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B Vitamins: Types, Health Benefits and Deficiency

B vitamins (or vitamin B complex) are a group of water-soluble vitamins that are essential for the body to function. They include vitamins B1, B2, B3, B5, B6, B7, B9 and B12. Some of them are better known under their chemical names such as niacin (B3), biotin (B7) or folate (B9). Although all of these vitamins play an important role in metabolism and many of them work in tandem when assisting chemical reactions in the body, they also act independently and are chemically distinct. Due to their interdependence, B vitamins are frequently discussed as a group.

B vitamins act as coenzymes in chemical processes that take place inside cells. Some of these reactions are necessary for growth and the metabolism of carbohydrates, fats and proteins. In addition to that, some B vitamins are structural components of cells.

The human body either does not produce B vitamins itself or does not produce enough to meet its needs. Most of them are used and quickly eliminated from the body. The only exception is vitamin B12, which can be recycled and reused within the body.

Often, many of the B vitamins are found in the same foods. A balanced diet will typically fulfil the body’s needs for these vitamins. They are also available in supplement form, both as individual vitamins and as the entire B-complex group. Being water-soluble, B vitamins are not stored in tissues and must be consumed or manufactured by the body regularly.

The ability of the gastrointestinal tract to absorb several of the B vitamins from diet diminishes with age. Therefore, vitamin supplements or fortified foods are often recommended for patients over age 50. Doctors may also recommend supplements for vegans or vegetarians to replace those B vitamins that are naturally available only in animal products and for patients who are unable to use or absorb the nutrients from food sources.

Since B vitamins work in complex interrelationships, a deficiency of one may impact the function of others. However, serious deficiencies of B vitamins are rare in the developed world. The body may also react to too much of some of the B vitamins. Because all B vitamins are water-soluble, reports of toxicity related to individual B vitamins are rare. However, overdoses of the vitamins B2, B3 and B6 have been reported to cause a diverse range of symptoms.

Types of B Vitamins

The B vitamins take part in numerous chemical reactions within the body. All eight B vitamins are involved directly or indirectly in energy metabolism and growth while also having the following other functions:

  • Vitamin B1 (thiamine) helps release energy from carbohydrates, aids in communication between nerves and muscles and plays a vital role in the production of hydrochloric acid necessary for chemical digestion of food.
  • Vitamin B2 (riboflavin) also helps convert carbohydrates to energy. In addition, it is involved in breaking down proteins and fats, cell development and function (and therefore also growth) and in the production of red blood cells.
  • Vitamin B3 (niacin, niacinamide, nicotinamide or nicotinic acid) helps metabolize glucose, alcohol and fat and is needed to create new cells and make fatty acids and steroids. Nicotinamide and nicotinic acid are the forms occurring naturally in food whereas niacin and niacinamide are used in dietary supplements. B3 is one of the few B vitamins that the body can produce itself but in smaller amounts than it needs.
  • Vitamin B5 (pantothenic acid) is essential for the metabolism of carbohydrates, fats and proteins and for the production of lipids, neurotransmitters and hemoglobin. Vitamin B5 can be made by the body, but not enough is produced to meet its needs.
  • Vitamin B6 (pyridoxine, pyridoxamine or pyridoxal) is involved in making vitamin B3, amino acids, hemoglobin, synthesizing the neurotransmitters serotonin, dopamine and norepinephrine, and maintaining blood glucose levels.
  • Vitamin B7 (biotin) is required for metabolism of some amino acids and fatty acids and is also involved in the synthesis of glucose. It is made by bacteria in the gastrointestinal tract, but not in amounts large enough to meet the body’s needs.
  • Vitamin B9 (folate or folic acid) is vital for creating and maintaining cells because of its involvement in the synthesis of DNA and proteins. Therefore, it is essential in the earliest stages of pregnancy for good fetal health. Folic acid is the synthetic form of the vitamin B9. The body produces some folate itself, though not enough to meet its needs.
  • Vitamin B12 (cobalamin) is involved in the metabolism of fatty acids and amino acids and is essential for the nervous system, creation of red blood cells and making DNA.

Dietary Sources of B Vitamins

The B vitamins are found in a variety of different foods. Therefore, the best way to satisfy the needs of the human body is to eat a well-balanced diet.

Vitamin Food Source
B1 Whole grain products, seafood, legumes (e.g., beans, peas and peanuts), squash, red meat (especially pork and liver), eggs, nuts, seeds, brewer’s yeast, spinach
B2 Red meat (especially organ meat such as liver), poultry, eggs, milk and dairy products, mushrooms, leafy vegetables (e.g. spinach, broccoli), asparagus, almonds, whole grain products, fish, sun-dried tomatoes, enriched cereals
B3 Fish (especially tuna and salmon), poultry (chicken, turkey), red meat (especially pork, beef and lamb liver), mushrooms, eggs, milk and dairy products, avocados, leafy vegetables, legumes (peas, peanuts), brewer’s yeast, sunflower seeds, whole grain products or enriched cereal products, broccoli, sweet potatoes, tomatoes, asparagus
B5 Brewer’s yeast, red meat (especially liver), fish and shellfish, bran, mushrooms, poultry, milk and dairy products, legumes, corn, potatoes, whole grain products, egg yolks, tomatoes (and juice), leafy vegetables
B6 Fish (especially salmon and tuna), organ meats (especially beef liver), red meat, poultry, potatoes and other starchy vegetables, legumes, bananas, tomatoes, spinach, beans, fortified breakfast cereals, peanut butter
B7 Red meat (especially organ meats such as liver, kidney and heart), brewer’s yeast, egg yolks, fish, legumes, whole grain products (especially from barley), wheat bran, milk and dairy products, soy, nuts, cauliflower
B9 Leafy vegetables (e.g. spinach, broccoli, Brussels sprouts, and turnip greens), poultry, legumes (e.g., dried beans and peas), yeasts, red meat (especially liver), potatoes, tomatoes (and juices), avocado, fruits (e.g., citrus fruits and juices), mushrooms, fortified breakfast cereals
B12 Fish and shellfish, red meat, liver, poultry, eggs, milk and dairy products, fortified breakfast cereals

In addition, some foods such as many breads, cereals or rice are enriched or fortified with B vitamins. They are often critical in a vegan or vegetarian diet to provide those B vitamins that are naturally found mainly or only in animal products.

However, the way foods are prepared can affect their B vitamin content. Boiling, microwave cooking and overcooking, long storage (exposure to oxygen and/or light), freezing and canning can dramatically reduce the nutrient content of all foods.

Health Effects of B Vitamins

All B vitamins are essential to body function. Without them, cells would not be able to divide, grow, communicate and metabolize food into energy. Supplementing certain or all B vitamins may also be a part of established treatments for a number of medical conditions, including:

  • Atherosclerosis. Vitamin B3 can be prescribed as part of a treatment aimed at slowing the hardening and narrowing of the arteries.
  • High cholesterol. For some patients, vitamin B3 can be used in conjunction with other cholesterol-lowering drugs to increase high-density lipoprotein (HDL, the “good cholesterol”) levels and to decrease low-density lipoproteins (LDL, the “bad cholesterol”).
  • Metabolic disorders. With conditions such as lactic acidosis, Leigh disease or maple syrup urine disease the body cannot produce the thiamin pyrophosphate needed for energy metabolism. Supplementation of vitamin B1 may increase the production of thiamin pyrophosphate.
  • Neonatal jaundice (yellowing of the infant’s eyes and skin). When phototherapy is used to treat this condition, it is often applied in conjunction with vitamin B2 supplements because phototherapy light may break down riboflavin (B2).
  • Pregnancy. B vitamins are particularly important in the earliest stages of pregnancy to reduce the risk of neural tube defects and are, therefore, included in most prenatal supplements. Folate (B9) is highly recommended to women who could become pregnant to lower the risk of spina bifida and other neural tube-related birth defects.
  • Sideroblastic anemia. Patients with this disorder are unable to make normal red blood cells. Treatment involving B6 supplements may assist in the production of red blood cells.
  • Vitamin deficiency. Some people do not get enough B vitamins to meet their body’s needs due to a poor diet or a condition that hinders proper absorption or use of nutrients. Supplementing B vitamins may be temporary or life-long, depending on the cause of the deficiency.

In the meantime, research continues to investigate the link between B vitamins and a variety of other conditions including heart disease, blood clots, strokes, migraines, memory loss, Alzheimer’s dementia, rheumatoid arthritis as well as cancer. Many experts also believe that certain B vitamins may help prevent premature aging of the skin and hair and promote immune system health. (Regarding potential health benefits of vitamin B12 you can check this article).

Certain medications, substances (e.g., alcohol) or therapies can disrupt the complex relationships between some B vitamins and the human body by preventing their absorption, or destroying them before they can be used, or preventing them from performing their intended functions. For example, overuse or abuse of alcohol can lead to severe B vitamin deficiency. Greater intake of all B vitamins may be needed in conjunction with certain treatments (e.g., dialysis) or drugs (e.g., diuretics), while some medications may only interact with specific vitamins.

Overdose and Deficiency of B Vitamins

Too little or too much of the B vitamins stresses cells and tissues and may lead to serious and even life-threatening conditions. The symptoms of a deficiency or overdose may include:

Vitamin Overdose Deficiency
B1 None reported Apathy, fatigue, depression, poor mental concentration, irritability, anorexia
B2 Burning or prickling sensations, itching, numbness, sensitivity to light, yellow discoloration of urine Sensitivity to light, corneal vascularization, glossitis, cheilosis, sore throat, skin lesions
B3 Warm sensation, skin flushing and itching, dry skin, blurred vision Diarrhea, vomiting, abdominal pain, apathy, depression, fatigue, headache, loss of memory, dermatitis
B5 None reported Fatigue, depression, personality changes, sleep disturbance, neurological disorders, abdominal pain
B6 Fatigue, depression, headaches, irritability, numbness, muscle weakness in arms and legs, skin lesions Depression, confusion, seizures, cheilosis, glossitis, skin inflammation,  anemia
B7 None reported Lethargy, depression, hallucinations, tingling sensation in extremities, hair loss
B9 Masks B12 deficiency Weakness, fatigue, confusion, irritability, glossitis, anemia
B12 None reported Anemia, incontinence, muscle weakness, spasticity, vision problems, dementia

Toxicity of B vitamins, though rare, is typically the result of taking excessive supplements. Normally, overdoses of B vitamins stress the kidneys, but rarely cause permanent damage. B6 is unique among the B vitamins in that its overdose causes nerve damage. But, this damage can be reversed when supplementation is discontinued. In contrast, overdoses of the vitamin B9 (folate) may mask symptoms of B12 deficiency, potentially leading to permanent nerve damage.

However, when it comes to vitamin B deficiency, there is a relatively long list of associated conditions including beriberi (severe deficiency of B1), ariboflavinosis (severe B2 deficiency), pellagra (B3 deficiency) as well as deficiencies of the vitamins B5, B6, B7, B9 and B12. Since many of the B vitamins occur in the same foods and are involved in complex interactions, a deficiency of one often implies and may also cause a deficiency of others. For example, folate (B9) deficiency prevents the cells of the digestive tract from replicating, affecting the ability of the digestive system to absorb other B vitamins.

Recommended dietary allowances (RDAs) for individual B vitamins for adult men, women and children are shown in the tables below:

B Vitamins RDAs for Men

Vitamin 14-18 Years 19-50 Years 51+ Years
B1 (mg/d) 1.2 1.2 1.2
B2 (mg/d) 1.3 1.3 1.3
B3 (mg/d) 16 16 16
B5 (mg/d) 5 5 5
B6 (mg/d) 1.3 1.3 1.7
B7 (mcg/d) 25 (*) 30 (*) 30 (*)
B9 (mcg/d) 400 400 400
B12 (mcg/d) 2.4 2.4 2.4

* Adequate intake (AI) as no RDA has been established

B Vitamins RDAs for Women

Vitamin 14-18 Years 19-50 Years 51+ Years Pregnant Lactating
B1 (mg/d) 1.0 1.1 1.1 1.4 1.4
B2 (mg/d) 1.0 1.1 1.1 1.4 1.6
B3 (mg/d) 14 14 14 18 17
B5 (mg/d) 5 5 5 6 7
B6 (mg/d) 1.2 1.3 1.5 1.9 2.0
B7 (mcg/d) 25 (*) 30 (*) 30 (*) 30 (*) 35 (*)
B9 (mcg/d) 400 400 400 600 500
B12 (mcg/d) 2.4 2.4 2.4 2.6 2.8

* Adequate intake (AI) as no RDA has been established

B Vitamins RDAs for Children

Vitamin 0-6 Months 7-12 Months 1-3 Years 4-8 Years 9-13 Years
B1 (mg/d) 0.2 (*) 0.3 (*) 0.5 0.6 0.9
B2 (mg/d) 0.3 (*) 0.4 (*) 0.5 0.6 0.9
B3 (mg/d) 2 (*) 4 (*) 6 8 12
B5 (mg/d) 1.7 1.8 2 3 4
B6 (mg/d) 0.1 (*) 0.3 (*) 0.5 0.6 1.0
B7 (mcg/d) 5 (*) 6 (*) 8 (*) 12 (*) 20 (*)
B9 (mcg/d) 65 (*) 80 (*) 150 200 300
B12 (mcg/d) 0.4 (*) 0.5 (*) 0.9 1.2 1.8

* Adequate intake (AI) as no RDA has been established