Understanding Vitamins: A Quick Overview
Vitamins are organic compounds that your body needs in small amounts to function properly. There are 13 essential vitamins, each with unique roles in keeping your body healthy. They are grouped into two categories: fat-soluble vitamins (A, D, E, and K) and water-soluble vitamins (the eight B vitamins and vitamin C).
Fat-soluble vitamins are stored in the body's fatty tissue and liver, whereas water-soluble vitamins are not stored to a significant extent. This means water-soluble vitamins need to be consumed regularly. Eating a balanced diet is the best way to obtain the vitamins you need, and supplements are not a substitute for a healthy diet.
- Fat-soluble: vitamins A, D, E, and K
- Water-soluble: vitamin C and the B-complex vitamins (B1, B2, B3, B5, B6, B7, B9, B12)
Sources: MedlinePlus (National Library of Medicine), Priority Health, Banner Health
The Eight B Vitamins: An Overview
The B vitamins are a group of eight water-soluble vitamins that play essential roles in energy production and other metabolic processes. They include thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9), and cobalamin (B12). Each has unique functions and food sources, as detailed in the sections below.
Sources: Priority Health
Vitamin A
Vitamin A is a fat-soluble vitamin important for vision, immune function, and the health of the heart, lungs, and kidneys. It comes in two forms: preformed vitamin A (retinol) found in animal products, and provitamin A carotenoids (such as beta-carotene) found in fruits and vegetables. Your body can convert beta-carotene into active vitamin A.
Sources: Priority Health
What is Vitamin A?
Vitamin A is an essential nutrient that your body needs for vision, immune function, and the health of your heart, lungs, and kidneys. It is a fat-soluble vitamin, meaning it is stored in the body's fatty tissue and liver.
Sources: Priority Health
Role of Vitamin A in the Body
Vitamin A is crucial for vision, immune function, and maintaining the health of your heart, lungs, and kidneys. It supports the normal functioning of these organs and helps your immune system fight off infections.
Sources: Priority Health
Preformed vs. Provitamin A Carotenoids
Preformed vitamin A, known as retinol, is found in animal products like liver, eggs, and dairy. Provitamin A carotenoids, such as beta-carotene, are found in colorful fruits and vegetables. Your body can convert beta-carotene into active vitamin A as needed.
Sources: Priority Health
Recommended Dietary Allowance for Adults
The recommended dietary allowance (RDA) for vitamin A is 900 mcg RAE per day for adult men and 700 mcg RAE per day for adult women.
Vitamin A Toxicity and Upper Limit
Taking very high doses of preformed vitamin A from supplements can be toxic. The upper limit from supplements is 3,000 mcg per day; higher doses may cause headaches and liver damage. Beta-carotene from foods is not associated with toxicity.
Sources: GoodRx
When to Consider a Supplement
Most adults can meet their vitamin A needs through a balanced diet. Supplements are generally not needed unless you have a deficiency or a health condition that affects absorption. If you are considering a supplement, note that beta-carotene from foods is not associated with toxicity, but high doses of preformed vitamin A can be harmful.
Sources: Priority Health
Vitamin B1 (Thiamine) – Functions and Sources
Thiamine helps your body convert carbohydrates into energy and is important for nerve function. The RDA is 1.2 mg for men and 1.1 mg for women. Food sources include pork, fish, whole grains, and legumes. No upper limit has been established for thiamine because excess is excreted in urine.
Sources: National Institute on Aging (NIH), Priority Health, BuzzRx, GoodRx
Vitamin B2 (Riboflavin) – Functions and Sources
Riboflavin helps convert food into energy and is important for growth and red blood cell production. The RDA is 1.3 mg for men and 1.1 mg for women. Food sources include eggs, organ meats, lean meats, and green vegetables. No upper limit has been established.
Sources: National Institute on Aging (NIH), Priority Health, BuzzRx, GoodRx
Vitamin B3 (Niacin) – Functions and Sources
Niacin supports energy metabolism, skin health, and nerve function. The RDA is 16 mg for men and 14 mg for women. Niacin is found in poultry, beef, pork, fish, nuts, legumes, and fortified grains. High doses from supplements can cause flushing, so the upper limit is 35 mg per day from supplements and fortified foods.
Sources: National Institute on Aging (NIH), Priority Health, BuzzRx, GoodRx
Vitamin B5 (Pantothenic Acid) – Functions and Sources
Pantothenic acid helps convert food into energy and is involved in the production of hormones and cholesterol. The adequate intake for adults is 5 mg per day. Good sources include beef, poultry, seafood, mushrooms, avocados, sweet potatoes, whole grains, and peanuts. Deficiency is extremely rare.
Sources: Priority Health, BuzzRx
Vitamin B6 (Pyridoxine) – Functions and Sources
Vitamin B6 is involved in over 100 enzyme reactions, aids metabolism, and is important for brain development during pregnancy. The RDA for adults aged 19–50 is 1.3 mg per day for both men and women. For those over 50, the RDA increases to 1.7 mg for men and 1.5 mg for women. Good sources include fish, beef liver, potatoes, other starchy vegetables, and non-citrus fruits.
Sources: Priority Health, National Institute on Aging (NIH), BuzzRx, GoodRx
Vitamin B7 (Biotin) – Functions and Sources
Biotin helps your body turn carbohydrates, fats, and proteins into energy and is essential for healthy hair and bones. The adequate intake for adults is 30 mcg per day. Whole grains, fish, egg yolks, seeds, nuts, spinach, broccoli, and sweet potatoes provide biotin. Deficiency is rare, and no upper limit has been established.
Sources: Priority Health, BuzzRx
Vitamin B9 (Folate) – Functions and Sources
Folate is important for cell division and DNA synthesis. The RDA for adults is 400 mcg DFE per day. Food sources include broccoli, Brussels sprouts, spinach, asparagus, oranges, nuts, beans, and peas.
Sources: National Institute on Aging (NIH), Priority Health, BuzzRx
Folate vs. Folic Acid: What's the Difference?
Folate is the naturally occurring form of vitamin B9 found in foods. Folic acid is the synthetic form used in supplements and fortified foods. Folic acid has a higher bioavailability than natural folate, and it is important for women of childbearing age to get enough.
Sources: BuzzRx
Recommended Dietary Allowances for Adults
The recommended dietary allowance for folate is 400 mcg DFE per day for adults. Women of childbearing age are advised to consume adequate folic acid to reduce the risk of neural tube defects.
Sources: National Institute on Aging (NIH), BuzzRx
Top Food Sources of Folate
Good food sources of folate include broccoli, Brussels sprouts, spinach, asparagus, oranges, nuts, beans, and peas.
Folate Deficiency
Folate deficiency is rare in the United States due to food fortification, but it can cause anemia and other health issues. Signs may include fatigue, weakness, and shortness of breath.
Sources: National Institute on Aging (NIH)
Upper Intake Levels
Folic acid from supplements and fortified foods has an upper limit of 1,000 mcg per day to avoid masking a vitamin B12 deficiency.
Sources: BuzzRx
Vitamin B12
Vitamin B12 is essential for DNA synthesis, red blood cell formation, and nerve health. The RDA for adults is 2.4 mcg per day. It is naturally found in animal products such as meat, fish, poultry, eggs, and milk. Vitamin B12 absorption can decrease with age, so some older adults may need supplements or fortified foods. Vegetarians and vegans may also need to rely on fortified foods or supplements.
Sources: National Institute on Aging (NIH), Priority Health, AARP, BuzzRx
What is vitamin B12 and why adults need it
Vitamin B12 is a water-soluble vitamin essential for DNA synthesis, red blood cell formation, and nerve health. Adults need it to maintain healthy nerves and blood cells, and to make DNA.
Sources: Priority Health, MedlinePlus (National Library of Medicine)
Recommended intakes for adult men and women
The recommended daily intake for vitamin B12 is 2.4 mcg for both adult men and women.
Sources: National Institute on Aging (NIH), BuzzRx
Food sources of vitamin B12
Vitamin B12 is naturally found in meat, fish, poultry, eggs, and milk. Fortified cereals can also be a source.
When a supplement may be necessary
A vitamin B12 supplement may be necessary for older adults because absorption decreases with age, and for vegetarians and vegans who do not consume animal products.
Sources: National Institute on Aging (NIH), AARP
B12 supplements
If you need a supplement, consider a product that provides the recommended daily amount and discuss with your healthcare provider which form is best for you.
Sources: BuzzRx
Special considerations for older adults and vegetarians/vegans
Older adults often have reduced stomach acid, which can decrease vitamin B12 absorption. Vegetarians and vegans do not eat animal products, which are the primary natural sources of this vitamin. For these groups, fortified foods or supplements may be necessary to meet the RDA.
Sources: National Institute on Aging (NIH), AARP
Vitamin C
Vitamin C is a water-soluble antioxidant that helps produce collagen, improves iron absorption, and supports immune function. The RDA is 90 mg per day for adult men and 75 mg per day for adult women. Smokers need an additional 35 mg per day. Good sources include citrus fruits, red and green peppers, strawberries, broccoli, tomatoes, and potatoes.
Sources: Priority Health, MedlinePlus (National Library of Medicine), GoodRx, BuzzRx
Role of Vitamin C in the Body
Vitamin C acts as an antioxidant, helps produce collagen, improves iron absorption, and supports immune function. These functions are essential for maintaining healthy tissues and defending against infections.
Sources: Priority Health, MedlinePlus (National Library of Medicine)
Vitamin C Deficiency
Severe vitamin C deficiency can lead to scurvy. Early signs include fatigue, gum disease, and poor wound healing.
Sources: Priority Health
Who May Need a Supplement
Most adults can get enough vitamin C from their diet. Smokers may need additional vitamin C because smoking increases oxidative stress.
Upper Intake Level
The tolerable upper intake level for vitamin C is 2,000 mg per day. Higher amounts may cause nausea, diarrhea, and stomach cramps.
Common Myths About Vitamin C
One common myth is that high-dose vitamin C can prevent the common cold. While vitamin C is important for immune function, taking large amounts does not prevent colds.
Sources: Priority Health
Vitamin C and Iron Absorption
Vitamin C enhances iron absorption from plant-based foods. This is helpful for people at risk of iron deficiency, such as those following a vegetarian or vegan diet.
Sources: Priority Health
Vitamin D
Vitamin D helps the body absorb calcium, which is essential for bone health. For adults ages 51–70, the recommended daily intake is at least 15 mcg (600 IU) but not more than 100 mcg (4,000 IU). For those over 70, the recommendation is at least 20 mcg (800 IU), with the same upper limit of 100 mcg (4,000 IU) per day. Vitamin D is found naturally in fatty fish (such as salmon) and is often added to fortified milk and cereals.
Sources: National Institute on Aging (NIH), Priority Health, MedlinePlus (National Library of Medicine)
Role of Vitamin D in the Body
Vitamin D plays a crucial role in helping the body absorb calcium, which is essential for maintaining strong bones. It also supports immune function.
Sources: Priority Health, MedlinePlus (National Library of Medicine)
Sources of Vitamin D: Sun, Food, and Supplements
The body can synthesize vitamin D from sun exposure. Food sources include fatty fish like salmon and fortified products such as milk and cereals. Supplements are also available, but it's important not to exceed the upper limit.
Sources: Priority Health, MedlinePlus (National Library of Medicine)
Vitamin D Deficiency: Who Is at Risk?
People at risk of vitamin D deficiency include those with limited sun exposure, older adults, and individuals with darker skin. Many adults in the U.S. may have low vitamin D levels.
Sources: National Institute on Aging (NIH)
Testing Vitamin D Levels
If you are concerned about your vitamin D status, consult your healthcare provider.
Sources: National Institute on Aging (NIH)
Choosing a Vitamin D Supplement: D2
Both forms are used in supplements, but it's best to follow your healthcare provider's recommendation.
Sources: National Institute on Aging (NIH)
Safety: upper limits and toxicity
The upper limit for vitamin D is 100 mcg (4,000 IU) per day. Taking more can lead to toxicity, which can cause nausea, weakness, and kidney damage.
Sources: National Institute on Aging (NIH)
Vitamin E
Vitamin E is a fat-soluble antioxidant that protects cells from damage. It is important for blood cell function and immune system support. The RDA for adults is 15 mg per day. Vegetable oils, nuts (such as peanuts and almonds), and leafy green vegetables are excellent sources.
Sources: National Institute on Aging (NIH), Priority Health, Southwoods Health
Forms and Vitamin
Vitamin E exists in several forms, with alpha-tocopherol being the most active in humans. Other forms like gamma-tocopherol also have antioxidant properties.
Sources: Priority Health
Who May Benefit from a Supplement
Most adults can get enough vitamin E from their diet.
Sources: National Institute on Aging (NIH)
Toxicity Risks
High doses of vitamin E supplements can increase the risk of bleeding.
Sources: GoodRx
and Medication Interactions
However, high doses may increase bleeding risk, especially when combined with blood thinners.
Sources: GoodRx
Vitamin K
Vitamin K is essential for blood clotting and bone health. The RDA is 120 mcg for men and 90 mcg for women. It is found in green leafy vegetables such as spinach, kale, broccoli, and Brussels sprouts.
Sources: National Institute on Aging (NIH), GoodRx, MedlinePlus (National Library of Medicine), Southwoods Health
What Does Vitamin K Do?
Vitamin K plays a key role in blood clotting and is important for maintaining bone health.
Sources: Southwoods Health, MedlinePlus (National Library of Medicine)
Forms: K1 and K2
Vitamin K exists in two forms: K1 (phylloquinone), found in green leafy vegetables, and K2 (menaquinone), found in animal products and fermented foods. Both are important for health.
Sources: Southwoods Health
Vitamin K
Vitamin K can reduce the effectiveness of warfarin, a blood thinner. People taking warfarin should keep their vitamin K intake consistent to maintain stable blood clotting.
Sources: National Institute on Aging (NIH)
Supplements: When
Most adults can obtain enough vitamin K from their diet. Supplements are generally not necessary unless advised by a healthcare provider, particularly for those with malabsorption issues.
Sources: National Institute on Aging (NIH)
B-Complex Supplements: When and How to Take Them
B-complex supplements contain all eight B vitamins. They may be beneficial for people with dietary restrictions, older adults, or those who have trouble absorbing B vitamins from food. Since B vitamins are water-soluble, they are generally safe, but high doses of certain B vitamins like B6 can cause nerve damage. Take them with food to minimize stomach upset, and follow the dosage on the label.
Sources: National Institute on Aging (NIH), GoodRx
Frequently asked questions
What are the differences between water-soluble and fat-soluble vitamins?
Water-soluble vitamins (the eight B vitamins and vitamin C) dissolve in water and are not stored in the body to a significant extent, so they need to be consumed regularly. Fat-soluble vitamins (A, D, E, and K) dissolve in fat and can be stored in the liver and fatty tissues, so they do not need to be consumed as frequently. However, because they are stored, excess intake can build up to toxic levels.
Sources: MedlinePlus (National Library of Medicine)What is the best time of day to take vitamins?
For fat-soluble vitamins (A, D, E, K), taking them with a meal that contains fat improves absorption. Water-soluble vitamins can be taken at any time, but some people find that taking B vitamins in the morning helps avoid potential sleep disruption. Always follow the label instructions and your healthcare provider's guidance.
Can I take too much vitamin C?
Yes. While vitamin C is water-soluble, very high doses from supplements (above 2,000 mg per day) can cause nausea, diarrhea, and stomach cramps. Stick to the recommended upper limit to avoid these side effects.
Sources: GoodRx, BuzzRxWhat is the difference between retinol and beta-carotene?
Retinol is preformed vitamin A, found in animal products like liver and eggs. Beta-carotene is a provitamin A carotenoid found in plant foods; your body converts it into active vitamin A as needed. Unlike retinol, beta-carotene is not associated with toxicity.
Sources: Priority HealthCan I get too much vitamin A from foods rich in beta-carotene?
No. High intake of beta-carotene from foods does not cause vitamin A toxicity because the body regulates conversion to active vitamin A. However, high doses of preformed vitamin A from supplements can be toxic.
Sources: GoodRxAre vitamin A supplements safe for everyone?
No. High doses of preformed vitamin A (over 3,000 mcg per day) from supplements can be toxic, causing headaches and liver damage. They can also interact with medications like isotretinoin. Always consult your healthcare provider before taking high-dose supplements.
Sources: GoodRxWhat are the early signs of vitamin A toxicity?
High doses of vitamin A can cause headaches and liver damage. If you experience these symptoms after taking vitamin A supplements, stop the supplement and consult a healthcare provider.
Sources: GoodRxHow does vitamin A interact with other medications?
High-dose vitamin A supplements can interact with medications such as isotretinoin (used for acne) and other retinoids, increasing the risk of toxicity. Always tell your provider about all supplements you take.
Sources: GoodRxSources
- Vitamins and Minerals for Older Adults — National Institute on Aging (NIH)
- The ABCs of Vitamins: 13 Essential Vitamins and Why You Need Them — Priority Health
- 9 Essential Nutrients You Need More of As You Age — AARP
- 16 Best Vitamins for Older Adults: Energy, Immune Health ... — GoodRx
- 20 Essential Vitamins and Minerals Your Body Needs — Southwoods Health
- Dietary Supplements for Older Adults — National Institute on Aging (NIH)
- Vitamins: MedlinePlus Medical Encyclopedia — MedlinePlus (National Library of Medicine)
- What Vitamins Should I Take Daily? — BuzzRx
- Vitamins Your Body Will Need as You Age — Banner Health