A standard one-a-day multivitamin contains 20–30 synthetic compounds delivered simultaneously at arbitrarily determined doses, in forms the body was never designed to receive all at once. The nutrients in whole food arrive embedded in a biological matrix: bound to proteins, co-packaged with cofactors, delivered in quantities the gut can regulate. A multivitamin delivers them as isolated synthetic molecules in a single bolus. The interactions between these compounds at those concentrations: competing for the same transporters, overwhelming the same enzymes, loading the same detoxification pathways simultaneously: have never been studied as a combined load. The supplement is tested ingredient by ingredient. It is never tested as the mixture it actually is.

Read the label of any major multivitamin and you will find the same synthetic compounds documented throughout this page: folic acid instead of folate (the MTHFR problem), cyanocobalamin instead of methylcobalamin (a cyanide-containing B12 precursor the liver must detoxify), vitamin D3 (cholecalciferol: the same compound used in rodenticides), retinyl palmitate (the teratogenic form of vitamin A), calcium carbonate (chalk: the arterially calcifying form), zinc oxide (poorly absorbed, and competing with copper), iron in ferrous sulfate form (the most pro-oxidant iron form, associated with constipation, gut inflammation, and free radical generation), and synthetic vitamin E as dl-alpha-tocopherol: the racemic synthetic mixture shown in large trials to increase cancer and cardiovascular mortality. None of these are what the body extracts from food. Each is the cheapest, most shelf-stable synthetic approximation of the real compound, purchased in bulk from the same chemical suppliers that manufacture industrial inputs.

The active ingredients in a multivitamin are only part of what you swallow. The remaining volume (often the majority of the tablet) consists of excipients: fillers, binders, coatings, dyes, and preservatives. Major brand multivitamins (Centrum, owned by Pfizer; One A Day, owned by Bayer) contain a documented list of ingredients with known health concerns that appear nowhere in the supplement facts panel:

You are not taking a supplement. You are taking a pharmaceutical manufacturing byproduct delivery system that contains, incidentally, some synthetic approximations of nutrients.

• FD&C Red No. 40 and Yellow No. 6: Petroleum-derived synthetic dyes linked to hyperactivity and allergic reactions, under FDA review for carcinogenicity. Red 40 is banned in several European countries. They serve no function except appearance.
• Titanium dioxide (TiO₂): White pigment used to color tablets. IARC Group 2B possible human carcinogen by inhalation. Ingested TiO₂ nanoparticles accumulate in liver, spleen, and kidneys and cause DNA damage and gut microbiome disruption in animal studies. The European Food Safety Authority (EFSA) declared it no longer safe as a food additive in 2021. It remains in US multivitamins.
• Polyethylene glycol (PEG): Petroleum derivative used as a tablet coating. PEG is contaminated with ethylene oxide and 1,4-dioxane, both probable human carcinogens per the EPA. Neither is required to be listed on the label.
• BHT (butylated hydroxytoluene): Synthetic antioxidant preventing rancidity in fat-soluble vitamins. IARC possible carcinogen. Endocrine disruptor in animal studies. Added to protect the product's shelf life, not yours.
• Hydrogenated soybean oil and modified corn starch: GMO-derived carriers for fat-soluble vitamins. Hydrogenation produces trans-fatty acid residues. Corn starch is routinely contaminated with glyphosate residues from preharvest desiccation.
• Sodium selenate: The inorganic, poorly absorbed, and toxic-at-dose selenium form used in budget multivitamins: not the selenomethionine form found in whole food.

The Iowa Women's Health Study (Mursu et al., 2011) followed 38,772 older women over 19 years and found that use of multivitamins was associated with increased total mortality. Not neutral, increased. The same study found that iron supplementation was the single strongest contributor to excess death. Folic acid, B6, magnesium, zinc, and copper supplementation were also associated with increased mortality. The effect persisted after adjustment for diet, health status, and demographics. This was published in the Archives of Internal Medicine, one of the largest and longest supplement outcome studies ever conducted. It has been largely buried by an industry generating over $50 billion annually in supplement sales.

Prenatal vitamins are prescribed to virtually every pregnant woman as essential insurance. They contain folic acid (not methylfolate), retinyl palmitate (teratogenic form of vitamin A. The FDA has warned against doses above 10,000 IU in pregnancy; many prenatals approach this threshold), iron in ferrous sulfate form (causes severe constipation, nausea, and gut microbiome disruption in pregnancy), and synthetic vitamin D3 in the same cholecalciferol form. The prenatal multivitamin that is supposed to protect the developing fetus delivers, in one daily pill, several compounds with documented fetal harm potential: to the population most vulnerable to synthetic chemical exposure at the most critical developmental window. The MTHFR issue alone (affecting 40–60% of women, preventing folic acid conversion) means a large portion of pregnant women taking prenatal vitamins are accumulating unmetabolized folic acid (UMFA) that blocks folate receptors and suppresses NK cell activity throughout pregnancy.