Dietary supplements

Dietary supplements are vitamins, minerals, botanical extracts, amino acids, and other compounds sold for ingestion outside the drug-approval system. In the United States the category was created by statute in 1994 and treated as a kind of food: no agency reviews a product for safety or efficacy before it reaches a shelf. The category contains established medicine, chiefly the correction of documented deficiencies, wrapped in a much larger commercial layer of compounds sold for healthy aging, and the large randomized trials of that second layer have mostly returned null or harmful results.

§The regulatory bargain

The Dietary Supplement Health and Education Act of 1994 (DSHEA) defines a dietary supplement as a food rather than a drug or a food additive.¹ The consequences are structural. A manufacturer is responsible for concluding that its product is safe, but need not demonstrate that conclusion to anyone before selling it, and need not show any benefit at all. To remove a product, the Food and Drug Administration must establish that it presents a significant or unreasonable risk — after it is on the market and often after people have been hurt. Ingredients not sold in the United States before October 1994 require a pre-market notification rather than an approval, and compliance with even that is widely acknowledged to be partial.

Labels may carry structure/function claims ("supports immune health") but not disease claims ("prevents colds"), and must state that the product is not intended to diagnose, treat, cure, or prevent any disease. Good manufacturing practice rules issued in 2007 and phased in over the following years bind manufacturers on identity, purity, and record-keeping. Those rules govern process, not effect: a product can be made exactly as specified and still do nothing.

Other jurisdictions police claims more tightly without changing the underlying deal. The European Union harmonized permitted vitamin and mineral sources in 2002 and requires health claims to be authorized on a European Food Safety Authority assessment, which has left most botanical claims unresolved for over a decade. Australia lists low-risk products against a permitted-ingredients register without assessing whether they work. In none of these systems must a manufacturer produce clinical evidence of benefit before selling.

The asymmetry

A drug may not be sold until its maker has convinced a regulator that it works. A supplement may be sold until a regulator can prove that it is dangerous. That inversion of the precautionary posture applied to medicines explains most of what follows: no company needs a trial in order to sell, so almost all of the large trials have been paid for by public funders asking whether products already in millions of cabinets do anything.

§Development history

1. 1970
   Pauling popularizes megadoses
   Linus Pauling's book on vitamin C and the common cold establishes the idea that intakes far above nutritional requirement are therapeutic, a claim later trials did not support.
2. 1976
   Proxmire Amendment
   US law bars the FDA from limiting the potency of vitamin and mineral supplements or regulating them as drugs on the basis of dose alone.
3. 1994
   Beta-carotene increases lung cancer
   The Finnish ATBC trial reports higher lung cancer incidence in male smokers given beta-carotene than in those given placebo.
4. 1994
   DSHEA becomes law
   A bill sponsored by Orrin Hatch and Tom Harkin, passed after a large industry-organized public campaign, exempts supplements from pre-market approval and leaves the FDA to prove a marketed product unsafe.
5. 1996
   CARET halted early
   A second beta-carotene trial in smokers and asbestos-exposed workers is stopped ahead of schedule for excess lung cancer and higher total mortality in the supplemented arm.
6. 2004
   Ephedra banned
   After roughly a decade of adverse-event reports and several deaths, the FDA declares ephedrine-alkaloid supplements adulterated; a district court sets the rule aside before an appeals court upholds it in 2006.
7. 2007
   Manufacturing rules issued
   The FDA finalizes good manufacturing practice requirements for supplements, phased in over three years, covering identity and purity but not efficacy.
8. 2011
   SELECT reports harm
   Extended follow-up of a prostate cancer prevention trial finds significantly more prostate cancer among men who had taken vitamin E.
9. 2019
   VITAL reports null primaries
   In more than 25,000 older US adults, neither vitamin D nor marine omega-3 reduces invasive cancer or major cardiovascular events.
10. 2022
    USPSTF recommends against two
    The US Preventive Services Task Force finds the evidence insufficient for multivitamins and recommends against beta-carotene and vitamin E for preventing cancer or cardiovascular disease.

§The trial record

The antioxidant hypothesis gave the field its central prediction. If aging reflects accumulated oxidative damage, supplementing antioxidants should slow it — an idea still embedded in consumer marketing long after it stopped being how biogerontologists describe the Hallmarks of aging. Tested at scale, it did worse than null. In the Finnish ATBC trial, male smokers given beta-carotene developed more lung cancer than those given placebo.² CARET, testing beta-carotene with vitamin A in smokers and asbestos-exposed workers, was stopped early for the same reason and for higher overall mortality.³ Extended follow-up of the SELECT prostate cancer prevention trial found significantly more prostate cancer in the men who had received vitamin E.⁴ Three large trials, three findings of harm from compounds sold as protective.

The nutrients with the strongest observational associations have fared no better under randomization. VITAL enrolled more than 25,000 older US adults and tested vitamin D and marine omega-3 against placebo; neither reduced the primary cancer or cardiovascular endpoints.⁵ An ancillary study in the same cohort found no reduction in fractures either.⁶ A separate European trial of vitamin D, omega-3, and a home exercise programme in older adults found no benefit on its co-primary clinical endpoints, though a later analysis of stored samples reported that vitamin D slightly slowed several DNA-methylation age estimates. That last result is worth naming precisely: a shift in an Epigenetic clocks reading is a change in a prediction, not in an outcome, and no regulator accepts one as a surrogate.

Reviewing this literature in 2022, the US Preventive Services Task Force found the evidence insufficient to recommend multivitamins or most single nutrients to healthy adults for preventing cardiovascular disease or cancer, and recommended against beta-carotene and vitamin E outright.⁷

The multivitamin exception

A minority position holds that broad-spectrum multivitamins are the one defensible product. It rests on a US trial in male physicians reporting a small reduction in total cancer incidence, and on cognitive substudies of a later cocoa and multivitamin trial reporting modestly slower decline on test batteries in older adults. Critics answer that the effects are small and measured on continuous test scores rather than diagnoses. Defenders answer that the products are cheap and safe and that real-world nutrient intakes are not uniformly adequate. Unresolved as of 2026.

§Where supplementation is established medicine

Against a deficiency, supplementation is not contested. Iron corrects iron-deficiency anaemia; vitamin B12 corrects deficiency from malabsorption or from diets containing no animal products; vitamin D treats rickets and osteomalacia; iodine prevents goitre and developmental injury; vitamin A reduces child mortality in populations where deficiency is endemic, though the size of that effect has been disputed since a very large Indian trial reported a smaller one. Periconceptional folic acid prevents most neural tube defects, a result established by a randomized trial stopped early once the effect was clear, and one that led many countries to fortify flour.⁸

The distinction that organizes the whole subject is between restoring a deficient person to sufficiency and pushing a sufficient person higher. The first has an evidence base measured in decades. The second is what the large prevention trials tested, and it is where the record is null.

§The longevity shelf

A distinct commercial layer sells compounds for healthy aging rather than for deficiency. It includes NAD+ precursors; resveratrol, promoted through the sirtuin research programme associated with David Sinclair and since substantially deflated; flavonoids such as fisetin and quercetin, marketed on their senolytic activity against senescent cells in mice; spermidine, sold as an inducer of Autophagy and a mimetic of Caloric restriction, which produced no cognitive benefit in a randomized trial in older adults with subjective memory complaints; urolithin A, sold on mitophagy and mitochondrial decline, with small randomized trials in adults reporting changes in muscle endurance measures; and taurine, after a 2023 report in Science that supplementation extended median lifespan in mice, with human evidence limited to observational associations.

The pattern repeats: a mechanism in cells, a result in mice, a small human trial reporting a biomarker, and a product. The missing step in every case is a randomized trial with a functional endpoint in people. Marketing fills the gap with movement in a composite age estimate, which is why the absence of validated Aging biomarkers matters commercially and not only scientifically. Consumers arriving through Biohacking and grinders communities, self-tracking, and direct-to-consumer blood panels often meet a panel result and a recommended product in the same interface.

The boundary with drugs is not stable either. Metformin and the TAME trial and Rapamycin are prescription medicines used off-label toward the same goal; Nootropics straddle the line; and US law excludes from the supplement definition a compound authorized for investigation as a new drug before it was sold as a supplement, the clause at the centre of the dispute over NMN. The contrast worth holding is the GLP-1 drugs — an approved class with cardiovascular outcome trials, which is what the supplement market has never had to produce.

§Content, contamination, and harm

Independent testing repeatedly finds products that do not match their labels. Botanical products have been found substituted or diluted, most publicly in a 2015 New York attorney general action against major retailers, though that investigation's DNA-barcoding method drew criticism from analytical chemists because extraction destroys much of the DNA it looks for. Quantities deviate: an analysis of melatonin gummies sold in the United States, a product taken for sleep, found large discrepancies between labelled and measured content. The most serious failure is undeclared pharmaceuticals — sildenafil analogues in sexual-performance products, sibutramine in weight-loss products, unapproved stimulants in sports products. One study found banned drugs still present in supplements bought months after FDA recalls.⁹

Harm is not hypothetical. Supplement-related adverse events are a documented cause of emergency department visits in the United States, concentrated in cardiac symptoms among young adults taking weight-loss and energy products.¹⁰ Herbal and dietary supplements account for a growing share of cases in US drug-induced liver injury registries. Fat-soluble vitamins and selenium accumulate to toxicity. St John's wort induces drug-metabolizing enzymes and can weaken prescription medicines that people are relying on.

Strict liability in sport

Anti-doping rules hold athletes responsible for whatever is found in their bodies, regardless of intent. Contaminated or spiked supplements are a recurring source of sanctions, which is why sports bodies point athletes to third-party certification schemes. Those schemes verify identity and screen for contaminants; none of them assesses whether a product works, a distinction routinely blurred in advertising. See Enhancement in sport.

§Outlook

Nothing in the current structure creates a reason to run the missing trials. Proposals to require manufacturers to register products with the FDA have been debated for years without being enacted, and a mandatory listing would improve visibility rather than evidence. Retailer-demanded third-party verification is spreading and would address identity and contamination, which are real problems, but not efficacy.

The scientifically useful trials would look different from the ones already run: functional endpoints such as mobility, infection, or cognition rather than cancer incidence; populations selected for plausible insufficiency rather than well-nourished volunteers; and durations long enough to matter. Whether any compound on the longevity shelf survives that test is open. The record for the compounds already examined at scale is that they did not, and that two of them, beta-carotene and vitamin E, harmed some of the people who took them. The interventions with the best functional evidence for staying healthy longer, structured exercise above all, remain the ones nobody can bottle. Supplements are the most widely consumed application of the Geroscience hypothesis and the least tested.

§See also

• NAD+ precursors
• Senolytics
• Metformin and the TAME trial
• Aging biomarkers
• Exercise as a geroprotector
• Consumer blood testing
• Healthspan
• Geroscience hypothesis

§References