Why do we need vitamin A?
Vitamin A is part of a group of compounds known as retinoids. Vitamin A promotes good eyesight and helps keep the skin and mucous membranes resistant to infection. Vitamin A also enhances immunity, enabling the body to defend against colds, influenza, many infections, and certain cancers, and prevents certain skin disorders.
What are some good sources of vitamin A?
Vitamin A can be found in a number of common foods, including fish liver oils, egg yolks, butter and cream, and dark green and yellow fruits and vegetables (especially carrots, asparagus, apricots, spinach, yellow squash, and sweet potatoes).
What can happen if we don't get enough vitamin A?
Night blindness, dry hair and skin, insomnia, fatigue, frequent colds and other respiratory infections, skin disorders (such as acne) and weight loss have been attributed to vitamin A deficiencies. Children are most at risk of vitamin A deficiency because they have not yet developed adequate vitamin A stores.

Vitamin B1 (Thiamin)

What is vitamin B1?
Also known as thiamin, vitamin B1 is a water-soluble vitamin. Since it is not stored in body fat, after the body uses what it needs, any excess vitamin B1 is excreted in the urine.
Why do we need it?
Like most of the B vitamins, thiamin plays a variety of roles in the human body. Its most important function is to help the body's cells convert carbohydrates into ATP – the fuel the body runs on. It is also involved in metabolic activities relating to the heart, brain and muscles, and it helps ensure proper nerve cell function.
How much vitamin B1 should I take?
According to the National Academy of Science, the recommended daily allowance (RDA) for thiamin is as follows:

• Adult men: 1.5 milligrams/day
• Adult women: 1.1 milligrams/day
• Children aged 7-10: 1 milligram/day
• Infants: 0.4 milligrams/day
• Pregnant/lactating women: 1.6 milligrams/day

What are some good sources of vitamin B1?
Thiamin is found in almost all foods, but the best sources are pork and other lean meats. Other good sources include enriched and fortified cereals, oatmeal, corn, nuts, beans, cauliflower and sunflower seeds.
What can happen if I don't get enough vitamin B1?
Vitamin B1 deficiency can result in edema and abnormal heart rhythm. Severe B1 deficiency (also known as beriberi) is rare in the U.S. but can occur in severely malnourished people, alcoholics, or people on long-term dialysis. Symptoms may include paralysis, loss of balance, loss of feeling in the legs and feet, visual problems and congestive heart failure.
What can happen if I take too much?
To date, no toxic effects have been reported for vitamin B1. Because it is water-soluble and is not stored in the body, the chances of enough B1 building up to toxic levels are highly unlikely. Most people taking multivitamins with high levels of B1 or eating foods rich in amounts of B1 need not worry about toxicity.

Vitamin B2 (Riboflavin)

What is vitamin B2?
Also known as riboflavin, vitamin B2 is a water-soluble vitamin. Since it is not stored in body fat, after the body uses what it needs, any excess vitamin B2 is excreted in urine or sweat.
Why do we need it?
Vitamin B2 works with the other B vitamins in maintaining body growth and the production of red blood cells. Like thiamin, it helps metabolize carbohydrates into energy. Some studies have shown that vitamin B2 may protect against cataracts, migraine headaches and sickle cell anemia.
How much vitamin B2 should I take?
According to the National Academy of Sciences, the recommended daily allowance (RDA) for riboflavin is as follows:

• Adult men: 1.7 milligrams/day
• Adult women: 1.3 milligrams/day
• Children aged 7-10: 1.2 milligrams/day
• Infants: 0.5 milligrams/day
• Pregnant/lactating women: 1.8 milligrams/day

What are some good sources of vitamin B2?
Large amounts of riboflavin can be found in lean meats, fortified cereals and yogurt. Other good sources include milk, cheese, eggs, broccoli and spinach. Because riboflavin is destroyed by exposure to light, foods that contain riboflavin should not be stored in glass containers that are exposed to light.
What can happen if I don't get enough vitamin B2?
Because riboflavin is so plentiful in the average diet, deficiencies are quite uncommon. However, people who do not get enough riboflavin can suffer from dry or cracked skin, especially around the lips or corners of the mouth. Other symptoms include skin rashes and eye irritation. Severe deficiencies may lead to depression or hysteria.
What can happen if I take too much?
Excess consumption of riboflavin may cause a person's urine to become bright yellow, but to date, no toxic side-effects have been reported. Because it is water-soluble and is not stored in the body, the chances of enough riboflavin building up to toxic levels are highly unlikely. Most people taking multivitamins with high levels of riboflavin or eating foods rich in riboflavin need not worry about toxicity.

Vitamin B3 (Niacin)

What is niacin?
Niacin, a white crystalline substance, belongs to the B-vitamin group. A water-soluble vitamin, it is absorbed in the intestines and carried throughout the body in the bloodstream. After the body uses what it needs, any excess niacin is excreted in urine.
Why do we need it?
Niacin helps break down blood sugar for energy. It also acts as a vasodilator, widening blood vessels and helping increase blood flow. Some health experts have prescribed niacin supplements for helping people lower high cholesterol or triglyceride levels; it thus plays a major role in protecting against cardiovascular disease.
How much niacin should I take?
According to the National Academy of Sciences, the recommended daily allowance (RDA) for niacin is as follows:

• Adult men: 19 milligrams/day
• Adult women: 15 milligrams/day
• Children aged 7-10: 13 milligrams/day
• Infants: 6 milligrams/day
• Pregnant/lactating women: 19 milligrams/day.

What are some good sources of niacin?
One of the best sources of niacin is fish, particularly mackerel and swordfish. Niacin can also be found in chicken, veal, pork, salmon, milk, eggs, fortified cereals, avocados, and some nuts.
What can happen if I don't get enough niacin?
Niacin deficiency causes pellagra, a chronic disease characterized by skin eruptions, digestive and nervous disturbances and mental deterioration. The condition can usually be reversed by taking niacin supplements.
Anemia may also occur as a result of low niacin levels, although this is usually due to an accompanying deficiency in folic acid.
What can happen if I take too much?
Niacin toxicity can lead to a variety of conditions. Even mildly high doses can cause a dilation of the blood vessels and lead to a potentially painfully tingling about the face and shoulders called the "niacin flush," as well as headaches, itchiness and stomach problems. Larger doses may cause diarrhea, nausea, ulcers, gout, diabetes and in rare cases, liver damage. Most of these conditions (with the exception of liver damage) can usually be reversed by discontinuation of high doses.

Vitamin B6 (Pyridoxine)

What is vitamin B6?
Also known as pyridoxine, vitamin B6 is a water-soluble vitamin absorbed by the intestines and carried throughout the body in the bloodstream. Since it is not stored in body fat, after the body uses what it needs, any excess vitamin B6 is excreted in urine or sweat.
Why do we need it?
Vitamin B6 is considered the "master vitamin" in the processing of amino acids. It helps build up and break down amino acids and is needed to make serotonin, melatonin and dopamine. It also aids in the production of red and white blood cells, converts a substance called tryptothan to niacin, and plays a role in the metabolism of proteins and fats. Large doses of B6 may reduce the symptoms of premenstrual syndrome, carpal tunnel syndrome and depression.
How much vitamin B6 should I take?
According to the National Academy of Sciences, the recommended daily allowance (RDA) for pyridoxine is as follows:

• Adult men: 2 milligrams/day
• Adult women: 1.6 milligrams/day
• Children aged 7-10: 1.4 milligrams/day
• Infants: 0.6 milligrams/day
• Pregnant/lactating women: 2.2 milligrams/day

What are some good sources of vitamin B6?
The best sources of pyridoxine include meats, oily fish (especially tuna), poultry, legumes and leafy green vegetables. Other good sources include potatoes (with skins), avocados, watermelon, bananas, carrots, brewer's yeast and fortified cereals.
What can happen if I don't get enough vitamin B6?
Vitamin B6 deficiency is rare. However, alcohol and tobacco have been shown to impair the absorption of B6, as have a number of drugs, including ethionamide, hyrdalazine and penicillamine.
B6 deficiency can cause skin problems and nervous system disorders, including impaired memory and concentration. A lack of B6 has also been associated with increased levels of the chemical homocysteine, which in turn has been associated with heart disease, birth defects, Alzheimer's disease and possibly dementia. Increasing one's intake of fruits and vegetables may reduce homocysteine levels.
What can happen if I take too much?
Taking very high doses (>2,000 mg per day) of pyridoxine for months or years can cause numbness in the feet and hands, which may be permanent in some cases. Supplementation should be stopped immediately if any of these symptoms begin to develop. Pyridoxine also reduces the effects of L-dopa, a drug used to treat Parkinson's disease.

Vitamin B12

What is vitamin B12?
Discovered in 1948, vitamin B12 is a water-soluble vitamin absorbed in the intestines and carried throughout the body in the bloodstream. Since it is not stored in body fat, after the body uses what it needs, any excess B12 is excreted via urine or sweat.
Why do we need it?
Vitamin B12 is essential for the production of red blood cells. It plays a role in the metabolization of proteins and fats and the synthesis of myelin, a fatty substance that encases nerve fibers. Vitamin B12 also displays some antioxidant properties. It works with folate to convert the amino acid homocysteine into methionine, a substance that helps prevent cells from becoming malignant.
Vitamin B12 injections have also been rumored to increase energy, although at present, there has been no scientific evidence to substantiate this claim.
How much vitamin B12 should I take?
According to the National Academy of Sciences, the recommended daily allowance (RDA) for vitamin B12 is as follows:

• Adult men: 2-2.4 micrograms/day
• Adult women: 2-2.4 micrograms/day
• Children aged 7-10: 1.4 micrograms/day
• Infants: 0.5 micrograms/day
• Pregnant/lactating women: 2.6 micrograms/day

What are some good sources of vitamin B12?
The only natural dietary sources of vitamin B12 come from animal products such as meats, eggs, milk, cheese, yogurt and fish. Clams and oily fish such as tuna, cod and sardines are particularly high in B12. Most fortified cereals also contain high quantities of vitamin B12.
What can happen if I don't get enough vitamin B12?
While B12 deficiency is rare in young people, the elderly may have trouble absorbing natural vitamin B12 and require supplements. Symptoms of B12 deficiency can include memory loss, instability, disorientation, nerve damage, decreased reflexes and possible hearing loss. A lack of B12 has also been linked with increased levels of homocysteine, which in turn has been associated with heart disease, birth defects and Alzheimer's disease.
B12 deficiency may also be caused by a genetic defect, in which a protein known as gastric intrinsic factor is not present in the body. In such cases, a condition known as pernicious anemia can develop. The condition must be treated with B12 injections, or neurologic damage may occur.
What can happen if I take too much?
To date, no reports of toxicity have been associated with high intake levels of vitamin B12. Because it is water-soluble and is not stored in the body, the chances of enough B12 building up to toxic levels are extremely unlikely.

Vitamin C

Why do we need vitamin C?
Vitamin C is one of several antioxidants shown to play a key role in the prevention of many types of cancers. Vitamin C maintains collagen, a protein necessary for the formation of skin, ligaments and bones. It also enhances the immune system, helps heal wounds and mend fractures, and aids in resisting some types of bacterial and viral infections.
What are some good sources of vitamin C?
Citrus fruits (oranges, grapefruit, lemons, mangos, etc.) are great sources of vitamin C, as are many green vegetables (especially asparagus, broccoli, spinach, green peppers, and peas). Other good sources of vitamin C include tomatoes, potatoes and cabbage.
What can happen if we don't get enough vitamin C?
Scurvy (hemorrhages), loose teeth, gingivitis (bad breath), bone disease, bleeding gums, increased chance for infection, colds or respiratory infections can be unpleasant consequences of vitamin C deficiency.

Vitamin D

What is vitamin D?
Vitamin D is actually a term for a group of hormones that are stored mainly in the liver, as well as fat and muscle tissue. It is one of three vitamins naturally manufactured by the body, and it is produced by a chemical reaction to the ultraviolet radiation contained in sunlight.
Why do we need it?
Vitamin D increases the body's absorption and metabolism of calcium and phosphorus. This makes it essential to maintaining strong, healthy bones and teeth.
How much vitamin D should I take?
According to the National Academy of Sciences, the recommended daily allowance (RDA) for vitamin D is as follows:

• Adult men: 200 international units (5 micrograms)/day
• Adult women: 200 international units (5 micrograms)/day
• Adults age 51-70: 400 international units (10 micrograms)/day
• Adults 71 and over: 600 international units (15 micrograms)/day
• Children aged 7-10: 200 international units (5 micrograms)/day
• Infants: 200 international units (5 micrograms)/day
• Pregnant/lactating women: 200 international units (5 micrograms)/day

What are some good sources of vitamin D?
Exposure to sunlight is the easiest way to build up stores of vitamin D. By exposing the face, hands and forearms for between 15-20 minutes two or three times per week, most people can manufacture all the vitamin D they need.
Vitamin D is also found in a number of food products, most notably vitamin D-fortified milk. Other sources include egg yolks, fish, cheese, fortified cereals and liver.
What can happen if I don't get enough vitamin D?
Vitamin D deficiency can result in bone-related disorders such as rickets in children and osteomalacia in adults. Vitamin D deficiency also increases the risk of hip fractures in postmenopausal women, and has been linked to higher incidences of prostate cancer and breast cancer.
What can happen if I take too much vitamin D?
High doses of vitamin D can be very toxic. In children, large doses can cause mental retardation, stunted growth and kidney failure. In older children and adults, too much vitamin D can result in weakness, anorexia, nausea, diarrhea and changes in a person's mental state. With the exception of kidney failure, low-calcium diets and withdrawal of vitamin D from a person's diet can usually reverse these side-effects.

Vitamin E

What is vitamin E?
Also known as tocopherol or alpha-tocopherol, vitamin E is a fat-soluble vitamin stored in the liver. It is one of three vitamins which also act as antioxidants.
Why do we need it?
In its role as an antioxidant, vitamin E helps neutralize unstable particles called free radicals which damage cell membranes. It also inhibits the oxidation of LDL cholesterol ("bad" cholesterol), which may reduce the risk of arterial plaque buildup, stroke and heart attacks. In addition, vitamin E plays an important function in the formation of red blood cells and the use of vitamin K. Some studies have shown that vitamin E may raise one's resistance to infectious diseases and protect against cataracts.
How much vitamin E should I take?
According to the National Academy of Sciences, the recommended daily allowance for vitamin E (alpho-tocopherol) is as follows:

• Adult men: 10 milligrams/day
• Adult women: 8 milligrams/day
• Children aged 7-10: 7 milligrams/day
• Infants: 4 milligrams/day
• Pregnant/lactating women: 12 milligrams/day

In addition to the NAS guidelines, some groups recommend much higher doses (between 70-130 milligrams/day).
What are some good sources of vitamin E?
Vitamin E is found in vegetable oils (most notably wheat germ oil), sweet potatoes, avocados, nuts, sunflower seeds and soybeans. Smaller amounts are found in egg yolks and green leafy vegetables.
What can happen if I don't get enough vitamin E?
Deficiencies of vitamin E have been linked to heart disease. People with extremely low blood levels of vitamin E may be also be at higher risk for cancer.
What can happen if I take too much?
Some people taking massive amounts of vitamin E have reported experiencing fatigue, nausea and diarrhea. Too much vitamin E may also cause bleeding problems, particularly in people taking anti-clotting medications.

Vitamin K