Vitamin B Explained: Benefits, Deficiency, And Sources

When it comes to micronutrients, the B vitamins are some of the most important (via the New World Encyclopedia). Collectively, they help with a number of vital processes, including the extraction of energy from food, cell growth and division, and the proper functioning of the immune and nervous systems. The B vitamins are essential for life and can't be created by our bodies, so they must be obtained from food or supplements. But because these vitamins are water-soluble rather than fat-soluble, the body can't store them, which means they need to be consumed regularly.

Today, there are eight recognized B vitamins, all of which are chemically similar to one another. They are B1 (thiamin or thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine, pyridoxal, and pyridoxamine), B7 (biotin), B9 (folate or folic acid), and B12 (cobalamin). Some, like niacin and biotin, are more commonly known by their name, while others, such as B6 and B12, are more commonly referred to by their number. Ever wonder why there are gaps in the numbering? The "missing" numbers represent substances that were once thought to be B vitamins but were later found to either not be vitamins at all, or to be nonessential (in other words, micronutrients our bodies can make themselves from other substances). These include adenosine monophosphate (formerly vitamin B8) and para-aminobenzoic acid (formerly vitamin B10). In fact, there are 20 substances that at one time were considered B vitamins but have subsequently been redesignated.

Vitamin B1 – thiamin

Thiamin (also spelled thiamine) is essential for the growth, development, and function of every cell in the body because it helps cells turn the food we eat into usable energy (via the National Institutes of Health). Like all the other B vitamins, thiamin is water-soluble, but the liver is able to store very small amounts of this micronutrient. The recommended dietary allowance (RDA) of thiamin is 1.2 mg for adult men, 1.1 mg for nonpregnant adult women, and 1.4 mg for those who are pregnant or breastfeeding. Many foods naturally contain thiamin, and others have been fortified, so it's easy to meet the RDA for this B vitamin. In fact, only about 6% of Americans don't get enough thiamin.

When it does occur, thiamin deficiency can lead to a condition known as beriberi. Symptoms include muscle wasting and nerve damage, and in some cases it may lead to heart failure and death. Beriberi is not typically seen in the United States and other developed countries. Wernicke-Korsakoff syndrome is another manifestation of thiamin deficiency, and is usually the result of chronic alcoholism. It causes nerve damage and a form of psychosis that includes severe short-term memory loss, disorientation, and an inability to tell the difference between real and imagined memories. Without thiamin treatment, about 20% of individuals with Wernicke-Korsakoff syndrome will die in the initial phase of the condition, and about 25% of those with psychosis symptoms don't recover even with treatment.

Vitamin B2 – riboflavin

Riboflavin is needed to make two important coenzymes: flavin mononucleotide, or FMN, and flavin adenine dinucleotide, or FAD (via the National Institutes of Health). Coenzymes enhance the effects of enzymes, which are substances that trigger biochemical reactions. FMN and FAD play major roles in energy production, the growth and development of cells, and the absorption of fats and certain drugs. Riboflavin also helps maintain normal levels of the amino acid homocysteine in the blood. Very small amounts of riboflavin can be stored in the liver, heart, and kidneys. In addition to absorbing this B vitamin from food or dietary supplements, the friendly bacteria in our large intestines can also produce the riboflavin our bodies need. The recommended dietary allowance (RDA) for riboflavin is 1.3 mg for adult men, 1.1 mg for nonpregnant adult women, and 1.4 mg for those who are pregnant or breastfeeding. Less than 6% of Americans don't get enough riboflavin, so deficiency in the United States is extremely rare.

Riboflavin deficiency (ariboflavinosis) can be caused by not getting enough riboflavin, or can be the result of certain diseases and conditions, including hypothyroidism. Symptoms include skin issues, lesions at the corners of the mouth, cheilosis (swollen and cracked lips), hair loss, and red, itchy eyes. It can also cause swelling in the mouth and throat, reproductive problems, liver failure, and degeneration of the nervous system.

Vitamin B3 – niacin

The niacin we ingest is converted into two coenzymes, nicotinamide adenine dinucleotide, or NAD, and nicotinamide adenine dinucleotide phosphate, or NADP (via the National Institutes of Health). More than 400 enzymes need NAD to carry out their reactions. NAD assists with the breakdown of carbohydrates, fats, and protein; the control of gene expression; and communication between cells. NADP is necessary for creation of fatty acids and cholesterol in the body. In addition to getting niacin directly from food or supplements, our bodies can convert the amino acid tryptophan (found in many foods, including your Thanksgiving turkey) to NAD. The recommended dietary allowance (RDA) for niacin is 16 mg for adult men, 14 mg for nonpregnant adult women, 18 mg for pregnant women, and 17 mg for those who are breastfeeding. It's very easy to get enough niacin, and only about 1% of American adults don't meet dietary guidelines.

Severe niacin deficiency leads to a condition called pellagra. Although rare in industrialized nations today, pellagra was relatively common among impoverished people living in the southern United States and parts of Europe in the early 1900s because corn (which lacks niacin) made up most of their diet. Pellagra causes discoloration, rash, and roughness on sun-exposed skin. It also causes changes in the gastrointestinal (GI) tract that result in vomiting, diarrhea, constipation, and lack of appetite. Neurological and psychological symptoms include headaches, memory loss, apathy, aggression, and hallucinations.

Vitamin B5 – pantothenic acid

Although less well-known than some of the other B vitamins, pantothenic acid is nevertheless critical to health (via the National Institutes of Health). Vitamin B5 is necessary for a number of bodily processes, especially those related to the synthesis and breakdown of fatty acids. After being absorbed in the intestines, B5 is carried throughout the body by red blood cells. The adequate intake (AI) for pantothenic acid is 5 mg for adult men and nonpregnant women, 6 mg for pregnant individuals, and 7 mg for those who are breastfeeding.

Most plant and animal foods contain at least some B5, so deficiency is very rare and usually only seen with extreme malnutrition. In these cases, other nutritional deficiencies are also present, so it can be hard to identify exactly which symptoms are related to a lack of pantothenic acid specifically. Individuals with a rare inherited condition called pantothenate kinase-associated neurodegeneration (PKAN) are also at increased risk of B5 deficiency. Symptoms may include burning or numbness in the hands and feet, fatigue, headaches, irritability, sleep and GI problems, and lack of appetite.

Vitamin B6 – pyridoxine, pyridoxal, and pyridoxamine

Vitamin B6 is actually a collection of six different substances: two different versions of pyridoxine, pyridoxal, and pyridoxamine (via the National Institutes of Health). Collectively, B6 assists with more than 100 functions in the body. Most of these center around turning dietary protein into energy, but B6 is also involved in the production of neurotransmitters, white blood cells, and hemoglobin (the protein that allows red blood cells to carry oxygen, via Mayo Clinic). It also helps maintain normal concentrations of homocysteine, an amino acid that can cause damage to arteries if levels get too high. The recommended dietary allowance (RDA) for vitamin B6 is 1.3 mg for men and women between the ages of 18 and 50. Older men should aim for 1.7 mg, while older women should get at least 1.5 mg. Pregnant women need 1.9 mg, and those who are breastfeeding should get 2 mg daily.

Most Americans consume more than the RDA for vitamin B6, but about 24% of individuals who don't take vitamin B supplements and 11% of people who do still have low B6 levels. Heavy alcohol use, obesity, and pregnancy may cause B6 levels to be low. Even so, true vitamin B6 deficiency is uncommon in the United States. Signs of severe deficiency include a swollen tongue, cracked lips, dementia, depression, and anemia. Those most at risk for deficiency include individuals with kidney disease, certain genetic disorders, and conditions like celiac or Crohn's disease that interfere with absorption of micronutrients.

Vitamin B7 – biotin

Although biotin (also known as vitamin B7 and vitamin H) is usually thought of as the "hair, skin, and nails" vitamin, its value isn't just cosmetic (via the National Institutes of Health). Biotin is needed for a number of critical functions, including the use of fatty acids, glucose, and amino acids for energy. It also plays a role in gene expression and communication between cells. The adequate intake (AI) for biotin is set at 30 mcg for adult men and both nonpregnant and pregnant women, while breastfeeding women should aim for 35 mcg.

Severe biotin deficiency is rare and has never been seen in an otherwise healthy individual eating a normal diet. Pregnant women and individuals who consume too much alcohol are at greater risk for mild biotin deficiency, however. Symptoms take a while to appear and can include thinning hair, hair loss, skin rashes, brittle nails, and skin infections. Signs of more serious deficiency include high levels of acid in the urine, depression, hallucinations, and seizures. Although biotin deficiency is associated with hair, skin, and nail problems, there's very little evidence that taking biotin supplements will lead to thicker hair, clearer skin, and stronger nails in those who aren't actually deficient in this vitamin.

Vitamin B9 – folate

Folate occurs naturally in foods, while folic acid is a form of vitamin B9 that is added to fortified foods and used in dietary supplements (via the National Institutes of Health). Folate is necessary for the replication of DNA and RNA, as well as cell division. The recommended dietary allowance (RDA) for folate is 400 mcg for both men and nonpregnant women. Pregnant women, however, need substantially more folate (600 mcg), and breastfeeding mothers also have higher-than-average folate needs (500 mcg).

Although most adults get enough folate, about 17% of women between the ages of 19 and 30 don't meet the minimum suggested amount. Folate deficiency usually occurs alongside other nutritional deficiencies. It can lead to anemia, which in turn causes extreme fatigue, weakness, shortness of breath, and heart issues. Most people know about folate deficiency, however, because of the devastating effect it can have during pregnancy. Babies whose mothers don't get enough folate during pregnancy are at increased risk for preterm birth, low birthweight, and neural tube defects (conditions such as spina bifida that affect the formation of the brain and spinal cord). On the other end of the spectrum, approximately 5% of men and women age 51–70 and men over 70 consume more than the tolerable upper limit (UL) for folic acid of 1,000 mcg due to the dietary supplements they take.

Vitamin B12 – cobalamin

Vitamin B12, also known as cobalamin, is actually a collection of four related substances, all of which contain the mineral cobalt (via the National Institutes of Health). Vitamin B12 is needed for the development and proper functioning of the central nervous system. Myelin, the protective sheath that insulates nerves, requires cobalamin, as do developing red blood cells. The recommended dietary allowance (RDA) for vitamin B12 is 2.4 mcg for adult men and nonpregnant women, 2.6 mcg for pregnant women, and 2.8 mcg for breastfeeding mothers.

Because vitamin B12 is found naturally only in animal foods, vegans who don't consume B12 supplements or foods fortified with B12 are at increased risk for deficiency. But deficiency can also result from difficulty absorbing B12 (due to conditions such as celiac disease or gastrointestinal surgery) and long-term use of certain medications. A substance secreted by stomach cells called intrinsic factor is needed to absorb B12, and in some autoimmune conditions, the immune system attacks these cells, making it impossible for dietary B12 to enter the bloodstream. Vitamin B12 deficiency can cause anemia (known as pernicious anemia if it's the result of a lack of intrinsic factor) and neurological symptoms such as numbness or tinging in the hands and feet. Other symptoms include a swollen tongue, weight loss, infertility, and low numbers of white blood cells and platelets. But because the body can store as much as 5 mg of B12, it may take years for deficiency symptoms to appear.

Getting B vitamins from food

The eight B vitamins are found in a wide variety of foods and are needed in only very small amounts, so eating a balanced diet is usually all that's required to get enough of these micronutrients (per Well + Good). As Rachel Gargiulo, a certified nutrition consultant, explained in a 2018 interview with Well + Good, B vitamins "can be acquired through a range of food choices, mostly coming from animal sources ... such as beef, chicken, eggs, lamb, turkey, tuna, salmon, and sardines." Plant-based sources of B vitamins include legumes, seeds, nuts, whole grains, soy, and dark leafy greens, but B vitamins from these sources are harder for our bodies to absorb. So, if you don't eat animal products, you may want to consider opting for fortified foods or a dietary supplement. This is particularly true for B12 because, unlike the other seven B vitamins, it doesn't occur naturally in any plant-based foods. The foods most commonly fortified or enriched include cereal, rice, bread, non-dairy milks, and nutritional yeast.

Because they're water-soluble, the B vitamins are highly unstable and easily damaged by heat and other types of processing (via the Better Health Channel). Folate and thiamin are the most fragile, while niacin, B5, and biotin are the most robust B vitamins. Boiling and other cooking methods that involve water cause B vitamins to leach out of foods, so if you aren't consuming the cooking liquid, you'll lose a lot of these important micronutrients.

B vitamin supplements

B vitamins are widely available as dietary supplements, either individually, as a B complex with all eight B vitamins, as part of a multivitamin, or packaged with other micronutrients in targeted blends (particularly those promising energy, mental health, or beauty benefits) (via Healthline). But should you be taking them? According to the Better Health Channel, supplements aren't miracle cures or a replacement for a healthy diet. It's always best to get B vitamins (and other micronutrients) from food if possible. But for those who are actually deficient or who have increased needs for certain B vitamins (such as folate during pregnancy), supplements can be helpful. It's important, however, not to self-diagnose a deficiency and to always consult with your doctor before you begin taking a supplement.

Because B vitamins are water-soluble, your body will flush out what it doesn't need through your urine (via Healthline). And don't be alarmed if your pee is bright yellow — that's a common (and harmless) side-effect of your body breaking down B vitamins. It's unlikely you'll get too many B vitamins through supplements, but there are still risks to taking excessively high doses. Extremely large amounts of niacin, for instance, can cause skin flushing, vomiting, high blood sugar, and liver damage. Too much B6 can lead to light sensitivity, skin lesions, and nerve damage. So, although vitamin B supplements are unlikely to cause harm, if you aren't actually deficient, you may be quite literally pissing away your money on something your body doesn't need.

What about B vitamin injections and infusions?

B vitamins can also be given as injections into a muscle or infusions through an IV, but in most cases such treatments are controversial, and more research is required into their efficacy (via SF Gate). These injections or infusions may include a single B vitamin, the full B complex, or particular B vitamins mixed with other vitamins and minerals such as magnesium, calcium, and vitamin C. Some complementary and alternative practitioners tout injections or infusions as a way to boost energy, cure a hangover, stimulate the immune system, lose weight, and combat chronic conditions like fibromyalgia. The evidence supporting such claims, however, is weak at best. There are also risks when it comes to getting your B vitamins through a needle. Injection or IV sites can become inflamed or infected, and allergic reactions are more likely when substances are injected directly into the body rather than taken by mouth.

But for individuals with vitamin B12-deficiency anemia caused by malabsorption or lack of intrinsic factor (pernicious anemia), vitamin B12 shots are the standard treatment (via the Mayo Clinic). Initially these shots may be given every other day, but eventually they may only be needed once a month to maintain healthy levels.

Do B vitamins reduce your risk for cardiovascular disease?

Since high circulating levels of the amino acid homocysteine are a possible risk factor for cardiovascular disease, some experts suspect that vitamin B6, B12, and folate may reduce your chances of heart disease because they help lower homocysteine levels in the blood (via the National Institutes of Health). Unfortunately, the research to date hasn't shown a strong link between supplemental B vitamins and reduced risk for cardiovascular disease. When it comes to heart disease risk, niacin may be more promising (via the Cleveland Clinic). Taken at high doses, it raises HDL ("good") cholesterol and lowers triglycerides. But it can have unwelcome side-effects, like facial flushing and itchiness, so it's usually only prescribed for those who are reluctant to take other cholesterol medications. Vitamin B5 (pantothenic acid) may also reduce cholesterol levels and, by extension, lower heart disease risk (via the National institutes of Health).

The connection between heart disease and B vitamins is a two-way street. According to research reported on by the Harvard Medical School, as many as 33% of individuals with heart failure have below-normal vitamin B1 (thiamin) levels, while 27% are deficient in vitamin B2 (riboflavin), and 38% were low on vitamin B6 (pyridoxine).

Can B vitamins prevent or fight cancer?

You may have heard that some B vitamins have powerful anti-cancer effects but, as with the link between B vitamins and reduced risk for cardiovascular disease, the connection between B vitamins and cancer is tenuous at best (via the National Institutes of Health). Riboflavin, for instance, may be able to prevent cancer by protecting DNA from damage caused by carcinogens, but studies have been inconclusive. Higher intake of folate has been associated with a decreased risk of lung, pancreatic, esophageal, stomach, cervical, ovarian, breast, bladder, and especially colorectal cancer (via the National Institutes of Health). Modest intake of folate while healthy may keep cancer at bay but, because folate is needed for cell division, taking high doses when cancer is present may actually promote the growth of the cancerous cells.

When it comes to vitamin B12, the research is particularly divided (via the National Institutes of Health). Some studies have linked higher-than-normal blood levels of B12 with as much as a fourfold increase in cancer risk. On the other hand, other studies have linked below-average B12 levels with increased risk for stomach, colorectal, and prostate cancer. And a number of studies have found no connection at all between B12 levels and cancer risk.

Taking B vitamins may boost your brain power and improve your mental health

Eating lots of vitamin B-rich foods or taking a B complex supplement may be one of the best things you can do for your brain. In a study published in Psychopharmacology in 2010, researchers gave healthy male subjects a high-dose B-complex supplement for 33 days and tracked their mood, stress levels, general mental health, and cognitive performance. Compared to the placebo group, those taking the B vitamins performed better on the cognitive tests and rated themselves as less stressed, more energetic, and less mentally fatigued.

And while B vitamins are no replacement for therapy or prescription medications, they may reduce symptoms of anxiety and depression in some individuals. In a 2013 study published in ISRN Psychiatry, researchers gave individuals diagnosed with depression either a high-dose B complex supplement or a placebo for 60 days. Those taking the supplement "showed significant and more continuous improvements in depressive and anxiety symptoms, compared to placebo."

Even for those on antidepressants, some B vitamins may make these medications more effective over the long run. A 2014 study published in The British Journal of Psychiatry found that vitamin B6, B12, and folic acid enhanced the effectiveness of antidepressant medications over a one-year period. Individuals taking these supplements were more likely to achieve relief from their symptoms and less likely to have a relapse of symptoms.