Table 1.
Summary of major vitamer forms of each vitamin class, with brief commentary regarding bioactivity and bioavailability considerations
| Vitamin | Chemical forms | Comments |
|---|---|---|
| Vitamin A | Retinol | Approximately full bioavailability |
| Retinyl esters | Full bioavailability of retinyl acetate and palmitate | |
| Retinaldehyde | Approximately equivalent to retinol | |
| β-Carotene | ||
| α-Carotene | ||
| β-Cryptoxanthin | ||
| Vitamin D | D3, Cholecalciferol | Evidence of greater activity of D3 than D2 |
| D2, Ergocalciferol | ||
| 25-Hydroxyvitamin D forms | Lower content but higher bioavailability than parent (nonhydroxylated) vitamin D compounds | |
| Vitamin E | α-Tocopherol | α-Tocopherol exhibits primary in vivo activity. Greatest activity in natural RRR stereochemical form |
| α-Tocopheryl acetate | Acetate and other esters are fully available – common form used in fortification | |
| β-tocopherol | Primarily contributes antioxidant activity | |
| δ-tocopherol | Primarily contributes antioxidant activity | |
| γ-tocopherol | Primarily contributes antioxidant activity | |
| Tocotrienols | Primarily contributes antioxidant activity | |
| Vitamin K | Phylloquinone (K1) | Synthesized in plants – primary dietary form |
| Menaquinone-n (K2, MK-n) | Bacterial synthesis | |
| MK-4 | Synthetic; also produced in vivo from K2 sources | |
| Dihydrophylloquinone | Produced during hydrogenation of plant oils; reduced activity | |
| Menadiones (K3) | Synthetic; highly available | |
| Thiamin | Thiamin | Vitamers have equivalent activity and bioavailability |
| Thiamin phosphates | ||
| Riboflavin | Riboflavin | Riboflavin, FAD and FMN have approximately equivalent activity and bioavailability |
| Flavin mononucleotide (FMN) | ||
| Flavin adenine dinucleotide (FAD) | ||
| Minor forms | Probably contribute to activity. | |
| Niacin | Nicotinic acid | Full niacin activity |
| Nicotinamide | Full niacin activity | |
| NAD & NADP | Highly available | |
| NADH & NADPH | Apparent gastric instability | |
| Nicotinamide riboside | Probably contributes to total niacin activity in milk | |
| Bound forms of niacin | Little availability unless released by alkaline treatment | |
| Vitamin B6 | Pyridoxine | Full activity and bioavailability |
| Pyridoxal & pyridoxamine | Approximately equivalent to pyridoxine; occasionally reported to have slightly lower bioactivity | |
| B6 5’-phosphate vitamers | Similar to bioavailability to nonphosphorylated vitamers | |
| Pyridoxine-5’-β-D-glucoside | Approximately 50% (human) bioavailability | |
| 4-Pyridoxic acid | Catabolic product inactive | |
| ɛ-Pyridoxyllysine | A protein bound complex of vitamin B6 formed during food processing/storage. Partial (∼50%) bioavailability; ?-pyridoxyllysine is not detected in routine methods of vitamin B6 analysis | |
| Pantothenic acid | Pantothenic acid | Full activity and bioavailability |
| Coenzyme A | Approximately full bioavailability | |
| Pantothenol | Approximately full activity and bioavailability | |
| 4’-Phosphopantetheine | Approximately full activity and bioavailability | |
| Biotin | Biotin | Common natural form: highly available |
| Biocytin (ɛ-biotinyl lysine) | Protein form, also derived from turnover of biotin enzymes; slower absorption than free biotin | |
| Catabolic products inactive | ||
| Folate | Folic acid | Highly available in foods and supplements. High doses may exceed metabolic capacity. |
| Naturally occurring folates: | Often incomplete bioavailability probably due to food matrix and entrapment | |
| Dihydrofolate | Unstable – minor food folate | |
| Tetrahydrofolate (THF) | Common natural folate: unstable; may undergo degradation if GI tract | |
| 5-Methyltetrahydrofolate | Major naturally occurring folate vitamer | |
| 5-Formyltetrahydrofolate | Common natural folate | |
| 10-Formyltetrahydrofolate | Common natural folate | |
| 5,10-Methenyltetrahydrofolate | Common natural folate; also formed in acidic equilibrium with 10-formylTHF | |
| 5,10-Methylenetetrahydrofolate | Readily dissociates when heated to yield THF | |
| 10-Formyldihydrofolate | Oxidation product of 10-formylTHF | |
| 10-Formyl-folic acid | Oxidation product of 10-formyldihydrofolate | |
| Vitamin B12 | Cyanocobalamin | Predominant synthetic B12 vitamer |
| Methylcobalamin | Common vitamin B12 coenzyme form | |
| Adenosylcobalamin | Common vitamin B12 coenzyme form | |
| Aquacobalamin | Common in vivo form |