Overview
Vitamins are organic compounds required in small amounts for normal physiological function. The human body cannot synthesize most vitamins in adequate amounts, making them essential dietary components. There are 13 essential vitamins classified into two groups based on solubility.
| Property | Fat-Soluble Vitamins | Water-Soluble Vitamins |
|---|---|---|
| Vitamins covered | A, D, E, K | B complex (8) + C |
| Solubility | Lipids and organic solvents | Water |
| Absorption | Requires bile and dietary fat | Direct absorption |
| Transport | Chylomicrons, carrier proteins | Free in bloodstream |
| Storage | Adipose tissue, liver (extensive) | Limited (except B₁₂) |
| Excretion | Bile (not urine) | Urine (when intake exceeds needs) |
| Toxicity risk | Higher (hypervitaminosis, especially A and D) | Lower (excreted, except B₆ neuropathy and B₃ niacin flush) |
| Frequency of intake | Dietary regularity over days/weeks | Regular intake (days) needed |
Fat-Soluble Vitamins
Vitamin A (Retinoids and Carotenoids)
| Aspect | Detail |
|---|---|
| Active forms | Retinol, retinal (retinaldehyde), retinoic acid |
| Provitamins | Beta-carotene, alpha-carotene, beta-cryptoxanthin (converted to retinol in body) |
| RDA (adults) | Men: 900 μg RAE/day; Women: 700 μg RAE/day |
| Tolerable Upper Limit | 3,000 μg RAE/day (preformed vitamin A) |
| Pregnancy | 770 μg RAE/day; upper limit 3,000 μg (teratogenic above this) |
Functions:
| Function | Mechanism |
|---|---|
| Vision (rhodopsin) | 11-cis-retinal + opsin → rhodopsin (dark adaptation, color vision) |
| Gene expression | Retinoic acid receptors (RAR, RXR) regulate transcription |
| Immune function | Maintains mucosal barriers, T-cell differentiation |
| Epithelial integrity | Differentiation of epithelial cells (skin, mucous membranes) |
| Reproduction | Spermatogenesis, fetal development |
| Growth and development | Bone remodeling, cell differentiation |
Food Sources:
| Food | Serving | Vitamin A (μg RAE) | % DV |
|---|---|---|---|
| Beef liver (cooked) | 85 g (3 oz) | 6,582 | 731% |
| Sweet potato (baked) | 1 medium (114 g) | 1,403 | 156% |
| Carrot (raw) | 1 medium (61 g) | 509 | 57% |
| Pumpkin (canned) | ½ cup (122 g) | 953 | 106% |
| Spinach (cooked) | ½ cup (95 g) | 573 | 64% |
| Kale (cooked) | ½ cup (65 g) | 443 | 49% |
| Butternut squash (cooked) | ½ cup (102 g) | 572 | 64% |
| Cantaloupe | ½ cup (80 g) | 135 | 15% |
| Mango | 1 medium (200 g) | 112 | 12% |
| Red bell pepper | 1 medium (120 g) | 128 | 14% |
| Egg (whole, large) | 1 (50 g) | 75 | 8% |
Deficiency:
| Condition | Description | Populations at Risk |
|---|---|---|
| Night blindness (nyctalopia) | Impaired dark adaptation (earliest sign) | Malnutrition, fat malabsorption |
| Xerophthalmia | Dry conjunctiva, Bitot spots, corneal keratomalacia | Severe deficiency (leading cause of preventable blindness in developing countries) |
| Follicular hyperkeratosis | Rough, dry skin (excess keratin) | Chronic deficiency |
| Impaired immunity | Increased infection risk (especially measles) | Children in developing world |
| Increased mortality | Measles, diarrhea, malaria | Pre-school children |
Toxicity (Hypervitaminosis A):
| Type | Cause | Symptoms |
|---|---|---|
| Acute | Single massive dose (≥25,000 μg RAE or ≥100,000 IU) | Nausea, vomiting, headache, blurred vision, muscle incoordination |
| Chronic | Daily intake >10,000 μg RAE (>30,000 IU) for months | Dry skin, hair loss, joint pain, hepatotoxicity, pseudotumor cerebri |
| Teratogenicity | Excess during pregnancy (≥3,000 μg RAE/day) | Congenital malformations (fetal retinoid syndrome) |
| Carotenodermia | High beta-carotene intake | Yellow-orange skin (harmless, reversible) |
Vitamin D (Calciferol)
| Aspect | Detail |
|---|---|
| Active form | 1,25-dihydroxyvitamin D (calcitriol) |
| Precursor | 7-dehydrocholesterol (skin) → cholecalciferol (D₃); ergocalciferol (D₂ from plants) |
| RDA (adults 19-70) | 600 IU/day (15 μg/day) |
| RDA (adults >70) | 800 IU/day (20 μg/day) |
| Tolerable Upper Limit | 4,000 IU/day (100 μg/day) |
| Endogenous synthesis | Sunlight (UVB, 290-315 nm) on skin — 10-30 min midday, 2-3x/week |
Functions:
| Function | Mechanism |
|---|---|
| Calcium absorption | Upregulates TRPV6 (intestinal calcium channel) and calbindin |
| Phosphate absorption | Intestinal sodium-phosphate cotransporter |
| Bone mineralization | Regulates calcium/phosphate deposition |
| Bone remodeling | RANKL/RANK pathway (osteoclast differentiation) |
| Immune modulation | Antimicrobial peptides (cathelicidin), T-cell regulation |
| Cell differentiation | Antiproliferative effects (cancer prevention, observational) |
Food Sources:
| Food | Serving | Vitamin D (IU) | % DV |
|---|---|---|---|
| Cod liver oil | 1 tbsp (15 mL) | 1,360 | 340% |
| Salmon (sockeye, cooked) | 85 g (3 oz) | 570 | 71% |
| Trout (rainbow, cooked) | 85 g (3 oz) | 540 | 68% |
| Tuna (canned, light) | 85 g (3 oz) | 40 | 5% |
| Sardines (canned) | 2 sardines | 47 | 6% |
| Milk (fortified) | 1 cup (240 mL) | 120 | 15% |
| Yogurt (fortified) | 6 oz (170 g) | 80 | 10% |
| Orange juice (fortified) | 1 cup (240 mL) | 100 | 13% |
| Mushrooms (UV-exposed) | ½ cup (70 g) | 366 | 46% |
| Egg yolk | 1 large (17 g yolk) | 37 | 5% |
| Beef liver (cooked) | 85 g (3 oz) | 42 | 5% |
Deficiency:
| Condition | Description |
|---|---|
| Rickets (children) | Soft, weak bones → bowing legs, delayed growth, bone pain |
| Osteomalacia (adults) | Bone softening → diffuse bone pain, muscle weakness, fractures |
| Osteoporosis | Reduced bone mineral density (long-term insufficiency) |
| Falls (elderly) | Muscle weakness (proximal myopathy) |
| Impaired immune function | Increased respiratory infections |
Risk Groups for Deficiency:
| Group | Reason |
|---|---|
| Breastfed infants (unsupplemented) | Low vitamin D in breast milk |
| Older adults | ↓ Skin synthesis efficiency, ↓ sun exposure |
| Dark skin (high melanin) | ↓ UVB absorption for vitamin D synthesis |
| Northern latitudes (>35°N) | Limited UVB in winter months |
| Obese individuals | Sequestration in adipose tissue |
| Malabsorption syndromes | Crohn’s, celiac, cystic fibrosis, short bowel |
| Sun avoidance / covered clothing | Inadequate UV exposure |
Vitamin E (Tocopherols and Tocotrienols)
| Aspect | Detail |
|---|---|
| Active form | α-Tocopherol (most bioactive) |
| Other forms | β, γ, δ tocopherols + tocotrienols (lower bioactivity) |
| RDA (adults) | 15 mg/day (22.4 IU) |
| Tolerable Upper Limit | 1,000 mg/day (1,500 IU) |
| Primary function | Lipid-soluble antioxidant (chain-breaking, peroxyl radical scavenger) |
Functions:
| Function | Mechanism |
|---|---|
| Antioxidant | Protects PUFAs in cell membranes from lipid peroxidation |
| Immune function | Enhances T-cell mediated immunity |
| Cell signaling | Inhibition of protein kinase C |
| Platelet aggregation | Inhibition (vitamin E at high doses) |
| Neurological protection | Myelin maintenance, nerve conduction |
Food Sources:
| Food | Serving | Vitamin E (mg α-TE) | % DV |
|---|---|---|---|
| Wheat germ oil | 1 tbsp (14 g) | 20.3 | 135% |
| Sunflower seeds | 30 g (¼ cup) | 9.3 | 62% |
| Almonds | 30 g (23 nuts) | 7.3 | 49% |
| Hazelnuts | 30 g (21 nuts) | 4.3 | 29% |
| Sunflower oil | 1 tbsp (14 g) | 5.6 | 37% |
| Safflower oil | 1 tbsp (14 g) | 4.6 | 31% |
| Peanuts | 30 g (28 nuts) | 2.2 | 15% |
| Spinach (cooked) | ½ cup (95 g) | 1.9 | 13% |
| Avocado | ½ fruit (100 g) | 2.1 | 14% |
| Mango | 1 medium (200 g) | 1.5 | 10% |
Deficiency:
| Condition | Description | Context |
|---|---|---|
| Peripheral neuropathy | Axonal degeneration (spinocerebellar tract) | Fat malabsorption, genetic (abetalipoproteinemia) |
| Ataxia | Loss of coordination | Severe deficiency |
| Hemolytic anemia | Red blood cell fragility | Preterm infants |
| Myopathy | Muscle weakness | Chronic deficiency |
Note: Vitamin E deficiency is extremely rare in healthy individuals. It occurs primarily with severe fat malabsorption (cystic fibrosis, Crohn’s, short bowel syndrome) or genetic defects in α-TTP (ataxia with vitamin E deficiency, AVED).
Vitamin K (Phylloquinone and Menaquinones)
| Aspect | Detail |
|---|---|
| Vitamin K₁ (phylloquinone) | Plant source, primarily in green leafy vegetables |
| Vitamin K₂ (menaquinones, MK-4 to MK-13) | Animal sources, bacterial production (gut microbiome) |
| Vitamin K₃ (menadione) | Synthetic form (no longer used in human supplements) |
| AI (adequate intake, adults) | Men: 120 μg/day; Women: 90 μg/day |
| No established UL | Low toxicity potential |
Functions:
| Function | Mechanism | Proteins Activated |
|---|---|---|
| Blood coagulation | γ-Carboxylation of clotting factors | Factors II (prothrombin), VII, IX, X; Proteins C, S, Z |
| Bone metabolism | Osteocalcin carboxylation (binds calcium to hydroxyapatite) | Osteocalcin |
| Vascular health | Matrix Gla protein (inhibits vascular calcification) | Matrix Gla protein (MGP) |
| Kidney health | Inhibition of nephrocalcinosis | Nephrocalcinosis inhibitor |
Food Sources (K₁):
| Food | Serving | Vitamin K (μg) | % DV |
|---|---|---|---|
| Kale (cooked) | ½ cup (65 g) | 531 | 443% |
| Spinach (cooked) | ½ cup (95 g) | 444 | 370% |
| Collard greens (cooked) | ½ cup (75 g) | 418 | 348% |
| Swiss chard (cooked) | ½ cup (88 g) | 286 | 238% |
| Broccoli (cooked) | ½ cup (78 g) | 110 | 92% |
| Brussels sprouts (cooked) | ½ cup (78 g) | 109 | 91% |
| Asparagus (cooked) | ½ cup (90 g) | 46 | 38% |
| Lettuce (romaine) | 1 cup (47 g) | 48 | 40% |
| Soybean oil | 1 tbsp (14 g) | 25 | 21% |
Food Sources (K₂):
| Food | Serving | K₂ Content |
|---|---|---|
| Natto (fermented soybeans) | 100 g | ~1,000 μg (MK-7) |
| Cheese (hard, aged) | 50 g | 5-50 μg (various MK) |
| Egg yolk | 1 large | 15-25 μg (MK-4) |
| Butter | 14 g (1 tbsp) | 2-5 μg (MK-4) |
| Chicken (dark meat) | 100 g | 10-15 μg (MK-4) |
| Sauerkraut | 100 g | 5-10 μg (MK-7) |
| Beef liver | 100 g | 5-10 μg (MK-4) |
Deficiency:
| Condition | Context |
|---|---|
| Bleeding diathesis (elevated INR) | Malabsorption, liver disease, antibiotic use (↓ gut bacteria) |
| Hemorrhagic disease of newborn | Low placental transfer, low milk content, sterile gut |
| Warfarin overdose | Antagonist of vitamin K cycle (intentional or inadvertent) |
| Osteoporosis (possible) | Low vitamin K associated with low bone density (observational) |
Water-Soluble Vitamins
Vitamin B₁ (Thiamin)
| Aspect | Detail |
|---|---|
| Active form | Thiamin pyrophosphate (TPP) |
| RDA (adults) | Men: 1.2 mg/day; Women: 1.1 mg/day |
| UL | Not established (low toxicity; excess excreted) |
Functions: Coenzyme in carbohydrate and amino acid metabolism (pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, transketolase, branched-chain α-keto acid dehydrogenase). Nerve conduction (membrane ion channels).
Food Sources: Pork, whole grains, enriched grains, legumes, sunflower seeds, trout, tuna, macadamia nuts.
Deficiency (Beriberi):
| Type | Features |
|---|---|
| Wet (cardiac) | High-output heart failure, peripheral vasodilation, edema |
| Dry (neurologic) | Peripheral neuropathy (symmetrical), foot drop, wrist drop |
| Cerebral (Wernicke-Korsakoff) | Confusion, ataxia, nystagmus (Wernicke); amnesia, confabulation (Korsakoff) |
| Gastrointestinal | Anorexia, constipation, abdominal discomfort |
Risk groups: Alcohol use disorder (most common in Western countries), chronic malnutrition, bariatric surgery, hyperemesis gravidarum, HIV/AIDS, dialysis.
Vitamin B₂ (Riboflavin)
| Aspect | Detail |
|---|---|
| Active forms | Flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD) |
| RDA (adults) | Men: 1.3 mg/day; Women: 1.1 mg/day |
| UL | Not established |
Functions: Coenzyme for oxidation-reduction reactions (electron transport chain, fatty acid β-oxidation, branched-chain amino acid catabolism, vitamin B₆ activation).
Food Sources: Milk, yogurt, eggs, beef liver, almonds, mushrooms, spinach, enriched grains.
Deficiency (Ariboflavinosis): Cheilitis (angular stomatitis), glossitis (magenta tongue), seborrheic dermatitis, photophobia, corneal vascularization, normocytic anemia.
Vitamin B₃ (Niacin)
| Aspect | Detail |
|---|---|
| Active forms | Nicotinamide adenine dinucleotide (NAD⁺, NADP⁺) |
| RDA (adults) | Men: 16 mg NE/day; Women: 14 mg NE/day |
| UL | 35 mg/day (for flushing form; nicotinamide has higher UL) |
| Note | Can be synthesized from tryptophan (60 mg tryptophan ≈ 1 mg NE) |
Functions: Over 400 enzymes require NAD/NADP — glycolysis, TCA cycle, fatty acid synthesis, DNA repair, PARP activity, sirtuin activation.
Food Sources: Chicken breast, beef liver, tuna, turkey, salmon, peanuts, brown rice, potatoes, green peas.
Deficiency (Pellagra):
| Feature | Description |
|---|---|
| Dermatitis | Photosensitive rash (Casal necklace on neck), symmetrical |
| Diarrhea | Inflammation of GI tract |
| Dementia | Confusion, memory loss, depression, psychosis |
| Death | If untreated (fourth D) |
Vitamin B₅ (Pantothenic Acid)
| Aspect | Detail |
|---|---|
| Active form | Coenzyme A (CoA) |
| AI (adults) | 5 mg/day |
| UL | Not established |
Functions: CoA is central to fatty acid synthesis/oxidation, TCA cycle, acetylation reactions, cholesterol synthesis, steroid hormone formation, neurotransmitter synthesis.
Food Sources: Widespread — chicken liver, sunflower seeds, avocado, mushrooms, salmon, yogurt, potatoes, eggs, whole grains.
Deficiency: Extremely rare (“burning feet syndrome” — paresthesias). Seen only in severe generalized malnutrition.
Vitamin B₆ (Pyridoxine)
| Aspect | Detail |
|---|---|
| Active form | Pyridoxal 5’-phosphate (PLP) |
| RDA (adults) | 1.3 mg/day; >50 years: 1.7 mg (men), 1.5 mg (women) |
| UL | 100 mg/day |
| Pregnancy | 1.9 mg/day (used for nausea) |
Functions: Coenzyme for >100 enzymes — amino acid metabolism (transamination, decarboxylation), heme synthesis (δ-aminolevulinic acid synthase), neurotransmitter synthesis (serotonin, dopamine, GABA, histamine), glycogen phosphorylase, steroid hormone regulation, homocysteine metabolism.
Food Sources: Chickpeas, beef liver, poultry, fish (tuna, salmon), potatoes, bananas, fortified cereals, sunflower seeds.
Deficiency: Microcytic hypochromic anemia (impaired heme synthesis), dermatitis, glossitis, depression, confusion, peripheral neuropathy. Impaired tryptophan conversion to niacin.
Toxicity: Peripheral neuropathy (sensory at doses >100 mg/day from supplements; reversible on discontinuation).
Vitamin B₇ (Biotin)
| Aspect | Detail |
|---|---|
| Active form | Biotin (enzyme-bound) |
| AI (adults) | 30 μg/day |
| UL | Not established (no known toxicity) |
Functions: Coenzyme for carboxylation reactions — acetyl-CoA carboxylase (fatty acid synthesis), propionyl-CoA carboxylase (odd-chain FA metabolism), pyruvate carboxylase (gluconeogenesis), β-methylcrotonyl-CoA carboxylase (BCAA metabolism).
Food Sources: Beef liver, eggs (yolk), salmon, avocado, pork, sweet potato, almonds, seeds, cauliflower.
Deficiency: Rare — dermatitis, alopecia, periorificial rash, neurological symptoms (depression, hallucinations), lactic acidosis. Risk factors: raw egg white consumption (avidin binds biotin), parenteral nutrition without biotin, prolonged anticonvulsant therapy, pregnancy (subclinical).
Vitamin B₉ (Folate)
| Aspect | Detail |
|---|---|
| Active form | Tetrahydrofolate (THF) |
| RDA (adults) | 400 μg DFE/day |
| Pregnancy | 600 μg DFE/day (400 μg folic acid supplement recommended) |
| Lactation | 500 μg DFE/day |
| UL (folic acid) | 1,000 μg/day (from supplements/fortified foods only) |
Functions: One-carbon transfer reactions — purine and pyrimidine (DNA/RNA) synthesis, amino acid metabolism (homocysteine → methionine), choline metabolism.
Food Sources:
| Food | Serving | Folate (μg DFE) | % DV |
|---|---|---|---|
| Beef liver (cooked) | 85 g (3 oz) | 215 | 54% |
| Lentils (cooked) | ½ cup (99 g) | 179 | 45% |
| Chickpeas (cooked) | ½ cup (82 g) | 141 | 35% |
| Asparagus (cooked) | 4 spears (60 g) | 89 | 22% |
| Spinach (cooked) | ½ cup (95 g) | 131 | 33% |
| Black-eyed peas (cooked) | ½ cup (86 g) | 105 | 26% |
| Avocado | ½ fruit (100 g) | 81 | 20% |
| Brussels sprouts (cooked) | ½ cup (78 g) | 78 | 20% |
| Fortified breakfast cereal | 1 serving | 100-400 | 25-100% |
Deficiency:
| Condition | Description |
|---|---|
| Megaloblastic anemia | Macrocytic RBCs, hypersegmented neutrophils, impaired DNA synthesis |
| Glossitis | Smooth, red tongue |
| Neural tube defects | Spina bifida, anencephaly (folate in periconceptional period prevents 50-70%) |
| Homocysteinemia | Elevated homocysteine (potential CVD risk factor) |
| Cognitive decline | Associated with low folate (elderly) |
Toxicity: High-dose folic acid (≥1,000 μg/day from supplements) may mask B₁₂ deficiency, potentially worsening neurological damage.
Vitamin B₁₂ (Cobalamin)
| Aspect | Detail |
|---|---|
| Active forms | Methylcobalamin, adenosylcobalamin |
| RDA (adults) | 2.4 μg/day |
| Absorption | Requires intrinsic factor (IF) from gastric parietal cells |
| Storage | ~2-5 mg (liver); body stores last 3-5 years |
| UL | Not established (extremely low toxicity) |
Functions: Methionine synthase (homocysteine → methionine, requires methylcobalamin), methylmalonyl-CoA mutase (odd-chain FA → succinyl-CoA, requires adenosylcobalamin), myelin sheath maintenance.
Absorption:
| Step | Site | Process |
|---|---|---|
| 1. Protein release | Stomach | HCl + pepsin releases B₁₂ from food protein |
| 2. Haptocorrin binding | Stomach | R-protein (haptocorrin) binds and protects B₁₂ |
| 3. Intrinsic factor | Duodenum | Pancreatic enzymes degrade haptocorrin; B₁₂ binds IF |
| 4. IF-B₁₂ absorption | Ileum (terminal) | Cubam receptor (cubilin + amnionless) on enterocytes |
| 5. Blood transport | Portal circulation | B₁₂ bound to transcobalamin II (holo-TC) |
Food Sources (exclusive to animal products):
| Food | Serving | Vitamin B₁₂ (μg) | % DV |
|---|---|---|---|
| Beef liver (cooked) | 85 g (3 oz) | 71 | 2,958% |
| Clams (cooked) | 85 g (3 oz) | 84 | 3,500% |
| Sardines (canned) | 85 g (3 oz) | 8 | 333% |
| Salmon (cooked) | 85 g (3 oz) | 5 | 208% |
| Tuna (canned) | 85 g (3 oz) | 2.5 | 104% |
| Beef (ground, cooked) | 85 g (3 oz) | 2.5 | 104% |
| Milk | 1 cup (240 mL) | 1.2 | 50% |
| Yogurt (plain) | 6 oz (170 g) | 0.8 | 33% |
| Egg (hard-boiled) | 1 large | 0.6 | 25% |
| Nutritional yeast (fortified) | 1 tbsp | 2-4 | 83-167% |
Deficiency:
| Condition | Description |
|---|---|
| Megaloblastic anemia | Same as folate deficiency (macrocytic anemia) |
| Peripheral neuropathy | Symmetrical paresthesias, numbness, loss of vibration sense |
| Subacute combined degeneration | Dorsal columns (vibration/proprioception loss) + corticospinal tracts (spasticity, hyperreflexia) |
| Cognitive impairment | Memory loss, confusion, dementia |
| Glossitis | Smooth, red, painful tongue |
| Psychiatric | Depression, paranoia, hallucinations |
Risk Groups:
| Group | Mechanism |
|---|---|
| Vegans/vegetarians | No dietary source (strict vegans need supplementation) |
| Older adults (≥50 years) | 10-30% have atrophic gastritis → ↓ intrinsic factor, ↓ acid release |
| Pernicious anemia | Autoimmune destruction of gastric parietal cells (autoantibodies to IF and H⁺/K⁺-ATPase) |
| Gastric bypass surgery | ↓ IF-producing cells, altered anatomy |
| Crohn’s disease (ileal) | Ileal inflammation reduces IF-B₁₂ absorption |
| Metformin use | ↓ Calcium-dependent IF-B₁₂ uptake in ileum |
| PPI/H₂ blocker use | ↓ Gastric acid reduces B₁₂ release from food |
Vitamin C (Ascorbic Acid)
| Aspect | Detail |
|---|---|
| Active form | L-Ascorbic acid (reduced form); dehydroascorbic acid (oxidized form) |
| RDA (adults) | Men: 90 mg/day; Women: 75 mg/day |
| Smokers | +35 mg/day (increased oxidative stress) |
| UL | 2,000 mg/day |
| Functions | Antioxidant, collagen synthesis, carnitine synthesis, neurotransmitter synthesis, iron absorption, immune function |
Functions:
| Function | Mechanism |
|---|---|
| Collagen synthesis | Hydroxylation of proline and lysine (vitamin C is essential cofactor for prolyl hydroxylase and lysyl hydroxylase) |
| Antioxidant | Radical scavenger (regenerates vitamin E from tocopheroxyl radical) |
| Iron absorption | Reduces Fe³⁺ to Fe²⁺ in stomach (enhances non-heme iron absorption) |
| Carnitine synthesis | Co-factor for trimethyllysine and γ-butyrobetaine hydroxylase |
| Neurotransmitter synthesis | Dopamine β-hydroxylase (norepinephrine), other neuropeptides |
| Immune function | Stimulates leukocyte function (neutrophil chemotaxis, phagocytosis, apoptosis) |
| Epigenetic regulation | Co-factor for TET enzymes and JmjC-containing histone demethylases |
Food Sources:
| Food | Serving | Vitamin C (mg) | % DV |
|---|---|---|---|
| Red bell pepper (raw) | ½ cup (75 g) | 95 | 106% |
| Orange | 1 medium (130 g) | 70 | 78% |
| Kiwi | 1 medium (69 g) | 64 | 71% |
| Broccoli (cooked) | ½ cup (78 g) | 51 | 57% |
| Strawberries | ½ cup (83 g) | 49 | 54% |
| Brussels sprouts (cooked) | ½ cup (78 g) | 48 | 53% |
| Grapefruit juice | ½ cup (120 mL) | 47 | 52% |
| Green bell pepper (raw) | ½ cup (75 g) | 60 | 67% |
| Tomato juice | ½ cup (120 mL) | 22 | 24% |
| Mango | 1 medium (200 g) | 61 | 68% |
Deficiency (Scurvy):
| Feature | Description |
|---|---|
| Gingival hyperplasia/bleeding | Swollen, bleeding gums |
| Perifollicular hemorrhages | Pinpoint hemorrhages around hair follicles |
| Ecchymoses | Easy bruising |
| Impaired wound healing | Poor collagen synthesis |
| Fatigue, malaise | Early, non-specific symptom |
| Arthralgias | Joint pain |
| Corkscrew hairs | Fractured, coiled hairs |
| Anemia | Possible contributory role (iron absorption, bleeding) |
Risk Groups: Alcohol use disorder, smoking, restrictive diets, low fruit/vegetable intake, dialysis.
Toxicity: Generally well tolerated. GI distress (diarrhea, nausea) at >2,000 mg/day. Kidney stone risk (oxalate nephrolithiasis) — vitamin C is metabolized to oxalate; caution in stone formers.
B Vitamin Interactions
| Interaction | Mechanism | Clinical Significance |
|---|---|---|
| Folate + B₁₂ | Both involved in methionine synthase (homocysteine → methionine) | Isolated B₁₂ deficiency treated with folic acid alone may worsen neurological damage |
| B₆ + B₁₂ + Folate | Homocysteine metabolism (B₆: transsulfuration pathway; B₁₂, folate: remethylation) | Combined may lower homocysteine (but mixed CVD trial results) |
| B₂ + B₆ | FMN (B₂) required for PLP (B₆) formation | B₂ deficiency can cause functional B₆ deficiency |
| B₃ (niacin) | NAD/NADP essential for energy metabolism | Interactions with multiple vitamin pathways |
Key Takeaways
| Vitamin | Solubility | Key Function | Notable Deficiency | Notable Food Source |
|---|---|---|---|---|
| A | Fat-soluble | Vision, immune, epithelial | Night blindness, xerophthalmia | Liver, sweet potato, carrots |
| D | Fat-soluble | Calcium/phosphate homeostasis | Rickets, osteomalacia | Sunlight, fatty fish, fortified milk |
| E | Fat-soluble | Antioxidant (membrane) | Peripheral neuropathy (rare) | Sunflower seeds, almonds |
| K | Fat-soluble | Coagulation, bone metabolism | Bleeding (warfin-like) | Kale, spinach, natto |
| B₁ (thiamin) | Water-soluble | Carb metabolism, nerve function | Beriberi, Wernicke-Korsakoff | Pork, whole grains, legumes |
| B₂ (riboflavin) | Water-soluble | Redox reactions | Ariboflavinosis (cheilitis, glossitis) | Milk, liver, eggs |
| B₃ (niacin) | Water-soluble | NAD/NADP synthesis | Pellagra (dermatitis, diarrhea, dementia) | Chicken, tuna, peanuts |
| B₅ (pantothenate) | Water-soluble | CoA synthesis | Extremely rare | Widespread in foods |
| B₆ (pyridoxine) | Water-soluble | Amino acid metabolism | Microcytic anemia, dermatitis | Chickpeas, liver, poultry |
| B₇ (biotin) | Water-soluble | Carboxylation reactions | Rare (avidin-induced) | Liver, eggs, avocado |
| B₉ (folate) | Water-soluble | DNA synthesis, methylation | Megaloblastic anemia, NTDs | Lentils, liver, greens |
| B₁₂ (cobalamin) | Water-soluble | Myelin, homocysteine metabolism | Pernicious anemia, neuropathy | Only animal foods (liver, clams) |
| C | Water-soluble | Collagen, antioxidant, iron absorption | Scurvy | Bell peppers, citrus, kiwi |
- The 13 essential vitamins are required for metabolism, growth, and disease prevention
- Fat-soluble vitamins (A, D, E, K) require dietary fat for absorption and are stored in tissues (higher toxicity risk)
- Water-soluble vitamins (B complex, C) require regular intake as excess is excreted (lower toxicity risk)
- Vegans must supplement B₁₂ (not found in plant foods) and may need D, iodine, and iron
- Alcohol use disorder is the leading cause of B₁ (thiamin) and B₃ (niacin) deficiency in Western countries
- Pregnancy increases requirements for folate (neural tube prevention), iron, and vitamin D
- Older adults frequently have impaired B₁₂ absorption and vitamin D synthesis