You are reading Part 4 of 4 in this series.What are Quick Facts?
Most American adults report taking vitamins, minerals, or other dietary supplements, but assessments of supplements’ potential benefits and risks are complicated by many scientific and regulatory factors. Although some of these dietary supplements are recommended by doctors for populations at risk of specific nutrient deficiencies, there is little evidence that supplements benefit generally healthy people.
Supplement research should be reviewed carefully. Study designs vary widely, and new research often contradicts previous findings. Findings for specific population groups may not generalize to the whole population. Recommendations from organizations such as the Agency for Healthcare Research and Quality, the National Institutes of Health, and the U.S. Preventive Services Task Force provide reviews of high-quality evidence.
Supplements do not have to be proven effective in order to be marketed. Supplements that have been found ineffective in various clinical trials continue to be marketed for their purported health benefits.
Supplements do not have to show evidence of safety before being marketed. Companies do not have to show specific evidence of safety before selling a supplement product. Some supplements, in certain dosages and contexts, have been shown to cause harm.
Certain supplements may have unintended health effects. St. John’s wort, for example, can weaken the effects of blood thinners, and supplements that raise nitric oxide levels may cause blood pressure to drop.
Product labels may not be accurate or comprehensive. Some herbal supplement products have been found to be adulterated with fillers or tainted with pesticides and heavy metals. Other supplement labels have claimed ingredients that are not actually present, present only in trace amounts, or present in higher amounts than are listed . Still other products, including some for weight loss, men’s sexual health, and athletic performance have been found to contain unreported pharmaceutical-grade ingredients that could put people at risk of drug interactions or other side effects.
Consumers might use supplements as a substitute for proven health interventions that are known to be safe and effective, such as eating a more balanced diet or taking prescription drugs. This can allow a disease or condition to worsen or spread and can create personal and public health challenges.
American food is often highly fortified or enriched. In the United States, B vitamins are added to flour, vitamin D to milk, and iodine to salt, among other examples. These sources can help reduce deficiencies and are important factors when calculating an individual’s daily nutrient intake.
Nutrient absorption varies greatly from person to person. Some people, such as the elderly and people with Crohn’s disease, have more difficulty absorbing some nutrients, and absorption can also vary depending on timing of ingestion, the combination of food and supplements, or the form the nutrient takes in a product. All of these factors influence how much of each nutrient people need in their diets.
Nature Endocrinology’s2016 review article details the relationships between supplements and health impacts in both developing and developed countries.
A 2015 investigation in JAMA Internal Medicine revealed results from nearly 12,000 adults in the National Health and Nutrition Examination survey, addressing reasons for supplement use. A 2016 investigation in JAMA explores trends in supplement use as shown by responses to the same survey from nearly 38,000 adults.
Some dietary supplements have been found to be contaminated or even harmful. Some herbal medicines contain heavy metals or pesticides, according to this 2011 study from Science of the Total Environment, although most did not have concerning concentrations. A U.S. Preventive Services Task Force statement found harms linked to several supplements.
A 2020 Journal of Nutrition analysis discusses the state of science surrounding personalized nutrition, including the use of data analytics and diet interventions adapted to individuals’ behavior, genetics, and health.