(CNN) Most American adults and more than a third of children use dietary supplements, according to a new study from the US Centers for Disease Control and Prevention, and those numbers have remained steady or been on the rise.
The researchers from the CDC’s National Center for Health Statistics looked only at supplement use from 2017 to March 2020. Experts say that use is probably even higher now because it grew during the Covid-19 pandemic, particularly before the arrival of vaccines and treatments, studies and surveys showed, when people were trying to boost immunity any way they could.
Around the world, the market for supplements has been growing for at least a decade.
In the US alone, it was an estimated $20.5 billion market in 2021, according to Grand View Research, a market research and consulting company.
The new study used information from National Health and Nutrition Examination Survey, a nationally representative set of surveys of the US population.
Asked about their supplement use over the previous month, 58.5% of adults said they used at least one, and 34.8% of children and adolescents had. That’s an increase from 57.6% of adults in 2017-18, although numbers among kids have stayed about the same.
The new research found some demographic consistencies: Women used dietary supplements more than men, and the more education or money someone had, the more likely they were to use a supplement.
Asian and non-Hispanic White adults used supplements more than Hispanic and non-Hispanic Black adults. Supplement use also went up with age.
Multivitamins were popular: Nearly a quarter of kids took them, and nearly a third of adults surveyed did.
More than 18% of adults took vitamin D, the next most-popular supplement.
Although supplement use remains popular with adults and children, science has not shown that they actually offer much help with health.
In 2022, the US Preventive Services Task Force, a panel of independent experts that creates guidelines around health practices, found “insufficient evidence” to recommend for or against the use of vitamins A,C or E; multivitamins with folic acid; or antioxidant combinations for the prevention of cancer or cardiovascular disease for a healthy non-pregnant adult.
Most studies find that multivitamins don’t really make people any healthier. A 2022 study in JAMA, which the task force relied on to craft its guidance, reviewed 84 studies involving nearly 700,000 people and found that multivitamin use had little or no benefit in preventing cancer, heart and lung disease or death. They provided only a small benefit for numbers of cancer cases, although the evidence was limited.
Other supplements may be harmful; the USPSTF said there was enough evidence in that study to recommend against the use of beta carotene supplements, which the body turns into vitamin A, to prevent cardiovascular disease or cancer because of a possible higher risk of mortality, cardiovascular mortality and lung cancer.
“It’s promoted as a natural product. It’s promoted as something that is different than what you’re going to get from your doctor, and the notion is that there’s no side effects because it’s all natural, and therefore it can only do good and can never do harm. You can’t beat that,” said Dr. Paul Offit, a doctor at Children’s Hospital of Philadelphia and author of “Do You Believe in Magic? Vitamins, Supplements, and All Things Natural: A Look Behind the Curtain.”
Offit said some people may benefit from extra vitamin D, which is thought to be good for bone health, because it can help the body absorb calcium and phosphorous.
There are natural ways to get vitamin D through sun exposure, although people with darker skin tend to have lower levels in their system because the pigment melanin acts like a shade. Older people also have a harder time absorbing vitamin D from the sun. Sunscreen may block it, as can windows.
People can get a good amount of vitamin D through foods like salmon and tuna and fortified drinks like orange juice and milk, but surveys show that many people’s intake does not meet the minimum daily recommendation of 10 micrograms (mcg) up to 1 year of age, 15 mcg up to age 70 and 20 mcg for adults 71 and older.
Pregnant women should take a daily supplement with 0.4 to 0.8 milligrams (400 to 800 micrograms) of folic acid to prevent neural tube birth defects, according to a recommendation from the task force.
For those who choose to take a vitamin D supplement — or any supplement, for that matter — it’s important to note that they are only loosely regulated by the US Food and Drug Administration and don’t have to meet the same strict standards as medications.
With limited regulation, investigations over the years have found several supplements to be contaminated or to not contain the same thing that is on the label.
Experts say it’s a good rule of thumb to buy only supplements that have the USP or ConsumerLab label, which means the product has been tested by the independent nonprofit US Pharmacopoeial Convention Dietary Supplement Verification Program or ConsumerLab.com. A verified product ensures that it is not contaminated with things that may hurt people, like heavy metals or microbes, and ensures that the product is what it says it is.
Also be sure to disclose that you are taking vitamins any time you go to a doctor and have to list your medication use.
“I think people don’t think of them as medicines. But some of them can interfere with therapies like a medicine can, including chemotherapies,” Offit said. “It’s really important for doctors to know what you are taking.”
