How Dietary Supplements Work

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