Skip to contentWillowOne's PositionsTagsWhat’s newMediaStatisticsSearch
WillowOne's Positions

Dietary Supplements

My Positions

  1. For a person eating a varied diet, most supplements do nothing measurable. Multivitamins have been tested in large randomised trials over decades and do not reduce death, heart disease or, to any useful degree, cancer.
  2. A few work, for specific people, for a specific reason: folic acid before and during early pregnancy, vitamin D in a British winter, B12 for vegans and the elderly, iron or iodine where there is a deficiency. That is treatment of a deficiency, which is medicine, and it is the exception the industry uses to sell the rule.
  3. Some are harmful at the doses sold. Beta-carotene increased lung cancer in smokers, vitamin E increased prostate cancer, and antioxidant supplements as a class may slightly raise mortality. "It can't hurt" is false.
  4. The industry is under-regulated by design. In the United States a supplement reaches the market with no proof of safety or efficacy and the regulator must prove harm afterwards, which is the burden of proof run backwards. The European rule, that a health claim must be authorised before it is made, is the right one, and it is why British labels are so oddly phrased.

Notes

  1. The big trials. The question "does a daily multivitamin help a healthy adult" has been asked properly. The Physicians' Health Study II followed fourteen thousand doctors for eleven years and found no effect on cardiovascular disease and an eight per cent reduction in cancer, which was small, marginal, and has not been reproduced. The US Preventive Services Task Force reviewed the whole literature in 2022 and found insufficient evidence for any benefit from multivitamins or single nutrients in preventing cancer or heart disease, and recommended against beta-carotene and vitamin E. The Cochrane review of antioxidant supplements, covering nearly three hundred thousand participants, found no benefit on mortality and a possible increase. The vitamin D and omega-3 trials of the late 2010s (VITAL, D-Health), which tested the two most popular remaining candidates in tens of thousands of people, found no reduction in cancer, cardiovascular events or fractures in people who were not deficient. The pattern is the one from Homeopathy: the small and badly designed studies say yes, the large and well designed ones say no.
  2. More is not better. The error underneath the industry is a linear one: if a nutrient is good, more of it must be better. Vitamins are cofactors for enzymes, and once the enzymes are saturated the surplus is excreted, stored, or does something you did not want. Beta-carotene at supplement doses increased lung cancer by about a fifth in two large trials of smokers, one of which was stopped early for harm. Vitamin E at 400 IU increased prostate cancer by seventeen per cent in a trial of thirty-five thousand men. Vitamin A in excess damages the liver and the unborn. Linus Pauling, who had two Nobel Prizes and took eighteen grams of vitamin C a day, is the standard case: the trials he inspired, including two at the Mayo Clinic, found no effect on cancer and the Cochrane review finds none on preventing colds, and his name on the bottle is the purest Appeal to Authority in the field.
  3. What is in the bottle. Because the product is not tested before sale, nobody checks. In 2015 the New York Attorney General DNA-tested herbal supplements from four national chains and found that most did not contain the plant on the label; the method was argued over, but later chemical studies found adulteration and substitution to be routine. The FDA keeps a running list of "supplements" found to contain undeclared prescription drugs, mostly sildenafil in sexual-enhancement products and sibutramine in weight-loss ones. When the industry has killed people it has been through its own products: the L-tryptophan outbreak of 1989, ephedra, which caused heart attacks and strokes for a decade before it was banned in 2004, and a weight-loss supplement that caused a cluster of liver failures in Hawaii in 2013. The pharmacy aisle, in short, has the quality control you would expect of a market in which the seller is not required to know what they are selling.
  4. How it got that way. The US Dietary Supplement Health and Education Act of 1994 was written with the industry and carried by the senator for Utah, where much of it is based. It classifies supplements as food, exempts them from pre-market approval, and allows "structure/function" claims ("supports immune health") as long as they are not claims to treat a disease, which is why every bottle carries the same claim and the same disclaimer. The industry is now worth tens of billions of dollars a year in the United States alone and more than half of American adults buy from it. In Britain the Nutrition and Health Claims Regulation requires a claim to be authorised by the European Food Safety Authority before it goes on a label, which is why your vitamin C "contributes to the normal function of the immune system" and does not "boost" it: the first is an authorised claim and the second was refused for lack of evidence. That is regulation doing its job, and the awkward grammar is the sound of it working.
  5. The exceptions, honestly. Folic acid prevents neural tube defects and should be, and in many countries is, added to flour. Vitamin D supplementation through the British winter is advised by the government's own scientific committee because the sun is not up to it. B12 is absent from plant foods and poorly absorbed in old age. Iodised salt eliminated goitre. Pregnant women, the elderly, people with malabsorption and people on restricted diets have real needs, and a GP or a blood test will tell them which. That is the model: identify a deficiency, correct it, stop. What the industry sells is the opposite: take everything, forever, in case.

Sources

  • US Preventive Services Task Force, "Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer", JAMA 327 (2022)
  • Bjelakovic, G. et al., "Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases", Cochrane Database of Systematic Reviews (2012)
  • The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group, "The Effect of Vitamin E and Beta Carotene on the Incidence of Lung Cancer", New England Journal of Medicine 330 (1994)
  • Klein, E. A. et al., "Vitamin E and the Risk of Prostate Cancer: The SELECT Trial", JAMA 306 (2011)
  • Sesso, H. D. et al. and Gaziano, J. M. et al., Physicians' Health Study II multivitamin results, JAMA 308 (2012)
  • Manson, J. E. et al., "Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease" (VITAL), New England Journal of Medicine 380 (2019)
  • Hemilä, H. and Chalker, E., "Vitamin C for preventing and treating the common cold", Cochrane Database of Systematic Reviews (2013)
  • Offit, P. A., Do You Believe in Magic? The Sense and Nonsense of Alternative Medicine (2013)
  • Scientific Advisory Committee on Nutrition, Vitamin D and Health (2016)

Also see