Nutritional Recommended Daily Allowances (RDAs) are broad enough to prevent vitamin deficiencies and avoid the side effects associated with large doses of some vitamins. If your diet doesn’t meet these nutrition guidelines, or if you take extreme amounts of vitamins as supplements, you may be in for trouble.
The good news is that vitamin deficiencies are rare among people who have access to a wide variety of foods and know how to put together a balanced diet. For example, the only people likely to experience a vitamin E deficiency are premature and/or low–birth weight infants and people with a metabolic disorder that keeps them from absorbing fat. A healthy adult may go as long as 10 years on a vitamin E–deficient diet without developing any signs of a problem.
Nutritionists use the term subclinical deficiency to describe a nutritional deficit not yet far enough advanced to produce obvious symptoms. In lay terms, however, the phrase has become a handy explanation for common but hard-to-pin-down symptoms, such as fatigue, irritability, nervousness, emotional depression, allergies, and insomnia. And it’s a dandy way to increase the sale of nutritional supplements.
Simply put, the RDAs protect you against deficiency. If your odd symptoms linger even after you take reasonable amounts of vitamin supplements, probably something other than a lack of any one vitamin is to blame. The following table lists the symptoms of various vitamin deficiencies.
| A Diet Low in This Vitamin | May Produce These Signs of Deficiency |
|---|---|
| Vitamin A | Poor night vision; dry, rough, or cracked skin; dry mucous membranes including the inside of the eye; slow wound healing; nerve damage; reduced ability to taste, hear, and smell; inability to perspire; reduced resistance to respiratory infections |
| Vitamin D | In children: rickets (weak muscles, delayed tooth development,
and soft bones, all caused by the inability to absorb minerals
without vitamin D) In adults: osteomalacia (soft, porous bones that fracture easily) |
| Vitamin E | Inability to absorb fat |
| Vitamin K | Blood fails to clot |
| Vitamin C | Scurvy (bleeding gums; tooth loss; nosebleeds; bruising; painful or swollen joints; shortness of breath; increased susceptibility to infection; slow wound healing; muscle pains; skin rashes) |
| Thiamin (vitamin B1) | Poor appetite; unintended weight loss; upset stomach; gastric upset (nausea, vomiting); mental depression; an inability to concentrate |
| Riboflavin (vitamin B2) | Inflamed mucous membranes, including cracked lips, sore tongue and mouth, burning eyes; skin rashes; anemia |
| Niacin | Pellagra (diarrhea; inflamed skin and mucous membranes; mental confusion and/or dementia) |
| Vitamin B6 | Anemia; convulsions similar to epileptic seizures; skin rashes; upset stomach; nerve damage (in infants) |
| Folate | Anemia (immature red blood cells) |
| Vitamin B12 | Pernicious anemia (destruction of red blood cells, nerve damage, increased risk of stomach cancer attributed to damaged stomach tissue, neurological/psychiatric symptoms attributed to nerve cell damage) |
| Biotin | Loss of appetite; upset stomach; pale, dry, scaly skin; hair loss; emotional depression; skin rashes (in infants younger than 6 months) |