A vitamin is an organic compound that is generally required in small amounts as a nutrient is most organisms. These compounds are called vitamins when they are unable to be synthesized in a sufficient quantity by an organism, and therefore must be obtained from an external source. The dependency that an organism has with a vitamin is completely dependent on what organism is being dealt with. An example of this would be ascorbic acid, that functions as vitamin C. This is for some animals, but not for other animals. Another is vitamins D and K, which are required in the diet of humans, under certain circumstances.

Deficiencies of vitamins are generally classified as primary, or secondary deficiencies. Primary deficiencies are when an organism is not provided enough of the specific vitamin within what is ingested. Secondary deficiencies can be attributed by outside influence(s) that affects the organisms ability to absorb vitamins. Examples of an “outside influence” are actions taken such as smoking, alcohol, or even medications that affect the body and can interfere with it’s absorption of vitamins. People who have diets that have variation are least likely to develop some form of deficiency, people who eat restricted diets can eventually develop deficiencies that cause painful – and even deadly diseases.

Human bodies are incapable of storing most essential vitamins, so it is necessary to ingest them often to avoid any form of deficiency. Vitamins, such as A, D, and B12, are stored in the liver, allowing most humans to go without these vitamins for months at a time before developing any form of deficiency. Other vitamins, such as vitamin B3 isn’t stored in large amounts within the body, so a diet lacking this vitamin will develop a deficiency in just a few weeks.

Human vitamin deficiencies that have developed well-known names include Beriberi, (or a Thiamine deficiency), Pellagra, (a Niacin deficiency), Scurvy, (a vitamin C deficiency), and Rickets, (which is caused by a vitamin D deficiency). Much of the world considers it to be, nowadays, rare to develop a deficiency. This can be attributed to easier and adequate sources of food, along with our implantation of essential vitamins in everyday foods.

Side effects can occur if too much of a specific vitamin is ingested, and varies in severity in respect to the size of the dosage ingested. Although an overdose of a vitamin is relatively uncommon, it can however occur. A large enough dosage can develop side effects such as diarrhea, nausea, and vomiting.

The simplest way to eliminate these symptoms, if they occur, is to reduce the current dosage. The amount it takes to cause a vitamin excess to occur varies from individuals, in direct relation to your health conditions, and your age. Most vitamin overdoses in the U.S occur in young children.