Dietary supplement evidence 'varies widely' with inconsistent regulations

Key takeaways:

• Dietary supplements create a lucrative market, but the evidence on individual products vary dramatically.
• Healio spoke with experts to discuss the current research on some of the most popular supplements.

A CDC report published in April 2023 revealed that supplement use commonly occurs in the United States because 58.5% of adults and 34.8% of children and adolescents had used at least one dietary supplement in the past 30 days.

Other estimates have been higher — for example, the 2023 consumer survey on dietary supplements conducted by the trade organization Council for Responsible Nutrition reported that 74% of adults in the U.S. regularly take dietary supplements and 92% believe they are essential for their health.

Additionally, in 2023, the market for dietary supplements in North America was valued at $58.56 billion, according to Grand View Research, and the projected revenue forecast for 2030 is $86.65 billion. Globally, the market was valued at $177.5 billion in 2023, and the U.S. contributed to more than a quarter of total sales.

Despite the market’s lucrative popularity, not all supplements have confirmed health benefits supported by research.

“The amount of scientific evidence on dietary supplements varies widely — there is a lot of information on some and very little on others,” Sekai Chideya, MD, MPH, program director of clinical research at NIH’s National Center for Complementary and Integrative Health, told Healio. “As the name implies, dietary supplements are intended to supplement the diet. They are not intended to treat, diagnose, prevent, or cure any diseases.” Some supplements have solid evidence backing their health claims. Folic acid, as an example, has been studied extensively, and researchers agree that it is essential for prenatal care, particularly when it comes to reducing the risk for neural tube defects. But others, like colloidal silver, are marketed as safe and effective even though they can lead to serious adverse events.

The 1994 Dietary Supplement Health and Education Act meant that products marketed as dietary supplements are not as heavily regulated by the FDA, Lewis Nelson, MD, professor and chair of the emergency medicine department and chief of the division of medical toxicology at Rutgers New Jersey Medical School, told Healio in a previous interview. As a result, although the FDA regulates dietary supplements, it does so under a different standard than more conventional drug and food products.

“Rules for manufacturing and distributing dietary supplements are less strict than those for prescription or over-the-counter drugs,” Chideya said. “Although the FDA requires that companies submit safety data about any new ingredient not sold in the U.S. in a dietary supplement before 1994, the FDA is not authorized to review dietary supplements for safety and effectiveness before they are marketed.”

So, it is essential that primary care providers discuss dietary supplement intake with their patients, according to Chideya.

“Physicians should talk with their patients about all dietary supplements they take as well as any complementary health approaches they use,” Chideya said.

Healio spoke with experts to learn more about several of the most popular dietary supplements and the validity of their health claims.

Apple cider vinegar

Made from fermented apple juice, apple cider vinegar contains various minerals, acids and vitamins, according to Chideya.

“Apple cider vinegar has gained popularity as a dietary supplement or as an ingredient in dietary supplement products,” she said.

Globally, the apple cider vinegar market is currently valued at $684.5 million, according to estimates from Future Market Insights, and is expected to reach $1.07 billion in 2034. Part of the popularity boom is due to the supplement’s purported weight loss effects, according to Chideya.

“Both as a food and a dietary supplement, it is promoted to curb appetite and help weight loss, support healthy blood sugar and cholesterol, aid digestive health, and boost the immune system,” Chideya said. “Acetic acid, a chemical compound found in vinegar, might be responsible for some of these marketed health benefits.”

Recently, a randomized clinical trial of 120 patients revealed that apple cider vinegar supplementation might be an effective dietary intervention in the management of obesity, as it led to reductions of BMI, body fat, body weight and waist-to-hip ratio over a 12-week period.

However, “there is very little scientific evidence to support the safety and effectiveness of apple cider vinegar, especially as a dietary supplement,” Chideya said.

“There is some research that acetic acid might positively impact blood sugar levels and insulin response among diabetics and improve cholesterol levels and weight loss among people with obesity,” she added. “However, the evidence is of low quality, and the studies are small.”

Apple cider vinegar may increase satiety, slow gastric emptying “and have effects upon the microbiome,” Justin Tondt, MD, an assistant professor in the department of family and community medicine at Penn State College of Medicine, told Healio.

“While small studies suggest vinegar may mildly reduce body weight, increase insulin sensitivity, and reduce postprandial glucose levels, a systematic review concluded that inadequate research of high quality exists to confirm health benefits from apple cider vinegar,” Tondt, who is also a member of the Healio Primary Care Peer Perspective Board, said. “Potential adverse effects include erosion of tooth enamel, esophagitis, and potentiating gastroparesis.”

Turmeric

Turmeric is promoted as being beneficial for a variety of conditions, including but not limited to allergies, arthritis, depression, digestive disorders, liver disease, respiratory infections and, as a paste, skin conditions, Chideya said.

“While there has been considerable research on substances made from turmeric, their health effects are uncertain,” she said. “Turmeric and curcumin have a variety of interesting biological activities, but they’re challenging to study because curcumin is unstable (it easily changes into other substances) and has low bioavailability (not much of it reaches the bloodstream) when it’s taken orally.”

Considering the complex and enigmatic mechanisms behind turmeric and its components, researchers have made no clear conclusions as to whether the supplement has health benefits, Chideya said. However, it is likely safe when taken in recommended amounts.

“Turmeric may be unsafe for use during pregnancy in amounts greater than those commonly found in food,” she cautioned. “Little is known about whether it’s safe to use turmeric in amounts greater than those commonly found in food while breastfeeding.”

Creatine

Another popular dietary supplement is creatine, an amino acid human bodies produce, Chideya said.

“It is one of the most thoroughly studied and widely used dietary supplements to enhance exercise and sports performance,” she said. “Studies in both laboratory and sports settings have found that short-term creatine supplementation —for 5 to 7 days — in both men and women often significantly increases strength and power, work involving multiple sets of maximal effort muscle contractions, and sprinting and soccer performance.”

However, Chideya said that creatine’s long-term effects have not been well studied and it can have some short-term side effects.

“There have been reports that creatine may impair liver and kidney function,” she said. “Creatine has also been linked to an increased risk of compartment syndrome, a condition where pressure builds in a muscle compartment and prevents blood flow. People at risk of kidney problems should check with their health care providers before using creatine and be carefully monitored while using it.”

Additionally, no data document safety for children and adolescents, and major organizations like the American College of Sports Medicine and the American Academy of Pediatrics have warned that teenagers should avoid “performance-enhancing supplements, including creatine, because of the possible health risks,” Chideya said.

Tondt agreed that creatine is among the dietary supplements with the most available research.

“It acts in skeletal muscle to generate cellular [adenosine triphosphate] in times of high demand,” he said. “It has been shown to be safe and effective for promoting a small increase in muscle growth compared to placebo in exercising individuals and is being investigated for a number of neuromuscular diseases.”

However, individuals can have different responses to these supplements, “possibly due to different dietary intakes of creatine,” Tondt said.

“Bloating or diarrhea are common side effects when first starting to supplement creatine,” he added. “There is controversy on its use in individuals with kidney disease.”

Fiber

Although dietary fiber can be found in fruits, vegetables, nuts, seeds and whole grains, most people in the U.S. do not get enough fiber from their diet, Chideya said.

“According to the Dietary Guidelines for Americans 2020-2025, more than 90% of women and 97% of men do not meet recommended intakes for dietary fiber,” she added. “Taking a daily fiber supplement seems to be safe.”

Chideya noted that rapid increases in dietary fiber — whether through supplementation or food — can lead to bloating, cramps and gas.

“People with gastrointestinal disorders, such as a history of blocked bowel or Crohn’s disease, or who have diabetes should talk to their health care provider before taking a fiber supplement,” she said.

Tondt said that fiber has a variety of potential effects.

“Fiber may increase sense of fullness with meals, delay carbohydrate absorption, reduce fatty liver, and increase insulin sensitivity,” he said. “While increased fiber may increase satiety and decrease body fat, the evidence is inconsistent, potentially due to the large variety in types of fiber.”

However, different types of fiber may confer varying benefits, Tondt noted.

“Viscous fiber may promote mild weight loss more effectively than other types of fiber,” he said. “Fermentable fiber may contribute to abdominal bloating or flatulence, and certain types of soluble fiber may contribute to diarrhea. Fiber from supplements should also not be conflated with fiber from foods, as fiber in foods can act as a ‘capsule’ delaying release of nutrients.”

Collagen

As one of the materials in skin, bone and cartilage, collagen is an essential protein for supporting connective tissue including tendons and ligaments, and its supplements are typically made from animal products such as bone broth, Chideya said.

“Collagen supplements are marketed to improve skin elasticity and heal wounds, improve joint pain and movement, and improve high cholesterol,” Chideya said.

There are a few types of collagen supplements, but the most common are collagen type 2 and collagen peptides, she added.

“Collagen type 2 (native) is used to improve joint stiffness, pain, and function,” Chideya said. “It has been used safely in doses up to 40 mg daily for up to 24 weeks.”

Studies suggest the supplement slightly improves function, pain and stiffness for patients who have knee osteoarthritis, but “the research is not conclusive if collagen type 2 improves symptoms of rheumatoid arthritis when compared to standard treatment,” she said.

Collagen peptides, on the other hand, “are commonly referred to as hydrolyzed collagen and collagen hydrolysate,” Chideya explained.

“There is research showing that oral collagen peptides improve skin hydration and elasticity in older adults,” she said. “Collagen peptides have been used safely up to 10 g daily for 6 months and up to 40 g daily up to 4 weeks.”

In fact, a review published in 2021 comprising 19 studies with 1,125 participants aged 20 to 70 years, 95% of whom were women, revealed that “ingestion of hydrolyzed collagen for 90 days is effective in reducing skin aging, as it reduces wrinkles and improves skin elasticity and hydration,” she said.

Although collagen is outside of his area of expertise, Tondt is skeptical of the research he has seen on muscle growth “because the positive studies have all been industry funded,” he said.

Proceed with caution

Tondt said he would generally consider these supplements to be safe.

“However, since they are unregulated, there may be contamination,” he said. “If patients choose to take them, then I advise them to look for products that have been independently tested.”

Similarly, Chideya said that, when consulting patients on dietary supplement use, it is important that PCPs keep several considerations in mind. Namely, the fact that supplements online and in stores might be different from the products tested in research studies “in important ways.”

She said many supplements have not been tested in key populations like children, nursing mothers or pregnant women. Additionally, supplements can interact with various medications or cause risks for patients going into surgery or with certain other medical problems.

“What’s listed on the label of a dietary supplement may not be what’s in the product,” she said. “For example, some products marketed for weight loss, sexual enhancement, or bodybuilding have been found to contain prescription drugs not allowed in dietary supplements or other ingredients not listed on the label, and some of these ingredients may be unsafe.”

Ultimately, Chideya said it is essential that PCPs counsel patients on what supplements may be right for them and inform them of any possible risks associated with their use.

“It is critical for people to remember that just because something is natural, or derived from nature, doesn’t mean that it cannot be harmful in high doses,” she said. “It is important to not exceed scientifically based and recommended doses of a vitamin, mineral, or supplement without first discussing it with a knowledgeable health care provider.”

References:

• Apple cider vinegar market outlook for 2024 to 2034. Available at: https://www.futuremarketinsights.com/reports/apple-cider-vinegar-market. Accessed Oct. 7, 2024.
• de Miranda RB, et al. Int J Dermatol. 2021;doi:10.1111/ijd.15518.
• Dietary supplements market size, share & trends analysis report 2024 – 2030. Available at: https://www.grandviewresearch.com/industry-analysis/dietary-supplements-market-report. Accessed Oct. 7, 2024.
• Dietary supplement use in the United States: National health and nutrition examination survey, 2017–March 2020. Available at: https://www.cdc.gov/nchs/data/nhsr/nhsr183.pdf. Published April 18, 2023. Accessed Oct. 7, 2024.
• Three-quarters of Americans take dietary supplements; most users agree they are essential to maintaining health, CRN consumer survey finds. Available at: https://www.crnusa.org/newsroom/three-quarters-americans-take-dietary-supplements-most-users-agree-they-are-essential. Published Oct. 5, 2023. Accessed Oct. 7, 2024.