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A growing number of people around the world are taking dietary supplements, even though they are rarely regulated by public health entities and are often consumed without medical guidance or supervision.

Health experts and authorities frequently warn about issues associated with the long-term consumption of these herbal products, minerals, and multivitamins, especially given the lack of evidence supporting their effectiveness.

They can also interact with prescription medicines or contain unapproved ingredients that could put your health at risk. But these warnings have done little to alter market trends. In the US, where more than 60% of adults take some type of dietary supplement, according to the Centers for Disease Control and Prevention (CDC), the market for supplements was estimated at $46 billion in the year 2020. In Mexico, supplement consumption increased by 5 to 10% during the COVID-19 pandemic in 2020, according to data from the National Association of Food Supplements Industry (ANAISA).

The Top Sellers

Dietary or nutritional supplements are products that contain “dietary ingredients” to help the body get the essential nutrients it needs. As their name indicates, they’re meant to supplement — never substitute — a healthy diet.

Amino acids, enzymes, herbs, minerals, and vitamins are some of the dietary ingredients that can be found in supplements. A study published in Nutrients identified the most popular supplements based on Google search rankings as magnesium, protein, iron, calcium, vitamin D, potassium, cobalamin (a nutrient in the B vitamin complex), vitamin C, and Omega 3 fatty acids, in that order.

Other sought-after options include garlic supplements, folic acid, echinacea, ginkgo, ginseng, glucosamine, St. John’s wort, and green tea. These are sold in a variety of forms including capsules, liquids, powders, or tablets that can be taken by mouth.

Risky Promises

Dietary supplements are not subject to the same regulations as drugs and medications. While pharmaceutical products undergo exhaustive tests to guarantee their effectiveness and safety before going on the market, dietary supplements can be sold without this vetting process.

What’s more, supplement manufacturers can make claims about their products improving our health despite there being little evidence to back their promises in most cases. While supplements generally cannot be marketed as treatments or cures for a specific disease or condition, it’s not unusual to see their labels advertising immediate and promising results.

In a study published in the medical journal BMJ Open, researchers found no apparent differences in clinically measurable health outcomes between people who took multivitamin and multimineral supplements and those who didn't, even though the former self-reported better overall health.

A large study that examined multivitamin supplement intake among tens of thousands of people found that they did not reduce the risk of heart disease, cancer, or cognitive decline. A recent article in Consumer Reports that references this study adds that healthy adults who are 50 years or older simply do not need to take a multivitamin.

But in other cases, the use of dietary supplements could result in serious health complications. A study published in the Annals of Internal Medicine analyzed data from more than 27,000 adults and found that excessive calcium intake from supplements (at least 1,000mg daily) was tied to a higher risk of death from cancer.

Warnings about dietary supplements are not just linked to the fact that we don’t know exactly what’s in them. Other risks include excessive supplement consumption; mixing supplements and medications; and substituting supplements for prescription drugs.

Interactions With Prescription Drugs

People who take supplements rarely consult with their doctor or healthcare provider before doing so. They assume supplements are harmless because they are sold freely in any store or supermarket. Similarly, doctors often don’t ask their patients whether they take these products. But certain ingredients found in supplements can interact with prescription medications and impact heart function, among other vital processes:

1. Garlic supplements: They can alter the effects of blood thinners (causing bleeding), cholesterol medications (causing muscle pain), or hypertension drugs (causing dangerous dips in blood pressure.)
2. Red yeast rice supplements: Can interact with other cholesterol medications, causing muscle pain or even a breakdown of muscle that can be potentially life-threatening.
3. L-arginine supplements: Our bodies generally produce all the L-arginine they need, and obtain this amino acid via foods such as nuts, fish, red meats, grains, beans, and dairy products. It’s important to know that L-arginine supplements can interact with some medications, including blood thinners, like aspirin and warfarin; certain diuretics; and some medications for high blood pressure, erectile dysfunction, and diabetes.

When to take supplements

Given the uncertain benefits of these and other similar herbal supplements, the advice of most health professionals it to avoid them altogether. But some doctors may recommend specific vitamin or mineral supplements for their patients, when blood tests or certain symptoms indicate a deficiency. Examples include:

1. Vitamin B12 supplements: Our bodies need this nutrient to function. A vitamin B12 deficiency can happen when a person doesn’t consume enough of it or when the body has problems absorbing or storing the vitamin. Low vitamin B12 levels are sometimes found in people who don’t eat animal products, such as vegans, unless they take supplements. It’s also common in people over 60 who may have difficulties absorbing the vitamin, which is found in poultry, red meats, eggs, and dairy.
2. Vitamin D supplements: This vitamin is found in fatty fish, fortified milks, and exposure to sunlight. For some people, it may be difficult to get the recommended amount of vitamin D (800 international units or IU). If levels of this nutrient are low, a doctor may recommend supplements.
3. Iron supplements: Iron deficiencies can lead to anemia. When there isn’t enough iron in the bloodstream, the body cannot get the amount of oxygen it needs. While anemia is a common condition, many people don’t know it is caused by an iron deficiency. For women who are in their reproductive years, the most common cause of anemia is the loss of iron due to heavy menstrual bleeding or pregnancy. Doctors usually treat this condition by prescribing iron supplements or suggesting changes in their patient’s diet.

“A well-balanced diet rich in whole foods including fruits, vegetables, fish, olive oil, and nuts negates the need for any supplements," says Dr. Pieter Cohen, assistant professor of medicine at Harvard Medical School. For those who still wish to take supplements, he offers the following recommendations:

• Opt for single ingredient supplements. In products with multiple ingredients, it’s impossible to determine which substance is having an effect on our body, whether good or bad. Multiple ingredient products are also more likely to be adulterated with hidden and unapproved substances.
• Check labels for “seals of approval” from organizations verifying the quality and purity of supplements.
• Always tell your doctor about any supplement you’re taking so they can confirm whether its ingredients interact with any of your medications.

Some supplements can be beneficial when they are used correctly and when they are taken under the guidance of a health professional.