What are vitamins, and how do they work?

Each organism has different vitamin requirements. For example, humans need to get vitamin C from their diets — while dogs can produce all the vitamin C that they need.

Most vitamins need to come from food because the body either does not produce them or produces very little.

For humans, vitamin D is not available in large enough quantities in food. The human body synthesizes the vitamin when exposed to sunlight, and this is the best source of vitamin D.

Different vitamins play different roles in the body, and a person requires a different amount of each vitamin to stay healthy.

This article explains what vitamins are, what they do, and which foods are good sources. Follow the links in blue below for more information about each vitamin.

Share on Pinterest

Vitamins are organic substances present in minute amounts in natural foodstuffs. Having too little of any particular vitamin may increase the risk of developing certain health issues.

A vitamin is an organic compound, which means that it contains carbon. It is also an essential nutrient that the body may need to get from food.

There are currently 13 recognized vitamins.

Vitamins are either soluble, or dissolvable, in fat or water. We describe both types below:

Fat-soluble vitamins

Vitamins A, D, E, and K are fat-soluble. The body stores fat-soluble vitamins in fatty tissue and the liver, and reserves of these vitamins can stay in the body for days and sometimes months.

Dietary fats help the body absorb fat-soluble vitamins through the intestinal tract.

Water-soluble vitamins

Water-soluble vitamins do not stay in the body for long and cannot be stored. They leave the body via the urine. Because of this, people need a more regular supply of water-soluble vitamins than fat-soluble ones.

Vitamin C and all the B vitamins are water-soluble.

Below, learn about each currently recognized vitamin:

Vitamin A

Chemical names: retinol, retinal, and “the four carotenoids,” including beta carotene.

• It is fat-soluble.
• Function: It is essential for eye health.
• Deficiency: This may cause night blindness and keratomalacia, which causes the clear front layer of the eye to grow dry and cloudy.
• Good sources: These include liver, cod liver oil, carrots, broccoli, sweet potatoes, butter, kale, spinach, pumpkins, collard greens, some cheeses, eggs, apricots, cantaloupe melon, and milk.

Learn more about vitamin A.

Vitamin B1

Chemical name: thiamine.

• It is water-soluble.
• Function: It is essential for producing various enzymes that help break down blood sugar.
• Deficiency: This may cause beriberi and Wernicke-Korsakoff syndrome.
• Good sources: These include yeast, pork, cereal grains, sunflower seeds, brown rice, whole grain rye, asparagus, kale, cauliflower, potatoes, oranges, liver, and eggs.

Find out more about vitamin B1.

Vitamin B2

Chemical name: riboflavin.

• It is water-soluble.
• Function: It is essential for the growth and development of body cells and helps metabolize food.
• Deficiency: Symptoms include inflammation of the lips and fissures in the mouth.
• Good sources: These include asparagus, bananas, persimmons, okra, chard, cottage cheese, milk, yogurt, meat, eggs, fish, and green beans.

Learn more about vitamin B2.

Vitamin B3

Chemical names: niacin, niacinamide.

• It is water-soluble.
• Function: The body needs niacin for the cells to grow and work correctly.
• Deficiency: Low levels result in a health issue called pellagra, which causes diarrhea, skin changes, and intestinal upset.
• Good sources: Examples include chicken, beef, tuna, salmon, milk, eggs, tomatoes, leafy vegetables, broccoli, carrots, nuts and seeds, tofu, and lentils.

Find out more about vitamin B3.

Vitamin B5

Chemical name: pantothenic acid.

• It is water-soluble.
• Function: It is necessary for producing energy and hormones.
• Deficiency: Symptoms include paresthesia, or “pins and needles.”
• Good sources: These include meats, whole grains, broccoli, avocados, and yogurt.

Learn more here about vitamin B5.

Vitamin B6

Chemical names: pyridoxine, pyridoxamine, pyridoxal.

• It is water-soluble.
• Function: It is vital for the formation of red blood cells.
• Deficiency: Low levels may lead to anemia and peripheral neuropathy.
• Good sources: These include chickpeas, beef liver, bananas, squash, and nuts.

Find out more about vitamin B6.

Vitamin B7

Chemical name: biotin.

• It is water-soluble.
• Function: It enables the body to metabolize proteins, fats, and carbohydrates. It also contributes to keratin, a structural protein in the skin, hair, and nails.
• Deficiency: Low levels may cause dermatitis or inflammation of the intestines.
• Good sources: These include egg yolk, liver, broccoli, spinach, and cheese.

Learn more about vitamin B7.

Vitamin B9

Chemical names: folic acid, folinic acid.

• It is water-soluble.
• Functions: It is essential for making DNA and RNA.
• Deficiency: During pregnancy, this can affect the fetus’s nervous system. Doctors recommend folic acid supplements before and during pregnancy.
• Good sources: These include leafy vegetables, peas, legumes, liver, some fortified grain products, and sunflower seeds. Also, several fruits have moderate amounts.

Why is folate, another form of B9, important?

Vitamin B12

Chemical names: cyanocobalamin, hydroxocobalamin, methylcobalamin.

• It is water-soluble.
• Function: It is essential for a healthy nervous system.
• Deficiency: Low levels may lead to neurological problems and some types of anemia.
• Good sources: Examples include fish, shellfish, meat, poultry, eggs, milk and other dairy products, fortified cereals, fortified soy products, and fortified nutritional yeast.

Doctors may recommend that people with vegan diets take B12 supplements.

Why do we need vitamin B12?

Vitamin C

Chemical name: ascorbic acid.

• It is water-soluble.
• Function: It contributes to collagen production, wound healing, and bone formation. It also strengthens blood vessels, supports the immune system, helps the body absorb iron, and acts as an antioxidant.
• Deficiency: This may result in scurvy, which causes bleeding gums, a loss of teeth, and poor tissue growth and wound healing.
• Good sources: These include fruit and vegetables, but cooking destroys vitamin C.

Learn more about vitamin C.

Vitamin D

Chemical names: ergocalciferol, cholecalciferol.

• It is fat-soluble.
• Function: It is necessary for the healthy mineralization of bone.
• Deficiency: This may cause rickets and osteomalacia, or softening of the bones.
• Good sources: Exposure to UVB rays from the sun or other sources causes the body to produce vitamin D. Fatty fish, eggs, beef liver, and mushrooms also contain the vitamin.

Learn more about getting enough vitamin D.

Vitamin E

Chemical names: tocopherol, tocotrienol.

• It is fat-soluble.
• Function: Its antioxidant activity helps prevent oxidative stress, an issue that increases the risk of widespread inflammation and various diseases.
• Deficiency: This is rare, but it may cause hemolytic anemia in newborns. This condition destroys blood cells.
• Good sources: These include wheat germ, kiwis, almonds, eggs, nuts, leafy greens, and vegetable oils.

What are the symptoms of vitamin E deficiency?

Vitamin K

Chemical names: phylloquinone, menaquinone.

• It is fat-soluble.
• Function: It is necessary for blood clotting.
• Deficiency: Low levels may cause an unusual susceptibility to bleeding, or bleeding diathesis.
• Good sources: These include natto, leafy greens, pumpkins, figs, and parsley.

Why do we need vitamin K?

Many people in the United States take multivitamins and other supplements, though these may not be necessary or helpful, according to research.

A balanced, varied diet that contains plenty of fruits and vegetables should be the primary source of vitamins. The Department of Health and Human Services provide up-to-date guidelines detailing the best ways to get enough nutrients from the diet.

Fortified foods and supplements may be appropriate in some cases, however, such as during pregnancy, for people with restricted diets, and for people with specific health issues.

Anyone taking supplements should be careful not to exceed the maximum dose, as research shows that taking too much of any vitamin can lead to health problems.

Also, some medications can interact with vitamin supplements. Overall, it is important to speak with a healthcare provider before trying any supplement.

Various supplements are available for purchase online.

When is the best time to take supplements?

Vitamins are essential nutrients that mainly come from foods. Each performs various roles in the body, and deficiencies of different vitamins can harm health in different ways.

Aim to get vitamins from a balanced, varied diet that contains plenty of fruits and vegetables. If a person is pregnant or has a health issue or a restricted diet, a doctor or nutritionist may recommend supplements.