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 vitaminsHere 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.
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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 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 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.
Here are the different types of vitamins.
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.
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.