Vitamin is a term used to describe the range of organic compounds an organism produces in insufficient quantities (if at all), yet still requires for important functions in its body.

To acquire these essential micronutrients, the organism must scavenge them from appropriate food sources. Since organisms make these 'vital' molecules in varying amounts, a much-needed nutrient for one living thing won't be scarce enough to be considered a vitamin in another. For example, dogs synthesize their own vitamin C (in their livers), but fish, birds, guinea pigs, and humans cannot.

These chemicals carry out a wide variety of tasks to help an organism grow, reproduce, or simply survive. Some act as signals, regulating metabolism of other materials. Others help enzymes work either directly as a cofactor, or indirectly in the production of one.

Who discovered the first vitamins?

There was no single discovery that established the category of nutrients we now call vitamins. By the late 19th century, chemistry and biology had combined to provide a series of insights into the complexity of human nutrition.

Scientists were realizing there had to be more to a healthy diet than the right balance of proteins, carbohydrates, fats, and minerals. Various studies on animal growth and development, many involving the modification of milk, pointed to the existence of factors essential for life that were present in extremely small concentrations.

In 1901, Dutch scientist Gerrit Grijns speculated that a nutrient deficiency could be responsible for outbreaks of a devastating disease called beri-beri in Indonesia. Further writing by his colleague, Christian Eijkman, inspired a Polish biochemist with undoubtedly one of the coolest names in science, Kazimierz Funk, to dig deeper, uncovering a specific kind of nitrogen compound (called an amine) that he maintained could prevent the illness.

Dubbed a 'vital amine', Funk's discovery of vitamin B3, or niacin, gave us both the term vitamin and the first clear link between absence of an organic essential micronutrient and a disease.

Though technically a deficiency in the closely related vitamin B1 (thymine) is what's responsible for beri-beri, the finding sparked a series of findings associating various compounds with important bodily functions.

What are some examples of vitamins?

For humans, there are just over a dozen compounds that are currently considered to be vitamins. Some are more easily soluble in fat, others in water, and can be found in select sources of meats, greens, nuts, and fungi. Here are some of the most common examples you may have taken in the past:

Vitamin A covers a small group of closely related compounds involved in regulating growth and development of cells throughout our body. Most active forms are retinol, retinal, and retinoic acid, with deficiencies having severe impacts on fetal development, immunity, and vision. Preformed vitamin A, or retinol, can be absorbed in the form of carotenoids in fruit and vegetables.

Vitamin B, or B complex vitamins, is a family of eight essential nutrients: thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9), and cobalamin (B12). Their functions are closely related, activating enzymes that build up or break down other materials involved in things like DNA repair, energy production, and signaling molecules in the brain. Most can't be stored in the body, which means a healthy diet in things like greens, fish, eggs, and organ meats.

Vitamin C, or ascorbic acid, has a variety of roles in our body, from helping us absorb iron to wound repair, to removing reactive oxidative species. Since we can't retain large stores of the compound, it depletes quickly and needs to be replenished with a healthy diet of fruits and vegetables. Historically, its absence in fresh greens on long voyages has been linked with the disease scurvy - a condition eventually fixed with provision of longer-lasting citrus fruits and pickled cabbage. However, it is becoming increasingly common again in some of the world's richest countries.

Why are vitamins named after letters?

In 1916, a paper by US biochemists Cornelia Kennedy and Elmer V. McCollum used the letters A and B to describe fat and water soluble organic compounds considered as vital accessory factors in nutrition. The system was soon expanded to include other vitamins discovered in ensuing years, with vitamin B split into two forms following the discovery of riboflavin in the early 1920s as a component of the original compound.

What is vitamin K?

Over time, vitamins designated letters F, G (now riboflavin) and H, have been relabelled, while the letter in vitamin K stands for the Danish spelling of coagulation, named so because of its involvement in this process. For this reason, vitamin K injections are given to newborns immediately after birth in many countries, to aid with blood clotting.

How many vitamins should I take?

While vitamins are important to health, most of us easily get the levels we need with a modern, balanced diet. Many studies have shown no long-term benefit in taking daily multivitamin tablets. In fact, there's evidence it can be better to get vitamins from your food if possible.

Do I need to take a daily multivitamin?

Unless a doctor has diagnosed that you have a deficiency in a particular vitamin, it's unlikely that you need to take daily supplements for long periods of time.

Can you take too many vitamins?

On top of that, it is possible to make yourself unwell from taking too many vitamins. Even water soluble vitamins such as vitamin C and vitamin B (which doesn't stay in the body) can cause symptoms such as diarrhea or heartburn if you take too much.

Other vitamins, such as vitamin A, have been linked to birth defects if taken to excess while a woman is pregnant.

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