Fat-soluble vitamins (A, D, E, K) accumulate in tissue and are toxic in excess. Even some water-soluble vitamins cause harm at high doses (e.g., B6 neuropathy, vitamin C kidney stones). Megadose vitamin therapy is not supported by clinical evidence.
The postwar vitamin boom rested on a simple and compelling pattern. Between the 1910s and 1940s, nutritional biochemists had identified the molecular causes of scurvy, rickets, beriberi, and pellagra. In every case, a missing vitamin was the culprit, and supplementing that vitamin cured the disease. The logic seemed airtight: vitamins prevent deficiency diseases, so more vitamins must mean better health. By the 1950s, that reasoning had migrated from clinical nutrition into consumer marketing, and the health food industry was selling a dream of vitality through supplementation.
Multivitamin advertisements promised energy, stamina, and resistance to illness. Grocery shelves filled with fortified cereals, enriched breads, and vitamin-spiked juices. The implicit physiological model was reassuring: the body would absorb what it needed and excrete the rest. For water-soluble vitamins like C and most of the B complex, that model holds reasonably well under ordinary conditions. The kidneys filter excess vitamins into urine, and toxicity is rare. But vitamins A, D, E, and K are fat-soluble, not water-soluble. They accumulate in fatty tissues and the liver rather than being flushed away, and the body has no efficient mechanism for disposing of the surplus.
The medical literature on vitamin A toxicity, hypervitaminosis A, was already well established by the 1940s. Arctic explorers in the early 20th century had documented violent illness after eating polar bear liver, which contains vitamin A at concentrations high enough to be acutely poisonous. Chronic overconsumption causes headaches, nausea, bone pain, liver damage, and in extreme cases, death. Yet this knowledge remained largely confined to medical journals. The public narrative was still that vitamins were benign and beneficial.
That narrative received its most influential endorsement in 1970, when Linus Pauling, a two-time Nobel laureate, published his case for megadose vitamin C therapy. Pauling recommended daily doses of 1,000 to 10,000 milligrams, far beyond the established requirement, and later extended his enthusiasm to other vitamins. His scientific prestige lent credibility to the idea that massive supplementation could prevent disease and extend life. The wellness culture of the 1970s and 1980s absorbed the message eagerly, and megavitamin therapy became a fixture of alternative health practice.
The corrective evidence arrived piecemeal. In 1983, Herbert Schaumburg and colleagues published a report in the New England Journal of Medicine describing seven patients who had developed severe sensory neuropathy from chronic vitamin B6 overconsumption. The doses were not absurdly high by supplement standards, but the nerve damage was real and disabling. Most patients improved after stopping supplementation, but the case shattered the assumption that water-soluble vitamins were universally safe.
A decade later, the Beta-Carotene and Retinol Efficacy Trial tested whether beta-carotene and vitamin A supplements could reduce lung cancer risk in smokers. The hypothesis, rooted in observational studies linking dietary antioxidants to lower cancer rates, seemed plausible. The trial was halted early in 1994 when investigators found that supplemented smokers had significantly higher lung cancer incidence than the placebo group. The intervention intended to prevent cancer appeared to be causing it.
By the time these studies appeared, the regulatory framework in the United States had already locked in a permissive standard. The Dietary Supplement Health and Education Act of 1994 classified vitamins and supplements as food, not drugs. Manufacturers were not required to prove safety or efficacy before bringing products to market. The burden of demonstrating harm fell on the Food and Drug Administration, a costly and slow process. The infrastructure of trust that Pauling and decades of vitamin marketing had built remained largely intact, even as the clinical evidence grew more cautious. The European Food Safety Authority revised its safe upper limit for vitamin B6 downward to 12 milligrams daily in 2023, a stark contrast to the 100-milligram limit set by U.S. authorities in 1998. The science has moved on. The supplement aisle has not.
Taking large doses of vitamin C prevents and cures the common cold.
Clinical trials have found no consistent evidence that vitamin C prevents colds in the general population, though it may modestly reduce duration. Megadose supplementation can cause kidney stones and other complications.
Eggs dramatically raise cholesterol and significantly increase heart disease risk. Healthy people should eat few or no eggs.
Dietary cholesterol has limited effect on blood cholesterol in most people. Eggs are nutritious. The 2015 Dietary Guidelines Advisory Committee removed the longstanding dietary cholesterol limit.
Eating carrots improves your night vision significantly.
Vitamin A deficiency can impair night vision, but eating extra carrots beyond normal dietary levels does not enhance vision in people who are not deficient. The myth was WWII propaganda to hide radar technology.
Health and biology textbooks taught that industrial pollutants and processed food additives accumulate in the body faster than the liver and kidneys can eliminate them, and that periodic fasting, juice cleanses, or herbal supplements are needed to help these organs clear the backlog.
The liver, kidneys, lungs, and skin already detoxify the body effectively. There is no scientific evidence that detox diets, cleanses, or supplements remove toxins better than these organs do.