Knowledge Base / Vitamins
Vitamins A to Z
What each one does, how much you need, and where to find it.
A practical guide to all 13 essential vitamins. Compare daily recommendations, see how much common foods actually provide, and learn what to know before taking a supplement. For most healthy people a varied diet covers most needs; supplements fill specific gaps.
Quick reference
Compare daily needs, upper limits and common food sources at a glance.
| Vitamin | Main role | Daily amount | Upper limit | Food sources |
|---|---|---|---|---|
| Vitamin A | Vision in low light, immune defenses, skin | 700–900 mcg RAE | 3,000 mcg (retinol only) | Sweet potato, carrots, spinach, liver, eggs |
| Vitamin B1 | Turns carbohydrates into energy; nerves | 1.1–1.2 mg | Not established | Pork, lentils, black beans, whole grains, fortified cereals |
| Vitamin B2 | Energy production; recycles other B vitamins | 1.1–1.3 mg | Not established | Yogurt, milk, eggs, almonds, lean meat, mushrooms |
| Vitamin B3 | Builds NAD for energy and DNA repair | 14–16 mg NE | 35 mg (supplements and fortified foods) | Tuna, salmon, chicken, peanuts, brown rice |
| Vitamin B5 | Coenzyme A for fat and energy metabolism | 5 mg (AI) | Not established | Shiitake mushrooms, sunflower seeds, avocado, eggs, meat |
| Vitamin B6 | Protein metabolism, serotonin, hemoglobin | 1.3–1.7 mg | 100 mg (US); EU: 12 mg | Salmon, tuna, chickpeas, potatoes, bananas |
| Biotin | Fat, carb and protein metabolism | 30 mcg (AI) | Not established | Eggs, salmon, nuts, seeds, sweet potato |
| Folate | DNA and new cells; pregnancy | 400 mcg DFE (600 in pregnancy) | 1,000 mcg (folic acid from supplements and fortified foods) | Lentils, spinach, asparagus, beans, fortified grains |
| Vitamin B12 | Red blood cells and nerve function | 2.4 mcg | Not established | Salmon, tuna, milk, eggs, fortified plant milks |
| Vitamin C | Collagen, iron absorption, immune cells | 75–90 mg (+35 mg if you smoke) | 2,000 mg | Oranges, kiwi, broccoli, peppers, strawberries |
| Vitamin D | Calcium absorption, bones, muscles | 600–800 IU (15–20 mcg) | 4,000 IU (100 mcg) | Salmon, trout, sardines, egg yolks, fortified milk |
| Vitamin E | Antioxidant that protects cell membranes | 15 mg | 1,000 mg (supplements) | Sunflower seeds, almonds, hazelnuts, spinach, plant oils |
| Vitamin K | Blood clotting; calcium in bone | 90–120 mcg (AI) | Not established | Spinach, kale, broccoli (K1); natto, hard cheese (K2) |
General guidance for healthy adults; needs vary by age, sex, pregnancy and breastfeeding. Ranges run from women to men (for B6 and vitamin D the higher figure applies to older adults). AI = adequate intake, RAE = retinol activity equivalents, NE = niacin equivalents, DFE = dietary folate equivalents.
Upper limits for B6, C and D count all sources. For niacin, folic acid and vitamin E they apply to supplements and fortified foods only, and for vitamin A to preformed vitamin A (retinol), not beta-carotene. Planning a pregnancy? See our prenatal vitamins guide.
Explore the vitamins
Key numbers, real food amounts, who may run low and one safety point for each vitamin.
Vitamin A
Retinol, beta-carotene · Fat-soluble
Keeps your eyes adapted to dim light and supports immune defenses and skin renewal.
Daily amount: 700–900 mcg RAE|Upper limit: 3,000 mcg (retinol only)
- 1 medium baked sweet potato1,096 mcg
- 1 medium raw carrot509 mcg
- ½ cup cooked spinach472 mcg
Safety: High-dose retinol in pregnancy can harm the baby. Beta-carotene from food does not carry this risk.
Vitamin B1
Thiamine · Water-soluble
Helps turn carbohydrates into energy and keeps nerves and heart muscle working.
Daily amount: 1.1–1.2 mg|Upper limit: Not established
- 1 cup cooked lentils0.33 mg
- ½ cup cooked asparagus0.15 mg
- 3 oz cooked salmon0.13 mg
Who may run low: Heavy alcohol use, older adults, people with diabetes and people after weight-loss (bariatric) surgery.
Safety: No harm is known from food or supplements, but very high doses have not been well studied.
Vitamin B2
Riboflavin · Water-soluble
Helps cells make energy and recycles other B vitamins.
Daily amount: 1.1–1.3 mg|Upper limit: Not established
- 8 oz plain low-fat yogurt0.49 mg
- 1 cup 2% milk0.45 mg
- 1 oz almonds0.32 mg
Safety: Bright-yellow urine after B-complex supplements is harmless.
Vitamin B3
Niacin, niacinamide · Water-soluble
Part of NAD, the molecule cells use to release energy and repair DNA.
Daily amount: 14–16 mg NE|Upper limit: 35 mg (supplements and fortified foods)
- 3 oz canned light tuna8.6 mg
- 3 oz cooked salmon8.6 mg
- 1 oz dry-roasted peanuts4.1 mg
Safety: Above 35 mg from supplements, niacin often causes skin flushing. High-dose niacin for cholesterol needs a doctor's supervision.
Vitamin B5
Pantothenic acid · Water-soluble
Needed to build coenzyme A, which drives fat and energy metabolism.
Daily amount: 5 mg (AI)|Upper limit: Not established
- ½ cup cooked shiitake2.6 mg
- 1 oz sunflower seeds2.0 mg
- ½ avocado1.4 mg
Safety: Deficiency is very rare. Very large doses can cause diarrhea.
Vitamin B6
Pyridoxine · Water-soluble
Involved in more than 100 enzyme reactions, including making serotonin and hemoglobin.
Daily amount: 1.3–1.7 mg|Upper limit: 100 mg (US); EU: 12 mg
- 3 oz cooked salmon0.70 mg
- 1 medium banana0.43 mg
- 3 oz canned light tuna0.27 mg
Who may run low: People with kidney disease, autoimmune conditions such as rheumatoid arthritis, or alcohol dependence.
Safety: 100 mg is the US upper limit, not a target. Long-term high doses can damage nerves (tingling, numbness); the EU sets its limit at 12 mg a day.
Biotin
Vitamin B7 · Water-soluble
Helps enzymes process fats, carbohydrates and protein; best known for hair and nail claims.
Daily amount: 30 mcg (AI)|Upper limit: Not established
Food sources: Eggs, salmon, nuts, seeds, sweet potato
Safety: High doses can distort lab results, including thyroid and heart (troponin) tests. Tell your doctor before blood work.
Folate
Vitamin B9, folic acid · Water-soluble
Builds DNA and new cells. Enough folic acid before pregnancy lowers the risk of neural tube defects.
Daily amount: 400 mcg DFE (600 in pregnancy)|Upper limit: 1,000 mcg (folic acid from supplements and fortified foods)
- ½ cup cooked lentils179 mcg DFE
- ½ cup cooked spinach131 mcg DFE
- 4 cooked asparagus spears89 mcg DFE
Who may run low: Women who could become pregnant, people with alcohol use disorder and people with malabsorption conditions.
Safety: High folic acid intake can hide a B12 deficiency. Check B12 if you take large doses.
Daily amount: 2.4 mcg|Upper limit: Not established
- 3 oz cooked salmon3.8 mcg
- 3 oz canned light tuna2.2 mcg
- 1 cup 2% milk1.3 mcg
- 1 large egg0.6 mcg
Who may run low: Vegans, adults over 50, people with pernicious anemia or GI surgery, and long-term users of metformin or acid reducers.
Safety: No harm is known from high intakes, but low levels can go unnoticed for years.
Vitamin C
Ascorbic acid · Water-soluble
Needed to make collagen and absorb iron from plant foods; supports normal immune function.
Daily amount: 75–90 mg (+35 mg if you smoke)|Upper limit: 2,000 mg
- 1 medium orange70 mg
- 1 kiwi64 mg
- ½ cup cooked broccoli51 mg
Who may run low: Smokers and people exposed to secondhand smoke, people with a very limited diet and people on kidney dialysis.
Safety: Above 2,000 mg a day often upsets the stomach. People prone to kidney stones should avoid high doses.
Vitamin D
D3 (cholecalciferol), D2 · Fat-soluble
Lets your gut absorb calcium for bones and plays a role in muscle and immune function.
Daily amount: 600–800 IU (15–20 mcg)|Upper limit: 4,000 IU (100 mcg)
- 3 oz cooked sockeye salmon570 IU
- 1 cup fortified 2% milk120 IU
- 1 large egg44 IU
Sunlight: Your skin also makes vitamin D from UVB sunlight. How much depends on season, latitude, time of day and skin tone.
Who may run low: Breastfed infants, older adults, people with darker skin or little sun exposure, and people with obesity or fat malabsorption.
Safety: Too much raises blood calcium. Doses above 4,000 IU should follow a blood test and a doctor's advice.
Vitamin E
Alpha-tocopherol · Fat-soluble
A fat-soluble antioxidant that protects cell membranes from oxidative damage.
Daily amount: 15 mg|Upper limit: 1,000 mg (supplements)
- 1 oz sunflower seeds7.4 mg
- 1 oz almonds7.3 mg
- ½ cup cooked spinach1.9 mg
Who may run low: People with conditions that block fat absorption, such as Crohn's disease or cystic fibrosis.
Safety: High doses can increase bleeding risk, especially with blood thinners or before surgery.
Vitamin K
K1 (phylloquinone), K2 (menaquinone) · Fat-soluble
Activates proteins for blood clotting and helps direct calcium into bone.
Daily amount: 90–120 mcg (AI)|Upper limit: Not established
- 1 cup raw spinach145 mcg
- ½ cup cooked broccoli110 mcg
- 1 cup raw kale82 mcg
Safety: If you take warfarin, keep your vitamin K intake steady and talk to your doctor before supplementing.
No vitamin matches your search. Try a food (salmon), a function (bones) or a letter (B12).
Combination formulas
When one product covering several vitamins makes more sense than single supplements.
B-Complex
All eight B vitamins in one capsule. Useful when your diet is limited; not needed if you eat varied whole foods.
Multivitamins
A safety net for gaps in the diet. Look for amounts close to 100% of the Daily Value rather than mega-doses.
Prenatal Vitamins
Folic acid, iron and iodine for before, during and after pregnancy. Ideally start 3 months before trying to conceive.
Common questions
What are the 13 essential vitamins?
There are 13: vitamins A, C, D, E and K plus eight B vitamins (B1 thiamine, B2 riboflavin, B3 niacin, B5 pantothenic acid, B6, B7 biotin, B9 folate and B12). Your body cannot make enough of them, so they must come from food, sunlight (vitamin D) or supplements.
Which vitamins are fat-soluble and which are water-soluble?
Four are fat-soluble: A, D, E and K. They are stored in the liver and fat tissue, so excess can build up. The other 9 (vitamin C and the eight B vitamins) are water-soluble; most extra amounts leave in urine, except B12, which the liver stores for years.
What is the difference between RDA, AI and UL?
The RDA is the daily amount that covers the needs of about 97% of healthy people. An AI (Adequate Intake) is used when there is not enough research to set an RDA. The UL (Tolerable Upper Intake Level) is the most you can take daily without likely harm. The UL is a ceiling, not a recommended dose.
What does it mean when no upper limit is established?
It means research has not found a level at which harm reliably appears, often because there is too little data. It does not mean unlimited doses are safe. For B1, B2, B5, biotin, B12 and K, staying near the daily amount is still the sensible default.
Can you take too much of a vitamin?
Yes. Seven vitamins have an upper limit for adults: A (3,000 mcg retinol), D (4,000 IU), E (1,000 mg from supplements), C (2,000 mg), B6 (100 mg in the US), niacin (35 mg from supplements) and folic acid (1,000 mcg). Problems almost always come from supplements, not food.
What is the best time of day to take vitamins?
Take vitamins A, D, E and K with a meal that contains some fat, because fat helps your body absorb them. B vitamins are often taken in the morning because some people find them stimulating. Taking them at the same time every day matters more than the exact hour.
Do I need a vitamin supplement if I eat a balanced diet?
Most healthy adults eating varied whole foods do not need one. The main exceptions are women who may become pregnant (400 mcg folic acid daily), vegans (B12), adults over 50 (B12, often D) and people who get little sun (D).
How do I choose a vitamin supplement?
Read the Supplement Facts panel: check the serving size, the amount per serving and the % Daily Value. Around 100% DV is enough for most people; 1,000% is rarely needed. Add up the same vitamin across all your products so you do not double up, and look for third-party testing.
Which vitamins interact with medications?
The best-known interactions are vitamin K with warfarin, high-dose vitamin E with blood thinners, and biotin with lab tests. Metformin and acid reducers can lower B12 after 2 or more years of use. Always tell your doctor or pharmacist which supplements you take.
How do I know if I am low in a vitamin?
Symptoms like tiredness or tingling are too vague to diagnose on their own. A blood test is the reliable way for vitamin D (25-hydroxy vitamin D), B12 and folate. Ask your doctor before starting high doses.
Is natural or synthetic vitamin better?
It depends on the vitamin. Natural vitamin E (d-alpha-tocopherol) is about 2 times as active per milligram as synthetic (dl-alpha). Synthetic folic acid is absorbed better than food folate. For most others, the dose and form matter more than the source.