Vitamins are organic substances that are essential for the human body owing to the role they play in certain vital physiological functions. There are 13 vitamins that, unlike vitamin D and vitamin K, cannot be produced by the body and must therefore be consumed regularly.

Vitamins are classified according to their solubility: while fat-soluble vitamins can be stored by the body, water-soluble vitamins are excreted mainly through the urine, meaning that a consistent daily intake of these vitamins is especially important. The fat-soluble vitamins include vitamin A, vitamin D, vitamin E and vitamin K. The water-soluble vitamins are vitamin C, vitamins B₁, B₂, B₆ and B₁₂, niacin, pantothenic acid (vitamin B₅), biotin (vitamin B₇) and folic acid.

A few vitamins can also be supplied in the form of their precursor (provitamin), which the body can then convert into the corresponding active form.