The Complete Alphabet of Health: A Guide to All Vitamins from A to U
Functions, roles and tasks — from retinol to S-methylmethionine
Vitamins are low-molecular-weight organic compounds that, in microscopic amounts, regulate virtually all biochemical processes in the body. They are not synthesized (or are synthesized insufficiently) endogenously and must come from food.
Below is a comprehensive guide to all known vitamins, grouped by solubility and biochemical kinship. For each compound we provide: key functions, daily intakes, food sources and deficiency symptoms.
Top Vitamins People Need Most
Below is a summary table of the most significant vitamins for an adult. These are key substances whose deficiency is most common and easiest to correct. A detailed description of each is in the sections below.
| Vitamin | Key Role | Daily Intake | Best Sources |
|---|---|---|---|
| Vitamin D | Bones, immunity, hormones | 600–800 IU | Cod liver oil, fatty fish, sunlight |
| Vitamin B12 | Nervous system, blood formation | 2.4 mcg | Meat, fish, eggs, milk |
| Vitamin C | Immunity, collagen, antioxidant | 90 mg | Citrus, kiwi, bell pepper |
| Vitamin B9 (folate) | Cell division, DNA | 400 mcg | Leafy greens, legumes, liver |
| Vitamin A | Vision, skin, immunity | 700–900 mcg | Liver, carrots, eggs, spinach |
| Vitamin B6 | Metabolism, nervous system | 1.3–1.7 mg | Chicken, fish, potatoes, bananas |
| Vitamin E | Antioxidant, cell membranes | 15 mg | Vegetable oils, nuts, seeds |
| Vitamin K | Blood clotting, bones | 90–120 mcg | Green vegetables, broccoli, enzymes |
Fat-Soluble Group (A, D, E, K)
Fat-soluble vitamins accumulate in the liver and fatty tissue, are excreted slowly, so uncontrolled intake can cause hypervitaminosis. Dietary fats are required for absorption.
Vitamin A (Retinol, Beta-Carotene)
| Parameter | Value |
|---|---|
| Daily intake (men) | 900 mcg RAE (retinol activity equivalent) |
| Daily intake (women) | 700 mcg RAE |
| Tolerable upper level | 3000 mcg/day (retinol) |
| Forms | Retinol (animal sources), Beta-carotene (provitamin, plant sources) |
Sources: liver, cod liver oil, egg yolk, butter; beta-carotene — carrots, pumpkin, spinach, sweet potato, apricots.
Vitamin D (D2 — Ergocalciferol, D3 — Cholecalciferol)
| Parameter | Value |
|---|---|
| Daily intake | 600–800 IU (15–20 mcg) |
| Deficiency | 25(OH)D < 20 ng/mL (50 nmol/L) |
| Insufficiency | 25(OH)D 20–30 ng/mL |
| Optimum | 30–60 ng/mL |
Vitamin E (Tocopherols and Tocotrienols)
The main fat-soluble antioxidant. Protects cell membranes from lipid peroxidation, supports reproductive function and immune response.
- Active form: alpha-tocopherol
- Daily intake: 15 mg (22.5 IU)
- Sources: vegetable oils (sunflower, olive, wheat germ), nuts, seeds, spinach, avocado
- Deficiency: rare; manifests as hemolytic anemia, peripheral neuropathy, myopathy
Vitamin K (K1 — Phylloquinone, K2 — Menaquinone)
Phylloquinone
Plant source. Provides ~90% of needs. Found in green leafy vegetables.
Menaquinone (MK-4, MK-7)
Synthesized by intestinal microflora and found in fermented foods (natto). Longer half-life.
Daily intake: 90–120 mcg. Sources: spinach, cabbage (broccoli, Brussels sprouts), greens, liver, eggs, natto.
Water-Soluble Group: B-Complex
B vitamins act as coenzymes in key metabolic reactions: energy metabolism, neurotransmitter synthesis, blood formation, DNA methylation. They do not accumulate in the body (except B12) and require regular intake.
Vitamin B1 (Thiamine)
Functions: carbohydrate metabolism, ATP synthesis, nerve impulse conduction (acetylcholine synthesis), heart function.
Intake: 1.1–1.2 mg. Sources: pork, whole grains, legumes, nuts, yeast.
Vitamin B2 (Riboflavin)
Functions: tissue respiration, flavoprotein function (FMN and FAD), skin and vision health, blood formation.
Intake: 1.1–1.3 mg. Sources: dairy products, eggs, liver, almonds, mushrooms.
Vitamin B3 (Niacin, Nicotinic Acid, Vitamin PP)
Functions: NAD/NADH synthesis for mitochondrial respiration, lipid profile regulation (lowering LDL, raising HDL), capillary dilation.
Intake: 14–16 mg (NE — niacin equivalent). Sources: meat, fish, poultry, peanuts, whole grains.
Vitamin B5 (Pantothenic Acid)
Part of Coenzyme A (CoA) — a key metabolite of the Krebs cycle. Needed for fatty acid, cholesterol, steroid hormone and neurotransmitter acetylcholine synthesis.
Intake: 5 mg. Sources: almost all foods (from Greek "pantos" — everywhere), especially liver, eggs, avocado, mushrooms.
Vitamin B6 (Pyridoxine, Pyridoxal-5-Phosphate / P-5-P)
| Parameter | Value |
|---|---|
| Daily intake | 1.3–1.7 mg |
| Upper limit (toxicity) | 100 mg/day (sensory neuropathy) |
| Active form in supplements | Pyridoxal-5-Phosphate (P-5-P) |
Sources: poultry, fish, liver, potatoes, bananas, chickpeas, whole grains.
Vitamin B7 (Biotin, Vitamin H)
Functions: carboxylation in fat and carbohydrate metabolism (gluconeogenesis, fatty acid synthesis), keratin synthesis (hair, skin and nail health).
Intake: 30 mcg. Sources: liver, eggs (yolk), nuts, seeds, sweet potato, spinach.
Vitamin B9 (Folic Acid, Folates / 5-MTHF)
Intake: 400 mcg (DFE — dietary folate equivalent), during pregnancy — 600 mcg. Sources: liver, green leafy vegetables, legumes, citrus, fortified grains.
Vitamin B12 (Cobalamin: Methyl-, Adenosyl-, Cyanocobalamin)
| Parameter | Value |
|---|---|
| Daily intake | 2.4 mcg |
| Absorption | Requires intrinsic factor (gastric parietal cell secretion) |
| Blood norm | 200–900 pg/mL |
| Optimal level | > 400–500 pg/mL |
Water-Soluble Group: Vitamin C and P
Vitamin C (Ascorbic Acid, Ascorbates)
- Intake: 90 mg (men), 75 mg (women); smoking adds +35 mg/day
- Upper limit: 2000 mg/day (osmotic diarrhea)
- Sources: citrus, kiwi, bell pepper, broccoli, strawberries, blackcurrant, sea buckthorn
- Heat lability: Destroyed when heated above 60°C and during prolonged storage
Vitamin P (Bioflavonoids: Rutin, Quercetin, Hesperidin)
Functions: strengthening capillary walls, inhibition of hyaluronidase, protection of vitamin C from oxidation (synergism), antioxidant activity.
Sources: citrus (especially white pith and zest), buckwheat, green tea, onions, apples, berries.
Vitamin-Like Substances (Conditional Vitamins)
These compounds are not vitamins in the strict sense (synthesized endogenously in sufficient amounts or have no proven avitaminosis), but have important biological functions and are often included in complex supplements.
Vitamin B4 (Choline)
Functions: precursor of acetylcholine (memory and attention neurotransmitter), phosphatidylcholine (structural component of cell membranes), methyl group donor (via betaine).
Intake: 425–550 mg. Sources: eggs (yolk — record holder), liver, soy, cauliflower.
Vitamin B8 (Inositol / Myo-Inositol)
Functions: secondary messenger in hormone signaling (insulin, FSH, TSH), receptor sensitivity support, cell membrane component (phosphatidylinositol).
Vitamin B10 (PABA / Para-aminobenzoic Acid)
Functions: participation in folic acid synthesis by intestinal microflora, skin protection from UV radiation (part of sunscreens).
Vitamin B11 / BT (L-Carnitine)
Functions: transport of long-chain fatty acids into the mitochondrial matrix for beta-oxidation. Without carnitine, fat oxidation is impossible.
Vitamin B13 (Orotic Acid)
Functions: participation in pyrimidine base synthesis (nucleic acids), tissue growth support, cardioprotective effect.
Vitamin B15 (Pangamic Acid)
Functions: improvement of tissue oxygen uptake, lipotropic effect (prevention of fatty liver infiltration).
Vitamin B17 (Amygdalin / Laetrile)
Vitamin N (Alpha-Lipoic / Thioctic Acid)
Functions: universal endogenous antioxidant (works in both aqueous and lipid environments), cofactor of mitochondrial multienzyme complexes (pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase).
Application: In diabetic polyneuropathy — 600–1200 mg/day intravenously or orally (improves insulin sensitivity and reduces neuropathic pain).
Vitamin U (S-Methylmethionine)
Functions: methylmethionine sulfonium, stimulation of GI mucosal regeneration and healing, methyl group donor.
Which vitamins are most important for the body?
All vitamins are important, but critical ones include vitamin D (deficiency in 60% of the population), vitamin B12 (especially for vegans), folic acid (B9) (for those planning pregnancy) and vitamin C (immunity, collagen). With a balanced diet, most vitamins come in sufficient amounts, but D and B12 require special attention.
Can I take all vitamins together?
Not all combinations are safe. For example, vitamin K and vitamin E in high doses can affect blood clotting. Calcium and iron compete for absorption. Fat-soluble vitamins (A, D, E, K) accumulate in the body — their overdose is more dangerous than water-soluble ones. Better to take complexes designed with compatibility in mind, or separate intake by time.
Which vitamins are needed for immunity?
Key vitamins for the immune system: vitamin D (regulates innate and adaptive immunity), vitamin C (antioxidant, supports phagocytosis), vitamin A (protection of mucous membranes), vitamin B6 (participates in immune cell synthesis) and zinc (mineral critical for immune response).
Which vitamins are absorbed better — synthetic or from food?
The body absorbs vitamins from food and synthetic analogs almost equally, but with nuances. Folic acid (synthetic B9) is absorbed better than natural folates. Vitamin E from supplements often contains only alpha-tocopherol, while food presents all 8 tocopherol forms. Beta-carotene from carrots is absorbed worse than retinol from liver. Food sources are preferable due to accompanying nutrients and synergy.
Can you overdose on vitamins?
Yes, especially fat-soluble vitamins (A, D, E, K), which accumulate in the liver and fatty tissue. Hypervitaminosis A can cause nausea, headaches and liver damage. Vitamin D overdose leads to hypercalcemia and kidney damage. Water-soluble vitamins (C, B-complex) are excreted in urine, but in very high doses (e.g., B6 > 100 mg/day) can cause neurological symptoms. Uncontrolled high-dose intake is dangerous.
Which tests should I take to check vitamin levels?
Basic minimum: 25(OH)D (vitamin D), vitamin B12 and folates (B9) in blood serum, ferritin (indirect iron marker) and homocysteine (marker of B9/B12/B6 deficiency). For deeper diagnosis: vitamin A (retinol), vitamin E (alpha-tocopherol), vitamin B6 (pyridoxal-5-phosphate) in plasma. A doctor should interpret the tests.
Is it necessary to take vitamin D in winter?
For most regions north of the 35th parallel — yes. From October to March, sunlight UV-B is insufficient for vitamin D synthesis in the skin. Recommended preventive dose: 800–2000 IU/day for adults. Before high doses, it is advisable to take a 25(OH)D test. In summer with regular sun exposure, intake can be paused.
Which vitamins do vegans need?
Strict vegans must take vitamin B12 (absent in plants) — at least 50–100 mcg/day of cyanocobalamin or 1000 mcg twice a week. It is also recommended to monitor vitamin D (if little sun), iron (non-heme absorbs worse), calcium and omega-3 (DHA/EPA) from microalgae. Iodine and zinc also require attention.
Does vitamin C really help with colds?
Regular vitamin C intake (200 mg/day) does not prevent colds, but can reduce their duration by 8–14% in adults and 18% in children according to a Cochrane review. High doses (1000–2000 mg/day) at the start of illness have not shown effectiveness. Vitamin C is most useful for people undergoing intense physical exertion (marathoners, skiers) — their cold risk is halved.
How do active forms of vitamins differ from regular ones?
Active forms are coenzyme forms that the body can use directly, without metabolic activation. Examples: pyridoxal-5-phosphate (P-5-P) instead of pyridoxine (B6), 5-methyltetrahydrofolate (5-MTHF) instead of folic acid (B9), methylcobalamin instead of cyanocobalamin (B12). Active forms are preferable for people with metabolic disorders (MTHFR mutations, liver disease). For healthy people the difference is insignificant.
Which vitamins affect hair and nail growth?
Biotin (B7) is the key vitamin for keratin synthesis, the structural protein of hair and nails. Also important: vitamin D (stimulates hair follicles), vitamin A (regulates cell renewal), iron (deficiency is a common cause of hair loss in women), zinc and omega-3. For nails, silicon and vitamin B7 are especially important. If there is no deficiency, additional doses will not speed up growth.
Why is vitamin D deficiency dangerous?
Chronic vitamin D deficiency is associated with osteoporosis (reduced bone mineral density), increased fall risk in the elderly, weakened immunity (frequent respiratory infections), autoimmune diseases (multiple sclerosis, type 1 diabetes), cardiovascular pathologies and depressive states. In children, severe deficiency causes rickets. A 25(OH)D level below 20 ng/mL is considered deficiency, 20–30 ng/mL — insufficiency.