Vitamins
As with the minerals discussed above, some vitamins are recognized as essential nutrients, necessary in the diet for good health. (Vitamin D is the exception: it can be synthesized in the skin, in the presence of UVB radiation). Certain vitamin like compounds that are recommended in the diet, such as carnitine, are thought useful for survival and health, but these are not “essential” dietary nutrients because the human body has some capacity to produce them from other compounds.
Moreover, thousands of different phytochemicals have recently been discovered in food (particularly in fresh vegetables), which may have desirable properties including antioxidant activity, however, experimental demonstration has been suggestive but inconclusive. Other essential nutrients that are not classified as vitamins include essential amino acids, choline, essential fatty acids, and the mineral discussed in the preceding section.
Vitamin deficiencies may result in disease conditions, including goitre, scurvy, osteoporosis, impaired immune system, disorders of cell metabolism, certain forms of cancer, symptoms of premature aging and poor psychological health (including eating disorders), among many others.
Excess levels of some vitamins are also dangerous to health (notable vitamin A) and for at least one vitamin, B6, toxicity begins at levels not far above the required amount. Deficient or excess levels of minerals can also have serious health consequences.
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