other supplement), it might affect your body's ability to properly absorb various nutrients.

Finally, while the nutrients in supplements and food may be chemically identical, that doesn't necessarily mean they will act the same way in your body. A study by researchers at the University of Pennsylvania School of Medicine showed the valuable Omega-3s in fatty fish were better able to maintain proper blood pressure in mice than the Omega-3 in fish oil supplements. In the study, the scientists observed how one of the fish fatty acids, docosahexaenoic acid (DHA), lowered blood pressure by dilating blood vessels at ion channels. But the DHA ethyl ester, which most fish oil supplements contain, did not dilate the blood vessels at these sites. Even worse, the DHA ethyl ester appeared to fight with the natural DHA [source: Science Daily].

So eat more fresh foods. Take only supplements recommended by your doctor and pass on the rest. And stay on top of the news for latest updates on the topic.


Lots More Information

Author's Note: How Dietary Supplements Work

I take several supplements, despite the fact that I've read plenty of horror stories over the years about various supplements that caused serious health problems in people, typically because the manufacturer wasn't reputable. But after researching this piece, I figured it would be prudent to do a little digging into the reputability of my supplement manufacturers. I'm pleased to report that all of the brands I purchase have a seal of approval from one of the independent supplement quality testers. I will always check for these in the future.

Related Articles

More Great Links

  • Berkeley Wellness. "Nutrients: They're Team Players." June 21, 2016. (March 1, 2017)
  • Consumer Reports. "The dangers of dietary and nutritional supplements investigated." September 2010. (Feb. 27, 2017)
  • Cooper, Lauren. "The Truth About Calcium and Vitamin D Supplements." Consumer Reports. July 27, 2016. (Feb. 24, 2017)
  • Council for Responsible Nutrition. "The Dietary Supplement Consumer." (Feb. 24, 2017)
  • Council for Responsible Nutrition. "Supplement Facts." (Feb. 24, 2017)
  • Couzin-Frankel, Jennifer, "Feature: Revealing the hidden dangers of dietary supplements," Science, Aug. 20, 2015
  • Globe Newswire. "Dietary Supplement Market Size Is Projected To Reach $278.02 Billion By 2024, Demand In Food & Beverage Sector: Grand View Research Inc." July 18, 2016. (Feb. 24, 2017)
  • Harvard Health Publications. "Should you get your nutrients from food or from supplements?" May 2015. (March 1, 2017)
  • Institute of Food Technologists. "Examples of Dietary Ingredients Defined as Dietary Supplements by the Dietary Supplement Health and Education Act of 1994." (March 1, 2017)
  • National Institutes of Health. "Dietary Supplements: What You Need to Know." June 17, 2011. (Feb. 27, 2017)
  • NSF. "NSF/ANSI 173: Dietary Supplements." Feb. 27, 2017. (Feb. 27, 2017)
  • Phytochemicals. "What are phytochemicals?" (March 1, 2017)
  • Prentice, R. L., et al. "Health risks and benefits from calcium and vitamin D supplementation: Women's Health Initiative clinical trial and cohort study." Springer. Feb. 2013. (Feb. 24, 2017)
  • Quality Supplements. "USP Verified Products Listing." (Feb. 27, 2017)
  • Ray, C. Claiborne. "Taking Care With Calcium Supplements." The New York Times. March 16, 2015. (March 2, 2017)
  • Reinberg, Steven. "Why Do Millions of Americans Take Multivitamins?" Web MD. Feb. 4, 2014. (Feb. 24, 2017)
  • Scarbrough, Brian. "Dietary Supplements: A Review Of United States Regulation With Emphasis On The Dietary Supplement Health And Education Act of 1994 And Subsequent Activity." Harvard Law School. April 2004. (Feb. 27, 2017)
  • Science Daily. "Why fish is better than supplements: Omega-3s from fish vs. fish oil pills better at maintaining blood pressure in mouse model." March 5, 2013. (March 1, 2017)
  • U.S. Food & Drug Administration. "Information for Consumers on Using Dietary Supplements." July 26, 2016. (Feb. 27, 2017)
  • U.S. Preventive Services Task Force. "Vitamin D and Calcium to Prevent Fractures: Preventive Medication." February 2013. (Feb. 24, 2017)