A prolonged intake of less than the minimum daily requirement of those vitamins and minerals which have been established as essential to human health will result in a wide variety of morbid physiological conditions known as "deficiency diseases".
Deficiency diseases may either be "clinical"—abnormal conditions which may be readily identified by those who are qualified — or "sub-clinical", where the signs and symptoms are not far enough advanced, or well enough defined to lend themselves to specific diagnosis of vitamin or mineral deficiencies.
The classical, clinical diseases such as frank scurvy, pellagra, beri-beri, are seldom found in the United States. Sub-clinical deficiency diseases, however, are not uncommon, and where the diet has been consistently lacking in one or more of these nutrients established as necessary to normal health, supplementation may be indicated.
Symptoms of deficiency conditions do not develop rapidly, but only after a prolonged period during which the daily intake of one or more of the essential nutrients has been consistently lower than the minimum daily requirement, or where there is an interference with the normal metabolic processes of absorption and utilization of a nutrient.
Symptoms of deficiency conditions may closely resemble those of other conditions caused by a variety of disturbances unrelated to malnutrition and, thus, they do not necessarily prove nutritional deficiencies.
The following vitamins and minerals have been established as essential to normal human health:
| *Vitamin A | *Vitamin C | *Calcium |
| *Vitamin B1 | *Vitamin D | *Phosphorus |
| *Vitamin B2 | *Iodine | *Iron |
| °Vitamin E | *Niacin or Niacinamide | |
| °Vitamin B6 | °Pantothenic Acid | °Potassium |
| °Vitamin B12 | °Copper | °Sodium |
| °Vitamin K | °Manganese | °Zinc |
| °Folic Acid | °Magnesium | °Linoleic Acid |
*Minimum daily requirements have been established
°Minimum daily requirements have not been established
The following vitamins and minerals have not been established as required in human health:
| Choline | Citrus Bioflavonoids | ParaAminobenzoic Acid |
| Inositol | Rutin | Fluorine |
| Biotin | Vitamin P | and others |
Scientific opinion is not lacking as to the efficacy of certain of the above nutrients, even though such evaluations may not be supported by a unanimity of scientific opinion, and there is disagreement concerning their significance in human nutrition.
However, it should be understood that all statements referring to them, herein, are made with the qualification that they have not been established as essential in human nutrition, and that there are differences of opinion as to their value in human health.