This is because the human body either does not produce enough of them, or it does not produce any at all.
Each organism has different vitamin requirements. For example, humans need to consume vitamin C, or ascorbic acid, but dogs do not. Dogs can produce, or synthesize, enough vitamin C for their own needs, but humans cannot.
People need to get most of their vitamin D from exposure to sunlight, because it is not available in large enough quantities in food. However, the human body can synthesize it when exposed to sunlight.
Different vitamins have different roles, and they are needed in different quantities.
This article explains what vitamins are, what they do, and which foods provide each type. Follow the links for more information about each type of vitamin.
Fast facts on vitamins
Here are some key points about vitamins. More detail and supporting information is in the main article.
- There are 13 known vitamins.
- Vitamins are either water-soluble or fat-soluble.
- Fat-soluble vitamins are easier for the body to store than water-soluble.
- Vitamins always contain carbon, so they are described as "organic."
- Food is the best source of vitamins, but some people may be advised by a physician to use supplements.
What are vitamins?
Fruits and vegetables are good sources of a range of vitamins.
A vitamin is one of a group of organic substances that is present in minute amounts in natural foodstuffs. Vitamins are essential to normal metabolism. If we do not take enough of any kind of vitamin, certain medical conditions can result.
A vitamin is both:
- an organic compound, which means it contains carbon
- an essential nutrient that body cannot produce enough of and which it needs to get from food
There are currently 13 recognized vitamins.
Fat-soluble and water-soluble vitamins
Vitamins are either fat-soluble or water-soluble.
Fat-soluble vitamins
Fat-soluble vitamins are stored in the fatty tissues of the body and the liver. Vitamins A, D, E, and K are fat-soluble. These are easier to store than water-soluble vitamins, and they can stay in the body as reserves for days, and sometimes months.
Fat-soluble vitamins are absorbed through the intestinal tract with the help of fats, or lipids.
Water-soluble vitamins
Water-soluble vitamins do not stay in the body for long. The body cannot store them, and they are soon excreted in urine. Because of this, water-soluble vitamins need to be replaced more often than fat-soluble ones.
Vitamin C and all the B vitamins are water soluble.
Types
Here are the different types of vitamins.
Vitamin A
Chemical names: Retinol, retinal, and four carotenoids, including beta carotene.
- It is fat soluble.
- Deficiency may cause night-blindness and keratomalacia, an eye disorder that results in a dry cornea.
- Good sources include: Liver, cod liver oil, carrots, broccoli, sweet potato, butter, kale, spinach, pumpkin, collard greens, some cheeses, egg, apricot, cantaloupe melon, and milk.
Vitamin B
Chemical name: thiamine.
- It is water soluble.
- Deficiency may cause beriberi and Wernicke-Korsakoff syndrome.
- Good sources include: yeast, pork, cereal grains, sunflower seeds, brown rice, whole-grain rye, asparagus, kale, cauliflower, potatoes, oranges, liver, and eggs.
Vitamin B2
Chemical name: Riboflavin
- It is water soluble
- Deficiency may cause ariboflavinosis
- Good sources include: asparagus, bananas, persimmons, okra, chard, cottage cheese, milk, yogurt, meat, eggs, fish, and green beans
Vitamin B3
Chemical names: Niacin, niacinamide
- It is water soluble.
- Deficiency may cause pellagra, with symptoms of diarrhea, dermatitis, and mental disturbance.
- Good sources include: liver, heart, kidney, chicken, beef, fish (tuna, salmon), milk, eggs, avocados, dates, tomatoes, leafy vegetables, broccoli, carrots, sweet potatoes, asparagus, nuts, whole-grains, legumes, mushrooms, and brewer's yeast.
Vitamin B5
Chemical name: Pantothenic acid
- It is water soluble.
- Deficiency may cause paresthesia, or "pins and needles."
- Good sources include: meats, whole-grains (milling may remove it), broccoli, avocados, royal jelly, and fish ovaries.
Vitamin B6
Chemical names: Pyridoxine, pyridoxamine, pyridoxal
- It is water soluble.
- Deficiency may cause anemia, peripheral neuropathy, or damage to parts of the nervous system other than the brain and spinal cord.
- Good sources include: meats, bananas, whole-grains, vegetables, and nuts. When milk is dried, it loses about half of its B6. Freezing and canning can also reduce content.
Vitamin B7
Chemical name: Biotin
- it is water soluble.
- Deficiency may cause dermatitis or enteritis, or inflammation of the intestine.
- Good sources include: egg yolk, liver, some vegetables.
Vitamin B9
Chemical names: Folic acid, folinic acid
- It is water soluble.
- Deficiency during pregnancy is linked to birth defects. Pregnant women are encouraged to supplement folic acid for the entire year before becoming pregnant.
- Good sources include: leafy vegetables, legumes, liver, baker's yeast, some fortified grain products, and sunflower seeds. Several fruits have moderate amounts, as does beer.
Vitamin B12
Chemical names: Cyanocobalamin, hydroxocobalamin, methylcobalamin
- It is water soluble.
- Deficiency may cause megaloblastic anemia, a condition where bone marrow produces unusually large, abnormal, immature red blood cells.
- Good sources include: fish, shellfish, meat, poultry, eggs, milk and dairy products, some fortified cereals and soy products, as well as fortified nutritional yeast.
Vegans are advised to take B12 supplements.
Vitamin C
Chemical name: Ascorbic acid
- It is water soluble.
- Deficiency may cause megaloblastic anemia.
- Good sources include: fruit and vegetables. The Kakadu plum and the camu camu fruit have the highest vitamin C contents of all foods. Liver also has high levels. Cooking destroys vitamin C.
Vitamin D
Chemical names: Ergocalciferol, cholecalciferol.
- It is fat soluble.
- Deficiency may cause rickets and osteomalacia, or softening of the bones.
- Good sources: Exposure to ultraviolet B (UVB) through sunlight or other sources causes vitamin D to be produced in the skin. Also found in fatty fish, eggs, beef liver, and mushrooms.
Vitamin E
Chemical names: Tocopherols, tocotrienols
- It is fat soluble.
- Deficiency is uncommon, but it may cause hemolytic anemia in newborns. This is a condition where blood cells are destroyed and removed from the blood too early.
- Good sources include: Kiwi fruit, almonds, avocado, eggs, milk, nuts, leafy green vegetables, unheated vegetable oils, wheat germ, and whole-grains.
Vitamin K
Chemical names: Phylloquinone, menaquinones
- It is fat soluble.
- Deficiency may cause bleeding diathesis, an unusual susceptibility to bleeding.
- Good sources include: leafy green vegetables, avocado, kiwi fruit. Parsley contains a lot of vitamin K.
Dietary sources
The 2015-2020 U.S. Dietary Guidelines focus on the overall diet as the best way to get enough nutrients for good health. Vitamins should come firstly from a balanced and varied diet with plenty of fruit and vegetables.
However, in some cases, fortified foods and supplements may be appropriate.
A health professional may recommend vitamin supplements for people with certain conditions, during pregnancy, or for those on a restricted diet.
Those taking supplements should take care not to exceed the stated maximum dose, as health problems can result. Some medications can interact with vitamin supplements, too, so it is important to talk to a healthcare provider before using supplements.
Video: The ABCs of vitamins
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Vitamins: What are they and what do they do?
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