How Vitamins Work: Coenzymes, Antioxidants and Hormone-Like Roles

Enzymes and their helpers

NIH's genetics glossary explains that an enzyme is a biological catalyst, almost always a protein, that speeds up a specific chemical reaction in the cell and is not destroyed in the process. [1] In the research papers cited below, a "cofactor" (or "coenzyme") is a molecule that an enzyme works with, and vitamins or their body-made forms often play that part. These are scientists' descriptions of specific vitamins; they are not a promise that a supplement helps any condition.

Public-health sources describe the same jobs in everyday terms. The NHS says thiamin helps the body break down and release energy from food, [8] and MedlinePlus says vitamin K is needed because without it blood would not coagulate normally. [9]

Antioxidants

MedlinePlus says vitamin E is an antioxidant, [10] and that vitamin C is one of many antioxidants. [11] It explains that antioxidants are nutrients that block some of the damage caused by free radicals. [11] One narrative review notes vitamin C can donate electrons and so acts as a reducing agent, which that review says accounts for its enzymatic and non-enzymatic effects. [6]

A laboratory role does not prove a health benefit from supplements. Whether antioxidant supplements prevent disease is covered separately. See Antioxidant Evidence by Use and Vitamin E Trials: Heart, Cancer and Prostate.

Hormone-like roles: vitamins A and D

A 2023 review reports that vitamin A and vitamin D metabolites (9-cis retinoic acid and 1,25-dihydroxyvitamin D3, also called calcitriol) are ligands for nuclear receptors named RAR, RXR and VDR, and that activating these receptors in human B cells affects how those immune cells mature and function. [12] In simple terms, the body converts these vitamins into signals that switch genes on or off inside cells. That review is about laboratory immune-cell biology; it does not show that taking more vitamin A or D improves immune health. For what trials found, see Vitamin D, Immune Function and Infections.

MedlinePlus also says vitamin D helps the body absorb calcium, which is needed for normal development and maintenance of healthy teeth and bones. [9]

Vitamins that work together

Several roles overlap. MedlinePlus says folate works with vitamin B12 to help form red blood cells, [9] and the NHS says B12 helps the body use folate. [8] One risk follows from this: the NHS says folic acid doses above 1 mg can mask the symptoms of B12 deficiency, which can eventually damage the nervous system if not spotted and treated. [8] Reasons like this are why a clinician or pharmacist should review any combination of supplements, especially alongside medicines (Medication Interactions).

What this page does not say

• It does not say which vitamin to take or how much.
• It does not claim that a vitamin's lab role means supplements treat or prevent a disease. Proper evidence not found for that general claim in the sources read; specific uses are covered by condition on the evidence pages, such as Vitamins and Cognition.
• Being low in a vitamin is diagnosed by a clinician with history and tests: see Vitamin Deficiency Testing.