On the grocery-store shelf, a bottle of turmeric capsules states that the product “promotes the body’s natural healthy inflammation response.” A multivitamin marketed at adults over the age of 50 claims to provide “energy and heart health support” and “anti-aging defense.” A website selling hemp oil promises “natural therapeutic benefits,” by stimulating receptors in the body involved in mood and memory.
What do these claims have in common? None are required by law to be proved true before they’re made.
Dietary supplements are regulated by the U.S. Food and Drug Administration (FDA). However, for regulatory purposes, supplements are treated like food, not drugs. They are supposed to be sold to supplement nutrients that might be lacking in a person’s diet, not to prevent or treat any medical condition.
But the Dietary Supplement Health and Education Act, commonly abbreviated as DSHEA and passed by Congress in 1994, expanded the definition of dietary supplements from vitamins and minerals to include herbal and botanical products. It also gave supplement manufacturers permission to promote their products with so-called “structure/function” statements. These statements can claim that the product supports the normal workings of the body’s organs and systems, but manufacturers do not have to provide the FDA with rigorous proof that they do so before making such claims.
In contrast, drugs sold in the U.S. must go through a long, standardized clinical trial process before they can be marketed, showing that a product improves health and that its side effects are acceptable and well understood.
Supplement makers “aren’t supposed to lie. And the FDA can go after them for supplements that don’t have what they say they have on the label,” says Marion Nestle, PhD, MPH, professor emerita of Nutrition, Food Studies and Public Health at New York University. “That does happen, but not often.”
The bar for intervention is very high, she explains, and the FDA cannot step in unless a complaint is received from the public or if people are obviously in danger from a product. “In general, the FDA leaves supplements alone, because Congress has been so clear that they want the FDA to leave supplements alone,” she continues.
Who Takes Supplements, and Do They Benefit?
Supplement use has been rising since the passage of DSHEA. The National Health and Nutrition Examination Survey found that the percentage of adults in the U.S. who used supplements rose from more than 40% in the years leading up to the Act’s passage to over half in the years 2003 to 2006.
More women than men take supplements, and most people who use supplements take them every day3. Almost half of users say they take supplements to improve their health, and less than a quarter say they take them to supplement their diet.
People who choose to take supplements tend to already be healthier than those who don’t on many measures, including weight, physical activity, and diet4. These factors complicate studies of whether specific supplements provide benefits, since people taking them usually have a head start on health.
Less than a quarter of supplement users take specific products because of a recommendation from their health care provider4, and most people who use supplements don’t tell their doctor about what products they’re taking.
The supplement industry in the U.S. is massive, with about 75,000 supplement products on the market today, pulling in $37 billion annually.
But does this widespread use do any good? By and large, the answer seems to be no. In 2006, a State-of-the-Science Conference statement from the National Institutes of Health concluded “the present evidence is insufficient to recommend either for or against the use of [multivitamin-mineral products] by the American public to prevent chronic disease.”
Many single-nutrient supplements that seemed to hold promise for improving health have not lived up to that promise when tested in large studies. For example, taking B vitamin supplements does not appear to reduce heart attacks or cancer incidence. Omega-3 fatty acids have not been shown to prevent cognitive decline or dementia, and seem to have much more limited effects on heart disease than initially hoped.
Overall, “there’s very little evidence of vitamin and mineral deficiencies in this country, but that’s what the supplement makers are trying to convince people of: that people really are not getting enough [nutrients], and they would be doing better if they were taking supplements. But there’s no evidence whatsoever that healthy people are healthier if they take supplements,” Dr. Nestle says.
The rare exceptions—besides measurable deficiencies in individual patients—are when a normal diet cannot provide enough of a specific nutrient, Dr. Nestle adds. The gold-standard example in this scenario is iodine, which would normally be missing from the diets of people in many regions of the country, and is provided through the fortification of table salt, she explains.
A shortfall of folic acid—one of the family of B vitamins—has been linked to certain birth defects, and supplementing the diets of women before and during pregnancy with folic acid reduces the occurrence of these birth defects.
But on the flip side, supplementation isn’t always harmless. For example, evidence is emerging that calcium supplements, long promoted to women for the prevention of osteoporosis, may increase the risk of heart disease.
“In general, the evidence across the board is that if you supplement a single nutrient, it’s not likely to do any good, and there’s a small possibility of harm,” says Dr. Nestle. “People believe that if vitamins are good, more vitamins are better, but there’s a fair amount of evidence that too many vitamins are not healthy,” she adds.
Interactions and Cautions
Another unappreciated risk from dietary supplements, including herbs and botanicals, is that many can interact with the way the body processes prescription drugs.
Some botanical supplements, such as St. John’s wort, have received publicity for interfering with the absorption of a wide range of medications, from antidepressants to birth control pills.
Other supplement-drug interactions aren’t as well known to the public, which makes it important for people to tell their doctor about what supplements they’re taking, explains Melinda Ring, MD, executive director of the Osher Center for Integrative Medicine at Northwestern Medicine.
For example, she adds, some heart medications or blood thinners have doses that are tightly personalized to individual patients, “so if you add in a dietary supplement with a potential for interacting, it can lead to either high or low levels of the prescription medication,” with potentially dangerous complications.
Other supplements can be risky to take before surgery, she continues. Some—even seemingly innocuous ones like fish oil—can increase the risk of bleeding during a procedure. Others may affect the nervous system, which can cause complications with anesthesia.
Direct dangers from supplements themselves are rare, but do occur. In 2004, the FDA prohibited the sale of dietary supplements containing ephedra (also called ma huang), which had been marketed for weight loss and athletic performance, due to reports of heart attack and stroke caused by the product.
In 2015, a study estimated that about 23,000 emergency department visits a year occur for adverse events related to dietary supplements, including allergic reactions, chest pain, and nausea and vomiting.
More common than direct harms from supplement ingredients are risks that dietary supplements contain contaminants, such as heavy metals or prescription drugs, explains Dr. Ring. For this reason, she cautions her patients against taking so-called glandular supplements, which are made from animal parts such as the thyroid or adrenal glands.
“They’re not supposed to have active hormones in them, but some testing has shown that in fact they do,” Dr. Ring says.
She also advises people who want to take any type of supplement to choose products made by reputable brands, which pay more attention to quality control, and to heed the dosing instructions on any product. “Those [instructions] are there for a reason,” she says.
Many people who come into Dr. Ring’s clinics are interested in or are already using supplements for a variety of reasons. She sees promise for future research looking at herbs and botanicals used by many cultures for healing purposes for millennia, but she always counsels people that a pill—whether prescription or herbal—isn’t going to be a stand-alone solution.
“For example if somebody is having irritability and fatigue and things related to chronic stress, you can’t just take an adaptogenic herb supplement to try to counteract that. You have to address the underlying stress and help somebody build the skills to feel more [resilient],” she says.
“That’s the conversation we always have. We always start with lifestyle, focusing [things like] diet, physical activity, stress management, and social connections. All of those things need to be addressed. I always tell people, just like I wouldn’t want somebody to eat fast food and then take a medication to lower their cholesterol, it’s the same thing for dietary supplements. We always start with the core of good lifestyle approaches,” she concludes.
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