Vitamins are organic compounds that the human body cannot produce and must therefore be consumed. Depending on how the intestines absorb them, vitamins are divided into fat-soluble (A, D, E, K) and water-soluble (all others). Vitamins are required in relatively small amounts because they are not used as building blocks or as sources of energy but rather as recyclable tools that maintain bodily functions. For example, folic acid (one of the water-soluble vitamins) acts as an aid in manufacturing some proteins. It is not used up, and, in fact, can be reused. Vitamin deficiencies are relatively rare in today’s society. When they do occur, the symptoms are generally mild and reversible. However, vitamin excess can occur and is becoming more of a problem since nutrition supplements are so readily available.


Several factors influence the amount of vitamins a person needs to consume. One’s need for certain vitamins varies by age. Infants, children, and pregnant- or breast-feeding women require more of some vitamins and minerals than do most adults. Furthermore, for a number of reasons, elderly people seem to be more prone to deficiencies of some vitamins. One reason is that the aging body is less able to absorb vitamins. Likewise, due to decreased sun exposure-which is required by the human skin to produce the active form of vitamin D-vitamin D deficiency also occurs in the elderly or institutionalized people.

Vitamin deficiencies can occur as the result of several factors, including the following:
  • a decreased dietary intake
  • a decreased absorption of vitamins in the intestines
  • the inability to "recycle" the vitamin
  • an increased need for a particular vitamin, such as in some disease states
Medication can also affect one’s need for certain vitamins. For example, Coumadin (a blood thinner used to prevent blood clots) directly affects the ability of vitamin K function in blood clotting. Other medications decrease absorption or increase the need of some vitamins. Similarly, a person’s habits can have a significant influence on vitamin needs. For instance, smoking affects blood levels of folic acid, beta-carotene, and vitamins C and E. Alcoholics are prone to thiamine (vitamin B1) deficiency, which can lead to permanent nerve-, brain-, and heart damage.

Dietary requirements

For most people, a well-balanced diet will provide all the needed vitamins. The specific amount of each vitamin can vary significant depending on a person’s age, gender, and medical conditions. For example, an infant requires 375 micrograms of Vitamin A daily, whereas a breastfeeding woman requires 1,200 micrograms, and an otherwise healthy adult male requires 1,000 micrograms. The current recommended daily allowance (RDA) of vitamins is based on the need to prevent deficiency states, but we now know that some vitamins can be beneficial in much higher doses. Niacin, for example, can be used to lower cholesterol, and to prevent some spinal cord development problems in their newborns, and women who want to become pregnant might benefit from higher doses of folic acid. Likewise, high-dose folic acid is also being evaluated to treat elevated levels of homocysteine, a compound that has been shown to lead to clotting problems and early heart disease. What we currently believe to be the right dose of a vitamin is subject to change as we learn more about that vitamin’s role in health. Unfortunately, taking large quantities of all vitamins can be very dangerous and can lead to toxicity. People need to avoid vitamin deficiencies but also realize that more is not always better.

The following paragraphs address specific vitamins, their dietary sources, the daily requirements for adults, and results of deficiencies and toxicities (excessive amount of vitamins.) Similar information for essential minerals can be found in a related article on "Essential Nutrients."

Vitamin A

Sources: Butter, milk, eggs, liver, some fish, green leafy vegetables, and colorful fruits and vegetables (carrots, tomatoes, sweet potatoes)
Daily requirements: 800 - 1000 micrograms
Results of Deficiency: Blindness, dry eyes, susceptibility to infections
Results of Toxicity:
Acute: increased pressure on brain, skin loss, liver failure
Chronic: hair loss, high cholesterol, balance problems, rash, mouth sores, liver failure, birth defects during pregnancy.

Thiamine (B1)

Sources: Pork, cereals (wheat, corn, rye), legumes, green vegetables, meat, fruits, milk
Daily requirements: ~ 1.5 milligrams
Results of Deficiency: (Common in Alcoholics, Asians, dialysis patients, and those on high carbohydrate diet) Causes nerve damage, dementia, heart failure; sometimes irreversible.
Results of Toxicity: Rare; intake of >400mg/day; lethargy, balance problems, intestinal problems.

Riboflavin (B2)

Sources: Milk, milk products, green vegetables, meat, liver, fish
Daily requirements: ~1.5 - 2.0 milligrams
Results of Deficiency: (Deficiency is very Rare) Swelling of lining of mouth and nose, mouth and lip sores, inflammation of tongue, dermatitis, anemia.
Results of Toxicity: None known

Niacin (B3)

Sources: Meat, liver, legumes, cereals, peanuts
Daily requirements: 15 - 20 milligrams (higher doses help lower cholesterol)
Results of Deficiency: (Common in China, Africa, and India) Classically known as pellagra: diarrhea, dementia, dermatitis; inflammation of mouth, tongue, and vagina; nerve pain
Results of Toxicity: Flushing (can be side effect of treatment doses for high cholesterol), high blood sugar, liver damage, high uric acid (which can cause gout)

Pyridoxine (B6)

Sources: Cereals, milk, meat, some vegetables.
Daily requirements: ~ 2.0 milligrams
Results of Deficiency: Inflammation of mouth, lips, and tongue; anxiety, depression, and confusion; anemia; rarely seizures; some medications can cause deficiency (isoniazid, alcohol, penicillamine, theophylline)
Results of Toxicity: > 200 mg/day can lead to nerve damage and sensitivity to light

Vitamin B12

Sources: Meat, liver, kidney, dairy products
Daily requirements: ~ 2.0 micrograms
Results of Deficiency: (Usually results from inability to absorb the vitamin due to diseases, including pernicious anemia or inadequate pancreatic function) Causes macrocytic anemia, nerve damage, and dementia
Results of Toxicity: None known

Ascorbic Acid (C)

Sources: Citrus fruits, juices, tomatoes, other fruits and vegetables
Dietary requirements: ~ 60 milligrams
Results of Deficiency: Called Scurvy; causes fatigue, depression, easy bruising and bleeding, weakened cartilage, coiled hairs, difficulty healing, thickened skin, abnormal bone growth in infants
Results of Toxicity: > 500 mg/day can cause nausea and diarrhea, potential cause of kidney stones, withdrawal from high doses can lead to scurvy, even with "normal" intake

Vitamin D

Sources: Eggs, cheese, milk, butter, and fish liver oils.
Daily requirements: 5-10 micrograms (15 min sun exposure to hands and face twice a month)
Results of Deficiency: Rickets (crooked bones) in kids, osteomalacia (soft bones) in adults, weak bones leading to deformity, easy fractures; low calcium levels
Results of Toxicity: High calcium and phosphate levels leading to confusion, kidney damage, calcium deposits

Vitamin E

Sources: Widely available in variety of foods with the richest source being vegetable oils.
Daily requirements: 3-10 milligrams
Results of Deficiency: (Rare; occurs in premature infants and those who cannot absorb fat) Causes sterility; and in infants anemia, nerve, eye and balance problems that may be permanent
Results of Toxicity: Extremely rare

Vitamin K

Sources: Made by bacteria inside the human intestines
Daily requirements: 50 - 80 micrograms
Deficiency: (Rare) hemorrhage, especially in newborn infants (they routinely receive vitamin K shots shortly after birth)
Toxicity: Rare; results in destruction of red blood cells and possibly brain damage in infants if they receive too much of it

Folic Acid (folate)

Sources: Kidney, liver, vegetables, meats, cereals, fruits, some dark green vegetables
Dietary requirements: 200 micrograms, higher doses in some situations
Results of Deficiency: Macrocytic (large red blood cells) anemia, inflammation of tongue, diarrhea; some drugs (sulfasalazine and phenytoin) can lead to deficiency.
Results of Toxicity: Can mask vitamin B12 deficiency; may increase risk of seizures in some people


Sources: Made by intestinal bacteria, available in many food sources
Daily requirements: 100-300 micrograms
Results of Deficiency: (Rare) Confusion, muscle pain, dermatitis, hair loss
Results of Toxicity: None reported

Pantothenic Acid

Sources: Widely available in many different food sources.
Daily requirements: 4 - 7 milligrams
Results of Deficiency: (Rare) Abdominal pain, vomiting, insomnia.
Results of Toxicity: > 10 gram/ day can cause diarrhea

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