Photo courtesy NASA
Illustrated vitamin B12 molecule.
We've all stared at the cereal box label during breakfast and wondered what words like riboflavin, folic acid and pyridoxine mean. Has your mom ever reminded you to eat a balanced diet and "make sure you eat your greens"? The words on your cereal box and your mother's good advice both involve vitamin B. The B vitamins are a group of eight individual vitamins, often referred to as the B-complex vitamins. In this article, we will take a look at how the B vitamins work so you can begin to understand why Kellogg's and your mother made sure you included these essential vitamins in your diet. We'll also look at some of the more serious conditions that can result from B vitamin deficiencies.
The word vitamin is derived from a combination of words -- vital amine -- and was conceived by Polish chemist Casimir Funk in 1912. Funk isolated vitamin B1, or thiamine, from rice. This was determined to be one of the vitamins that prevented beriberi, a deficiency disease marked by inflammatory or degenerative changes of the nerves, digestive system and heart.
If you read What are vitamins and how do they work?, you know that vitamins are organic (carbon containing) molecules that mainly function as catalysts for reactions within the body. A catalyst is a substance that allows a chemical reaction to occur using less energy and less time than it would take under normal conditions. If these catalysts are missing, as in a vitamin deficiency, normal body functions can break down and render a person susceptible to disease.
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The body requires vitamins in tiny amounts (hundredths of a gram in many cases). We get vitamins from these three primary sources:
- Our bodies -- Vitamin K and some of the B vitamins are produced by bacteria within our intestines, and vitamin D is formed with the help of ultraviolet radiation, or sunshine, on the skin.
Vitamins are either fat-soluble or water-soluble. The fat-soluble vitamins can be remembered with the mnemonic (memory aid) ADEK, for the vitamins A, D, E and K. These vitamins accumulate within the fat stores of the body and within the liver. Fat-soluble vitamins, when taken in large amounts, can become toxic. Water-soluble vitamins include vitamin C and the B vitamins. Water-soluble vitamins taken in excess are excreted in the urine but are sometimes associated with toxicity. Both the B vitamins and vitamin C are also stored in the liver.
The B-complex vitamins are actually a group of eight vitamins, which include:
- thiamine (B1)
- riboflavin (B2)
- niacin (B3)
- pantothenic acid (B5)
- pyridoxine (B6)
- cyanocobalamin (B12)
- folic acid
These vitamins are essential for:
- The breakdown of carbohydrates into glucose (this provides energy for the body)
- The breakdown of fats and proteins (which aids the normal functioning of the nervous system)
- Muscle tone in the stomach and intestinal tract
Some doctors and nutritionists suggest taking the B-complex vitamins as a group for overall good health. However, most agree that the best way to get our B vitamins is naturally -- through the foods we eat!
Where B Vitamins Come From and Why They're Important
The B-complex vitamins are found in brewer's yeast, liver, whole-grain cereals, rice, nuts, milk, eggs, meats, fish, fruits, leafy green vegetables and many other foods. Keep reading for more specifics about each of the B vitamins:
The B vitamin thiamine is essential for the metabolism of carbohydrates into the simple sugar glucose. The chemical process involves the combination of thiamine with pyruvic acid to form a coenzyme, a substance that, when combined with other substances, forms an enzyme. Enzymes are those all-important proteins that speed up chemical reactions in the body. Thiamine is also important for the proper functioning of the nervous system. In this instance, thiamine acts as a coenzyme in the production of the neurotransmitter (chemical messenger between nerve fibers) acetylcholine.
Thiamine deficiency is rare but often occurs in alcoholics, because alcohol interferes with the absorption of thiamine through the intestines. There are several health problems associated with a deficiency of thiamine. The first is beriberi, a disease that is characterized by anemia, paralysis, muscular atrophy and weakness, and spasms in the muscles of the legs. Other disorders caused by thiamine deficiency include Wernicke's encephelopathy, which causes lack of coordination, and Korsakoff's psychosis, which affects short-term memory. The mouth can also be affected by thiamine deficiency, increasing the sensitivity of the teeth, cheeks and gums, as well as "cracks" in the lips. Fortunately, these conditions can be reversed with the addition of the vitamin.
Thiamine is found in whole-grain cereals, bread, red meat, egg yolks, green leafy vegetables, legumes, sweet corn, brown rice, berries, yeast, the germ and husks of grains and nuts. Mega-doses (very high doses) of thiamine have not been associated with adverse health effects, and excess of the water-soluble vitamin is excreted.
Riboflavin is important in the breakdown of carbohydrates, fats and proteins, and, like thiamine, it acts as a coenzyme in the process. It is also significant in the maintenance of the skin and mucous membranes, the cornea of the eye and for nerve sheaths. Riboflavin also acts as a coenzyme for oxidation-reduction reactions throughout the body. Oxidation reduction reactions involve the addition of either oxygen or hydrogen to a substance. One important consequence of this process is when it acts to inhibit chemical reactions with oxygen or highly reactive free radicals. These oxidation reactions can cause damage to our cells. (See How Cells Work.)
A deficiency of riboflavin can cause skin disorders (seborrheic dermatitis) and inflammation of the soft tissue lining around the mouth and nose, anemia, and can cause the eyes to be light-sensitive. In the mouth, angular cheilosis can develop. This is a painful condition where lesions develop at the corners of your lips, and glossitis (inflammation of the tongue) can also occur.
Riboflavin is found in whole-grain products, milk, meat, eggs, cheese and peas. As a water-soluble vitamin, any excess is excreted, although small amounts are stored in the liver and kidney.
Niacin, also known as nicotinic acid and nicotinamide, is needed for the metabolism of food, the maintenance of healthy skin, nerves and the gastrointestinal tract. Niacin is also used in those all-important oxidation reduction reactions. A deficiency of niacin causes the disease, pellagra. In the past, this disease was often associated with the very poor and was also a major cause of mental illness. The symptoms of pellagra are sometimes referred to as the "three D's" -- diarrhea, dermatitis and dementia -- ultimately resulting in a fourth "D", death. The mouth is also affected by pe llagra, which can cause the inside of the cheeks and tongue to become red and painful. Fortunately, high doses of niacin (150-300 mg.) can reverse the effects of this disease.
Niacin is found in protein-rich food such as meats, fish, brewer's yeast, milk, eggs, legumes, potatoes and peanuts. Niacin can also be prescribed in higher doses as a drug to help lower cholesterol (see How Cholesterol Works), but can cause side effects. The main side effects of high doses of niacin include flushing of the skin (due to dilating blood vessels), itching, headaches, cramps, nausea and skin eruptions.
Pyridoxine, also known as pyridoxal phosphate and pyridoxamine, is needed (like some of the other B vitamins) for the breakdown of carbohydrates, proteins and fats. Pyridoxine is also used in the production of red blood cells, as well as in the biochemical reactions involved in the metabolism of amino acids (the building blocks of protein). Due to the abundance of pyridoxine in many foods, a deficiency is rare except in alcoholics, where it is often present. A pyridoxine deficiency causes skin disorders (similar to symptoms brought on by riboflavin and niacin deficiencies), neuropathy (abnormal nervous system), confusion, poor coordination and insomnia. Oral signs of pyridoxine deficiency include inflammation of the edges of the lips, tongue and the rest of the mouth. High doses of pyridoxine are sometimes touted as a remedy for premenstrual syndrome (see How PMS Works), but research has not supported this assertion. Mega-doses of pyridoxine can cause nerve damage.
Pyridoxine is found in many foods, including liver, organ meats, brown rice, fish, butter, wheat germ, whole grain cereals, soybeans and many others.
Vitamin B12 is necessary for processing carbohydrates, proteins and fats and to help make all of the blood cells in our bodies. Vitamin B12 is also required for maintenance of our nerve sheaths. Vitamin B12 acts as a coenzyme in the synthesis and repair of DNA.
Vitamin B12 cannot be absorbed or used by the body until it is combined with a mucoprotein made in the stomach and called intrinsic factor. Once the B12 becomes bound to the intrinsic factor, it is able to pass into the small intestine to be absorbed and used by the body. Vitamin B12 deficiency is sometimes seen in strict vegetarians who do not take vitamin supplements, and those who have an inability to absorb the vitamin (usually from a failure to produce intrinsic factor). Although enough B12 is stored in the liver to sustain a person for many years, a deficiency will cause a disorder known as pernicious anemia. Pernicious anemia causes weakness, numbness of the extremities, pallor, fever and other symptoms. Mouth irritation and brain damage are also common consequences of B12 deficiency. However, these very serious effects can be reversed by vitamin B12 shots. Shots are needed because the deficiency is often caused by an inability to absorb the vitamin when taken orally. As we age, our stomachs have an increasingly difficult time producing intrinsic factor. Many doctors recommend that people over 60 have their vitamin B12 levels checked, to see if a B12 shot is needed.
Vitamin B12 is not found in any plant food sources and is produced almost solely by bacteria, such as streptomyces griseus. Rich sources of B12 include liver, meat, egg yolk, poultry and milk.
Folic acid (B9)
Photo courtesy USDA
Chemist Robert Jacob prepares blood samples for analysis in a study of folic acid.
Folic acid, also known as folacin and pteroylglutamic acid, is one of the B-complex vitamins that interacts with vitamin B12 for the synthesis of DNA, which is important for all cells in the body. Folic acid, in combination with vitamin B12 and vitamin C), is necessary for the breakdown of proteins and the formation of hemoglobin, a compound in red blood cells that transports oxygen and carbon dioxide. Folic acid is also essential to virtually all biochemical reactions that use a one-carbon transfer and is produced by bacteria in the stomach and intestines.
A deficiency of folic acid causes anemia, poor growth, and irritation of the mouth -- all of which are similar to symptoms suffered by those with B12 deficiency. Folic acid is present in nearly all natural foods but can be damaged, or weakened, during cooking. Deficiencies are found mainly in alcoholics, the malnourished, the poor, the elderly and those who are unable to absorb food due to certain diseases (topical sprue, gluten enteropathy).
Folic acid is found in yeast, liver, green vegetables, whole grain cereals and many other foods. The need for folic acid increases during pregnancy, due to high requirements of the vitamin from the fetus. Doctors often suggest a 300 mcg. daily supplement for pregnant women. Many nutritional requirements change during pregnancy, and vitamins are no exception. All of the B vitamins, especially folic acid, should be slightly increased during pregnancy and lactation (breast milk production). The daily intake of folic acid should be increased from 180 mcg. to 400 mcg. during pregnancy and from 180 mcg. to 280 mcg. during lactation. (Test Your Folic Acid Smarts with this quiz!)
Mega-doses of folic acid can produce convulsions, interfere with the anticonvulsant medication used by epileptics, and disrupt zinc absorption.
Pantothenic acid and biotin
Pantothenic acid is used in the breakdown of carbohydrates, lipids and some amino acids. It is also used for the synthesis of coenzyme A for biochemical reactions in the body. Biotin functions as a coenzyme in carboxylation reactions (-COOH), which are also useful in many of the body's functions. (Pantothenic acid, biotin and folic acid are often used in tandem by the body.) Bacteria in our intestines produce both pantothenic acid and biotin. There is no known disorder associated with pantothenic acid deficiency. The vitamin is found in abundance in meats, legumes and whole-grain cereals. Mega-doses of pantothenic acid can cause diarrhea.
A deficiency of biotin is rare but can cause a skin disorder called scaly dermatitis. Biotin deficiency may be found in individuals who eat large quantities of egg whites. These contain the substance avidin, which "ties up" the body's biotin. Biotin is found in beef liver, egg yolk, brewer's yeast, peanuts, cauliflower and mushrooms.
Getting Enough B Vitamins
As you can see, the B vitamins are essential for an astonishing array of life functions. Fortunately, most of us will get all of the B vitamins we need by eating a well-balanced diet. Some people swear by a B-complex supplement every day, but based on the wide variety of foods containing these vitamins, a supplement may not be necessary.
Researchers from the Hope Heart Institute say that up to 30 percent of people over age 50 have lost the ability to absorb adequate vitamin B12 from meat or dairy products. Other people need only 2.4 mg. a day -- the amount found in three ounces of beef -- but researchers recommend that older Americans eat fortified cereal or grains or take a daily vitamin supplement. (If you need extra calories and protein, a supplement drink, containing all the appropriate vitamins, is an alternative.) Check the chart below for a quick, but thorough, look at the basics of the B-complex vitamins:
|Recommended Daily Allowance (RDA)* in mg (B12 is in µg)||Food Sources||Importance||When You Take Too Much||When You Take Too Little|
|Thiamine (B1)||I=0.3-0.4; C=0.7-1.0; A=1.0-1.5||cereal, bread, meat, rice, yeast, corn, nuts||carbohydrate metabolism, nervous system||none known||beriberi (anemia, paralysis), movement & memory effects|
|Riboflavin (B2)||I=0.4-0.5; C=0.8-1.2; A=1.2-1.8||grains, milk, meat, eggs, cheese, peas||maintains skin, mucous membranes, eyes, nerve sheaths||None known||skin & oral problems, anemia|
|Niacin (B3)||I=5-6; C=0.8-1.2; A=1.2-1.8||meat, milk, eggs, fish, legumes, potatoes||healthy skin, nerves & GI tract, metabolism of food||flushing, itching, cramps, nausea, skin eruptions||pellagra (diarrhea, dermatitis, dementia)|
|Pyridoxine (B6)||I=0.3-0.6; C=1.0-1.4; A=1.4-2.0||organ meats, brown rice, fish, butter, soybeans||metabolism of food, amino acids||nerve damage||skin & nerve damage, confusion, mouth irritation|
|Folic acid (B9)||I=25-35; C=50-100; A=150-180||yeast, liver, green vegetables, whole grain cereal||DNA, hemoglobin synthesis, formation of blood cells, protein metabolism||convulsions, disrupted zinc absorption||anemia, mouth irritation, poor growth|
|Pantothenic acid||N/A; made by our intestines||meats, legumes, whole-grain cereals||breakdown of carbohydrates, lipids, amino acids||diarrhea||none known|
|Biotin||N/A; made by our intestines||beef liver, egg yolk, brewer's yeast, mushrooms||functions as coenzyme in caroboxylation reactions||none known||scaly dermatitis|
|B12||I=0.3-0.5; C=0.7-1.4; A=2.0||liver, meat, eggs, poultry, milk||metabolism of food, blood cell formation, DNA synthesis||none known||pernicious anemia, mouth irritation, brain damage|
*I=infant; C=child; A=adult. Please note that vitamin ranges account for differences in age and gender. Some of the vitamins should be increased during pregnancy and for lactating mothers.
For more information on vitamins and related topics, check out the links on the next page.
Related HowStuffWorks Articles
- Prenatal Vitamins
- How Vitamin B1 Works
- How Vitamin B12 Works
- How Vitamin B2 Works
- How Vitamin B3 Works
- How Vitamin B5 Works
- How Vitamin B6 Works
- How Folate Works
- How Biotin Works
- How Nutrition Works
More Great Links
- Mayo Clinic Food and Nutrition Center
- Older Americans & B Vitamins
- Kellogg's Nutrition Page
- Post Cereals Home Page