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A Comprehensive Guide to the B Vitamins

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Written by
Medically reviewed by
Dr. Kealy Mann, ND

Updated on June 1, 2020

B vitamins are a group of water-soluble vitamins essential for several important functions in the body, including supporting metabolism and helping the body produce energy. (23)

You may already be familiar with certain B vitamins, such as vitamin B12, but, in total, there are eight different B vitamins. Collectively, this group of B vitamins is often referred to as “vitamin B complex”.

The eight B vitamins are:

  • B1 (thiamin)
  • B2 (riboflavin)
  • B3 (niacin)
  • B5 (pantothenic acid)
  • B6 (pyridoxine)
  • B7 (biotin)
  • B9 (folate)
  • B12 (cobalamin)

B vitamins are water-soluble, so they dissolve quickly in the body. Unlike fat-soluble vitamins (vitamins A, D, E, and K), water-soluble vitamins are absorbed by the body’s tissues and are not stored for long-term use. Any excess water-soluble vitamins are excreted in our urine. For this reason, regular intake of each B vitamin is necessary to maintain optimal levels in the body. (3)

B vitamins list

The table below outlines the best food sources of vitamin B, as well as their unique functions.

B vitamins have unique functions and are found in several foods. (25)(15)(17)(37)(28)(35)(20)(36)(26)(39)(24)(30)(34)(32)(40)

Vitamin B benefits

Beyond helping break down the carbohydrates, fat, and protein we eat and converting them into energy, each B vitamin has unique functions. Below, we look at each of these vitamins in more detail.

Vitamin B1

Also known as thiamin, vitamin B1 is important for the growth, development, and function of your body’s cells. (38)

Research suggests a link between thiamin and type 2 diabetes. Low levels of thiamin is common in individuals with type 2 diabetes. Supplementing with thiamin may be beneficial in the treatment and prevention of type 2 diabetes; however, more research is needed to substantiate these claims. (13)

The recommended daily intake for vitamin B1 (thiamin) for adult men and women is 1.2 mg and 1.1 mg, respectively. (25)

Vitamin B2

Vitamin B2, also known as riboflavin, is important for growth, development, and cellular function. It also aids in the release of energy from dietary protein and the production of red blood cells. (37)

Consuming adequate doses of riboflavin through food or supplements has been associated with a decreased risk of developing cataracts, a condition characterized by cloudy lenses of the eye and progressive vision loss. (10)

Riboflavin may also help to prevent premenstrual syndrome, a set of physical and psychological symptoms affecting approximately 15% of women of reproductive age. One study showed that consuming riboflavin-rich foods significantly decreased the risk of experiencing symptoms of PMS by 35%. (1)

The recommended daily intake for vitamin B2 (riboflavin) for adult men and women is 1.3 mg and 1.1 mg, respectively. (29)

Vitamin B3

Vitamin B3, or niacin, is converted into coenzyme nicotinamide adenine dinucleotide (NAD), a compound needed by over 400 enzymes to conduct several cellular functions, including DNA repair and gene expression. (5) Niacin also supports digestive, skin, and nerve function. (35)

Niacin may also decrease the risk of cardiovascular disease by reducing LDL (unhealthy) cholesterol, total cholesterol, and triglycerides while increasing HDL (healthy) cholesterol. Niacin’s neuroprotective properties may prevent some age-associated neurological diseases, such as Alzheimer’s and Parkinson’s disease. (4)

The recommended daily intake for vitamin B3 (niacin) for adult men and women is 16 mg and 14 mg, respectively. (28)

Vitamin B5

Also called pantothenic acid, vitamin B5 plays an important role in the production of hormones and cholesterol. Pantothenic acid is responsible for synthesizing coenzyme A (CoA), necessary for creating and breaking down fatty acids. (36)

Pantothenic acid may lower cardiovascular disease risk by reducing total cholesterol and LDL cholesterol. (12) Furthermore, dietary intake of pantothenic acid has been shown to reduce C-reactive protein (CRP), an inflammatory marker that contributes to the development of atherosclerosis (hardening of the arteries). (11)

The recommended daily intake for vitamin B5 (pantothenic acid) for adult men and women is 5 mg per day. (27)

Vitamin B6

Vitamin B6, less commonly known as pyridoxine, has many important functions in the body, including maintaining normal nerve function, assisting in antibody and hemoglobin production, and maintaining healthy blood sugar. (39)

Vitamin B6 may have mood-boosting properties. Low levels of vitamin B6 are commonly found in individuals suffering from depression. Vitamin B6 helps produce neurotransmitters such as serotonin and dopamine, responsible for regulating emotions. (9) One study showed that, in combination with tryptophan and nicotinamide (a form of vitamin B3), vitamin B6 may improve mood in patients with depression. (45)

Chronic (long-term) stress has also been shown to deplete B6 levels. (44) One study found that supplementing with vitamin B6, in combination with magnesium, significantly reduced perceived stress levels. (43)

The recommended daily intake for vitamin B6 (pyridoxine) for adult men and women is 1.3 mcg per day. Adults over the age of 50 require slightly more —1.7 mg for men and 1.5 mg for women. Taking high doses of supplemental vitamin B6 may lead to toxicity. (26)(8)

Vitamin B7

Vitamin B7 is more commonly known as biotin. It works with vitamin B5 (pantothenic acid) to synthesize and break down fats. (36) Biotin is commonly associated with hair and nail growth, although research is limited. (6)

Some research suggests that biotin may help regulate blood sugar in individuals with type 1 diabetes. One study found that biotin supplementation significantly decreased fasting blood sugar and also reduced LDL (unhealthy) cholesterol in type 1 diabetics after three months. (7)

The recommended daily intake for vitamin B7 (biotin) for adult men and women is 30 mcg per day. (24)

Vitamin B9

Also known as folate, vitamin B9 is needed for DNA production and proper cell division. Folic acid, which is commonly found in fortified foods and supplements, is the synthetic form of folate. For pregnant women or those who are trying to conceive, getting enough folate or folic acid is especially important. Obtaining enough of this nutrient before and during pregnancy can help prevent neural tube defects, a birth anomaly affecting the baby’s brain or spine. (31)

Supplementing with folic acid may also improve cognitive function in adults. One study found that folic acid supplementation over a two-year period increased verbal IQ and decreased beta amyloid buildup, a type of protein that contributes to impaired brain function and the progression of Alzheimer’s disease. (14)

The recommended daily intake of folate for adult men and women is 400 mcg per day. Pregnant and lactating women need to consume 600 mcg and 500 mcg per day, respectively. (30)

Vitamin B12

Vitamin B12, also known as cobalamin, can be stored in the liver, unlike other B vitamins. Vitamin B12 also assists in the formation of red blood cells and the maintenance of a healthy central nervous system. (40)

The two most common forms of B12 are methylcobalamin and cyanocobalamin. Methylcobalamin is naturally occurring, whereas cyanocobalamin is a synthetic form of vitamin B12 and is commonly found in fortified foods and some supplements. Both forms of B12 have similar bioavailabilities and physiological effects; however, preliminary findings suggest that cyanocobalamin has slightly lower bioavailability than methylcobalamin. (41)

It’s important to note that there are two additional forms of B12 – adenosylcobalamin and hydroxycobalamin. Hydroxycobalamin is a precursor to B12 and is converted to methylcobalamin and adenosylcobalamin. Similarly to methylcobalamin, the bioavailability of adenosylcobalamin and hydroxycobalamin appears to be slightly higher than that of cyanocobalamin. For individuals who can’t tolerate methylcobalamin, adenosylcobalamin and hydroxycobalamin may be suitable alternatives. (41) Your integrative healthcare practitioner can help you determine which form of B12 is right for you.

Vitamin B12 may be protective against heart disease. One study found that vitamin B12 supplementation may help lower homocysteine levels. Elevated homocysteine has been shown to be a contributor to arterial damage and blood clot formation. (2)

The recommended daily intake of vitamin B12 for adult men and women is 2.4 mcg per day. (32)

woman looking at her laptop and thinking

There are eight different types of B vitamins that help to support metabolism and contribute to the body’s ability to produce energy.

Vitamin B deficiency

Most people get enough vitamin B from the foods they eat. However, vitamin B deficiencies can occur as a result of poor diet or an underlying health condition. (42)

Signs and symptoms of vitamin B deficiency, include:

  • Anemia (insufficient red blood cells)
  • Confusion
  • Depression
  • Dry, flaky skin
  • Fatigue
  • Mouth sores
  • Gastrointestinal symptoms (e.g., constipation, diarrhea, nausea, and vomiting)
  • Numbness and tingling of the extremities
  • Restlessness
  • Skin rashes
  • Weakness (33)(20)(18)(21)(17)(46)

woman itching her arm

Skin rashes and scaly skin are among the symptoms of vitamin B6 deficiency.

Individuals at greatest risk of developing a vitamin B deficiency include pregnant and breastfeeding women, older adults, and individuals following certain diets (e.g., vegan, ketogenic diet). (47) Some underlying conditions, such as alcoholism, Celiac disease, and Crohn’s disease, may affect the body’s ability to absorb B vitamins. Additionally, individuals who have undergone bariatric surgery for weight loss are at greater risk of vitamin B deficiency. (33)(22)(19)

Many foods provide B vitamins. Eating a variety of nutrient-dense and vitamin B-rich foods can help ensure you get enough of the B vitamins each day. (42) Dietary supplements, such as a B complex or a multivitamin containing B vitamins, can make up for dietary inadequacies. B vitamins are also available as individual supplements if you are deficient in only one specific B vitamin.

MTHFR gene variant

A gene known as methylenetetrahydrofolate reductase (MTHFR) helps your body convert folic acid and folate (vitamin B9) into the active form, 5-methyltetrahydrofolate (5-MTHF). A large proportion of the population has a specific MTHFR gene variant (a change in the DNA sequence) that inhibits the conversion of folic acid and folate to 5-MTHF. Individuals with this gene variant are more likely to be deficient in folate, as well as vitamin B6 and B12. (16)(29)

Those with this specific gene variant can benefit from taking supplemental folate in the form of methyl-folate, also known as 5-MTHF, as opposed to synthetic folic acid supplements. (29)

Your healthcare practitioner can help you determine whether you have the specific MTHFR gene polymorphism through genetic testing. (16)

The bottom line

B vitamins are necessary for energy production, proper cellular function, and the maintenance of cells and tissues. Eating a wide variety of healthy, vitamin B-rich foods can help you get all the B vitamins recommended for optimal health. Vitamin B supplements may be especially beneficial for some individuals, including those who follow certain diets or have certain underlying health conditions. If you are a patient, consult your integrative healthcare practitioner before adding a B vitamin supplement to your daily regimen.

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