Vitamins

retinol

the alcohol form of vitamin A that circulates in blood bound to retinol-binding protein

• serves as the body’s main transport form

• supports immune function, reproduction, and epithelial cell maintenance

• can be reversibly converted into retinal for vision or irreversibly into retinoic acid for gene regulation

retinal

the aldehyde form required for vision, where it binds opsin proteins to form visual pigments that undergo light-induced structural changes to initiate nerve impulses for sight, especially in low-light conditions

retinyl ester

the storage form of vitamin A created when retinol is esterified with a fatty acid, stored primarily in liver stellate cells, and hydrolyzed back to retinol when the body needs vitamin A

alpha-carotene

a provitamin A carotenoid found in orange and dark-green vegetables that can be cleaved into retinal but yields less vitamin A per molecule than beta-carotene while still contributing antioxidant protection

beta-carotene

the most potent provitamin A carotenoid, symmetrically cleaved in intestinal cells to form two molecules of retinal, making it the primary plant source of vitamin A and an important antioxidant in lipid environments

B1 (thiamin)

a coenzyme essential for carbohydrate metabolism and ATP production through roles in decarboxylation reactions and nerve conduction, with deficiency causing beriberi or Wernicke-Korsakoff syndrome

B2 (riboflavin)

a precursor to the coenzymes FAD and FMN that participate in oxidation-reduction reactions of energy metabolism, fatty acid oxidation, and electron transport chain activity

B3 (niacin)

a central electron carrier required for hundreds of metabolic reactions including glycolysis, the TCA cycle, fatty acid synthesis, and DNA repair, with deficiency causing pellagra (dermatitis, diarrhea, dementia, and death)

B5 (pantothenic acid)

a component of coenzyme A and acyl carrier protein, making it essential for fatty acid synthesis and breakdown, cholesterol synthesis, steroid hormone production, and energy metabolism

B6 (pyridoxine)

a coenzyme required for amino acid metabolism, neurotransmitter synthesis, hemoglobin formation, and glycogen breakdown

B7 (biotin)

a coenzyme for carboxylase enzymes that catalyze CO₂, transfer reactions in glyconeogenesis, fatty acid synthesis, and amino acid metabolism, tightly bound to enzymes via lysine residues

B9 (folate)

a vitamin which transfers one-carbon units necessary for DNA synthesis, cell division, and red blood cell formation, making it especially critical during pregnancy for neural tube development

B12 (cobalamin)

a cobalt-containing vitamin required for methionine synthesis and fatty acid metabolism in nerve tissue, essential for myelin maintenance and red blood cell maturation, absorbed in the ileum only when bound to intrinsic factor

D2 (ergocalciferol)

a plant-derived form produced from ergosterol in fungi and yeast after UV exposure, biologically active but generally less effective than D3 at raising blood vitamin D levels

D3 (cholecalciferol)

the animal-derived and skin-synthesized form produced when UVB radiation converts 7-dehydrocholesterol in the skin, later activated through liver and kidney hydroxylation steps

7-dehydrocholesterol

a cholesterol precursor in the skin that serves as provitamin D3 and is photochemically converted into cholecalciferol upon exposure to ultraviolet B radiation

25-hydroxyvitamin D (calcidiol)

the major circulating storage form produced in the liver, reflecting overall vitamin D status and commonly measured in blood tests due to its relatively long half-life

1,25-dihydroxyvitamin D (calcitriol)

the hormonally active form produced in the kidneys that binds nuclear receptors to regulate calcium and phosphorus absorption, bone remodeling, and parathyroid hormone activity

alpha-tocopherol

the most biologically active vitamin E form in humans, preferentially retained by the liver, functioning as a lipid-soluble antioxidant that protects polyunsaturated fatty acids in cell membranes from oxidative damage

gamma-tocopherol

the most common form in many diets, particularly from plant oils, notable for its ability to neutralize reactive nitrogen species in addition to free radicals

K1 (phylloquinone)

the primary dietary form from green leafy plants, essential for hepatic synthesis of blood-clotting factors through activation of calcium-binding proteins

K2 (menaquinone)

a group of compounds produced by intestinal bacteria and found in animal and fermented foods that support extra-hepatic functions such as bone mineralization and inhibition of vascular calcification

K3 (menadione)

a synthetic vitamin K precursor that can be converted into active forms in the body but is not used in human supplements due to potential toxicity and oxidative damage

beriberi

caused by B1 (thiamin deficiency)

Wernicke-Korsakoff syndrome

caused by B1 (thiamin deficiency)

ariboflavinosis

caused by B2 (riboflavin) deficiency

pellagra

caused by B3 (niacin) deficiency

megaloblastic anemia

caused by B9 (folate) deficiency

pernicious anemia

caused by B12 (cobalamin) deficiency

scurvy

caused by vitamin C deficiency

rickets

in children, caused by vitamin D deficiency

osteomalacia

in adults, caused by vitamin D deficiency