Your Ultimate Guide to the B-Complex Vitamins: Sources, Dosage and Benefits

Most of us probably think of vitamins as single nutrients, like vitamin C and vitamin D, but B vitamins are actually a group of eight different nutrients. Together, they're responsible for helping your metabolism function properly, according to the National Institutes of Health (NIH).

B vitamins are in a class called water-soluble vitamins, which means your body doesn't store them. Instead, any surplus gets flushed out of your system. That's why it's especially important to get adequate amounts of each B vitamin through your diet — or supplements, if necessary — to make sure you don't develop a deficiency.

Keep scrolling for a closer look at all the B vitamins, their benefits, signs of deficiency, sources and appropriate dosage.

Vitamin B1, or thiamin, is important to your overall metabolism, which refers to how the body uses food for energy, according to the NIH. This means those who burn more energy have an increased need for thiamin. The nutrient is also involved in nerve and muscle function.

Someone with a slight thiamin deficiency may experience headaches or fatigue and be irritable, per the NIH. Those with a major deficiency may have nervous system problems such as:

• Exaggerated reflexes
• Numbness
• Tenderness
• Seizures

B1 deficiency is also linked to a condition called beriberi, characterized by muscle weakness, loss of coordination, pain, mental disorientation and possible paralysis, per the NIH.

While most people get enough thiamin through food, you can also take it as a supplement orally or by injection. Injections can be administered by your health care provider, and supplements should only be taken with approval from your doctor, according to the Mayo Clinic.

People with a B1 deficiency may benefit from taking a thiamin supplement, according to the Mayo Clinic, as can people who:

• Have alcohol use disorder
• Are undergoing dialysis treatment
• Have HIV/AIDS
• Have had their stomach removed
• Have an artificial kidney
• Have anorexia
• Have intestinal or liver disease

According to the NIH, vitamin B1 may help with:

• Carbohydrate metabolism
• Nerve and muscle function
• Stabilizing blood sugar levels in people with type 2 diabetes
• Nerve damage caused by diabetes

Most Americans get enough thiamin every day in the form of:

• Whole and enriched grains
• Pork
• Beef
• Legumes
• Seeds
• Nuts

The recommended dietary allowance (RDA) of thiamin, according to the NIH, is:

• ‌Adults assigned male at birth:‌ 1.2 to 1.5 milligrams
• ‌Adults assigned female at birth:‌ 1 to 1.1 milligrams
• ‌Pregnant people:‌ at least 1.5 milligrams

Side effects of vitamin B1 are rare according to the Mayo Clinic. Still, contact your doctor if you experience:

• Coughing
• Difficulty swallowing
• Hives
• Itching skin
• Swelling of face or lips
• Wheezing or difficulty breathing

Riboflavin (aka vitamin B2), like thiamin, plays a role in metabolism. It's involved in the growth and development of red blood cells, and in converting carbohydrates into energy. It also plays an important role in cell function, growth and development and metabolism of fats, drugs and steroids, per the NIH.

Those who don't get enough riboflavin can develop a condition called ariboflavinosis, according to the NIH. Symptoms of B2 deficiency include:

• Cracks on the corners of your mouth
• Swollen tongue and lips
• Liver disorders
• Greasy scales on your skin, usually near the nose, ears and mouth
• Anemia
• Vision problems like cataracts

If you have congenital heart disease, alcohol use disorder, anorexia or some cancers, you may want to speak with your doctor about supplementing, according to the NIH.

According to the NIH, vitamin B2 helps with:

• Carbohydrate metabolism
• Red blood cell growth and development
• Cell function

In the U.S., much of our riboflavin comes from milk. UV light destroys riboflavin, though, so look for milk in opaque containers, the NIH advises. If you don't eat dairy, you can get your B2 from:

• Broccoli
• Dark leafy greens
• Fish
• Poultry
• Eggs

The recommended dietary allowance (RDA) of riboflavin, according to the NIH, is:

• ‌Adults assigned male at birth:‌ 1.3 milligrams
• ‌Adults assigned female at birth:‌ 1.1 milligrams
• ‌Pregnant people:‌ 1.4 milligrams
• ‌People who are lactating:‌ 1.6 milligrams

If you're getting more than the RDA of riboflavin, it's not likely to cause any side effects, according to the NIH.

So far, there have been no recorded instances of toxicity from excess riboflavin, possibly because riboflavin isn't easily absorbed in the gastrointestinal tract.

Vitamin B3, also called niacin, is another important nutrient that keeps your metabolism working, according to the NIH.

Niacin is involved in the conversion of nutrients into energy and the creation and repair of DNA. It's also said to have antioxidant effects, according to the Harvard School of Public Health.

The NIH reports that you may need more niacin in your diet if you:

• Are undernourished
• Have AIDS
• Have alcohol use disorder, anorexia, inflammatory bowel disease or liver cirrhosis
• Get too little iron, riboflavin or vitamin B6 (these are needed to convert tryptophan to niacin)
• Have Hartnup disease, a rare genetic disorder
• Have carcinoid syndrome, a condition where tumors develop in the gastrointestinal tract

If you don't get enough niacin, you may also come down with a condition called pellagra, which is characterized by diarrhea, dementia and dermatitis, according to the NIH.

Some other symptoms of niacin deficiency include:

• Rough skin
• A bright red tongue
• Vomiting, constipation or diarrhea
• Depression
• Headaches
• Extreme tiredness
• Aggressive, paranoid or suicidal behavior
• Hallucinations, apathy or loss of memory

According to the NIH, niacin may help:

• Metabolism
• Convert nutrients into energy
• Create and repair DNA
• Improve blood cholesterol levels (lowering "bad" LDL cholesterol and raising "good" HDL cholesterol)
• Protect against Alzheimer's and cognitive decline

The two most common forms of niacin in food and supplements are nicotinic acid and nicotinamide, and the body can convert the amino acid tryptophan into nicotinamide, according to the NIH.

If you get enough protein in your diet, you probably have enough niacin. Foods high in niacin include:

• Poultry
• Beef
• Pork
• Fish
• Nuts
• Enriched grains
• Legumes
• Milk
• Coffee
• Tea

The RDA for niacin is measured in milligrams NE, which stands for niacin equivalents, because your body makes niacin from tryptophan.

The recommended dietary allowance (RDA) of niacin, according to the NIH, is:

• ‌Adults assigned male at birth:‌ 16 milligrams NE
• ‌Adults assigned female at birth:‌ 14 milligrams NE
• ‌Pregnant people:‌ 18 milligrams NE
• ‌People who are lactating:‌ 17 milligrams NE

Even though niacin is water-soluble like the other B vitamins, there have been reports of overdose from supplements. According to the Harvard School of Public Health, excess niacin may cause:

• Temporary skin flushing
• Stomachache
• Diarrhea

Vitamin B5, also known as pantothenic acid, is another B vitamin that helps you metabolize carbohydrates, fat and protein. It's especially important for making and breaking down fats, per the NIH.

Because there are so many foods high in pantothenic acid, deficiency is extremely rare, per the NIH. But if a person is not getting enough nutrients in their diet, the Harvard School of Public Health reports that they might experience:

• Numbness in the hands and feet
• Headache
• Fatigue
• Irritability
• Gastrointestinal issues

According to the NIH, vitamin B5 may help:

• Carbohydrate, fat and protein metabolism
• Improve blood cholesterol and triglyceride levels

Almost all plant and animal foods have some pantothenic acid, but foods you can get most of your daily needs from include:

• Shiitake mushrooms
• Beef
• Tuna
• Chicken
• Organ meats
• Yogurt
• Potatoes
• Brown rice
• Avocados
• Sunflower seeds
• Fortified foods

The recommended dietary allowance (RDA) of pantothenic acid, according to the NIH, is:

• ‌Adults assigned male at birth:‌ 5 milligrams
• ‌Adults assigned female at birth:‌ 5 milligrams
• ‌Pregnant people:‌ 6 milligrams
• ‌People who are lactating:‌ 7 milligrams

There are no known side effects of pantothenic acid from food, but extremely high doses from supplements can cause diarrhea or water retention, per the Harvard School of Public Health

You need vitamin B6, sometimes called pyroxidine, for amino acid metabolism, according to the NIH. This is how protein from the food you eat gets broken down into amino acids, which your body then uses to make cells, muscles and other tissue.

During strenuous exercise, vitamin B6 speeds up the release of glucose from glycogen in your muscles. B6 helps your body form an iron-containing compound called heme, which gives your blood the ability to carry oxygen.

You also need this B vitamin to help convert tryptophan to niacin, which is just one example of how B vitamins work together to keep you healthy.

Vitamin B6 regulates the brain's levels of the mood-controlling neurotransmitters serotonin and dopamine, according to the NIH. It's also involved in brain development during pregnancy and infancy, and is important for a functioning immune system.

Symptoms of a vitamin B6 deficiency include:

• Weakness
• Skin inflammation
• Poor nerve function

According to the NIH, vitamin B6 may help:

• Amino acid metabolism
• Speed up the release of glucose from glycogen in your muscles during exercise
• Stabilize the neurotransmitters serotonin and dopamine in the brain
• Improve memory in older adults
• Lessen symptoms of PMS such as moodiness, irritability, forgetfulness, bloating and anxiety

The American Congress of Obstetricians and Gynecologists (ACOG) also recommends taking vitamin B6 supplements under a doctor's supervision for nausea and vomiting during pregnancy.

You can get vitamin B6 in your diet from sources like:

• Chicken
• Pork
• Legumes
• Fish
• Eggs
• Fortified cereals

The recommended dietary allowance (RDA) of pyroxidine, according to the NIH, is:

• ‌All adults age 19 to 50:‌ 1.3 milligrams
• ‌Adults assigned male at birth over 50:‌ 1.7 milligrams
• ‌Adults assigned female at birth over 50:‌ 1.5 milligrams
• ‌Pregnant people:‌ 1.9 milligrams
• ‌People who are lactating:‌ 2 milligrams

High doses of vitamin B6 given over long periods of time may result in painful neurological symptoms known as sensory neuropathy, per the NIH. People do not often get too much vitamin B6 from food.

Biotin, another important B vitamin sometimes referred to as vitamin H, is important for lipid and protein metabolism, according to the NIH. It also aids in gluconeogenesis, or the process of forming glucose, which your body — especially your brain — uses for energy.

Biotin supplements are often promoted to improve the health of your hair, skin, and nails, but the NIH reports that there is little evidence to back this up. Deficiency is rare, but could cause:

• Thinning hair on the head and body
• A rash around the eyes, nose, mouth and anal area
• Pinkeye
• High levels of acid in the blood and urine
• Seizures
• Skin infection
• Brittle nails
• Nervous system disorders

Bacteria in the gut can produce this nutrient, per the NIH. How much is produced varies from person to person, so it's still an essential vitamin to get from your diet. People at a higher risk for biotin deficiency include those who:

• Have a rare genetic disorder called "biotinidase deficiency"
• Have alcohol use disorder
• Are pregnant or breastfeeding

According to the NIH, biotin helps with:

• Fat and protein metabolism
• Production of glucose, which the brain uses for energy

You can meet your daily needs by eating foods high in biotin, like:

• Fish and meat
• Egg yolks
• Peanut butter
• Yeast

The recommended dietary allowance (RDA) of biotin, according to the NIH, is:

• ‌All adults, including pregnant people:‌ 30 micrograms
• ‌People who are lactating:‌ 35 micrograms

Vitamin B9, which is better known as folate or folic acid, is one of the most important nutrients to have during pregnancy.

"Folate" refers to the B vitamin that occurs naturally in food, and "folic acid" is the synthetic form found in supplements, according to the NIH.

The body uses folate to make DNA and other genetic material. The nutrient is also involved in the metabolism of protein and in keeping your blood healthy.

During pregnancy, it's also essential in forming the fetus' neural tube from which the brain and spinal cord develop.

Pregnant people who are deficient in folate run the risk of having babies born with defects that affect the head and spine, such as spina bifida or anencephaly. For others, folate deficiency can also cause:

• Poor growth
• Gingivitis
• Diarrhea
• Loss of appetite
• Forgetfulness
• Irritability

Low levels of folate are fairly common. Risk factors for deficiency include:

• Alcohol use disorder
• Inflammatory bowel disease
• Celiac disease

According to the NIH, folate helps with:

• Protein metabolism
• Cell division
• Creation of DNA and other genetic materials
• Neural tube development during pregnancy

Foods high in folate include:

• Liver
• Lentils
• Spinach
• Asparagus
• Brussels sprouts
• Broccoli
• Oranges
• Rice
• Peas

The recommended dietary allowance (RDA) of folate, according to the NIH, is:

• ‌All adults over age 19:‌ 400 micrograms
• ‌Pregnant people:‌ 600 micrograms
• ‌People who are lactating:‌ 500 micrograms

Taking too much folic acid through supplements may hide a vitamin B12 deficiency, per the NIH. Increasing folate may correct the anemia that comes along with vitamin B12 deficiency, but it will not stop the nerve damage that B12 deficiency also causes.

High doses of folate may also:

• Worsen symptoms of B12 deficiency
• Impair your immune system

Vitamin B12, also known as cobalamin, is used in protein and lipid (or fat) metabolism and in the synthesis of hemoglobin, according to the NIH. B12 helps make and maintain the outer covering of nerve fibers, which protect them from damage.

The body stores B12 in the liver, but even so, deficiency is common, per the NIH. A B12 deficiency can happen when the body has difficulty absorbing B12 from food especially as it ages, making deficiency more common in older adults.

A B12 deficiency can cause anemia or certain neurological issues, and it may even affect cognition by reducing the brain's total volume, according to a July 2019 study in ‌Neurology‌. A lack of vitamin B12 was associated with poorer long-term memory and perceptual speed, the researchers found.

To absorb B12, you must produce a protein called intrinsic factor in your stomach, which most people do, per the NIH. In rare cases, some people do not produce intrinsic factor and could experience vitamin B12 deficiency symptoms like:

• Weak muscles
• Fatigue
• Pale skin
• Heart palpitations
• Loss of appetite
• Weight loss
• Infertility
• Depression
• Problems with balance
• Confusion
• Memory problems
• Numbness or tingling, signifying nerve damage

Production of intrinsic factor decreases as you age, so getting your B12 levels checked as you enter middle age and beyond is probably a good idea.

Vitamin B12 supplements are often marketed for improving energy and athletic performance, but no evidence suggests that this is true in people who are getting enough B12 from their diet, per the NIH.

According to the NIH, vitamin B12 may help with:

• Development and function of the central nervous system
• Protecting the nerves from damage
• Healthy formation of red blood cells
• DNA synthesis
• Preventing anemia

Animal meat and dairy products are the main food sources of B12, so deficiency is usually not an issue for people who eat animal products. People who are vegan or follow a plant-based diet should talk to their doctor to see if they could benefit from a B12 supplement. Foods high in vitamin B12 include:

• Fish, meat and poultry
• Milk and yogurt
• Clams
• Beef liver
• Nutritional yeast
• Some breakfast cereals

The recommended dietary allowance (RDA) of vitamin B12, according to the NIH, is:

• ‌All adults:‌ 2.4 micrograms
• ‌Pregnant people:‌ 2.6 micrograms
• ‌People who are lactating:‌ 2.8 micrograms

Vitamin B12 is not associated with any harmful side effects. That being said, the NIH reports that B12 supplements may interact with the following medications:

• Gastric acid inhibitors
  
• Metformin

People take vitamin B-complex supplements (which include all of the eight B vitamins) for various reasons. B-complex supplements may help reduce symptoms of stress and anxiety, according to a February 2016 review in ‌Nutrients‌.

Supplements should only be taken under a doctor's supervision. It's very difficult to reach vitamin toxicity of most of the B vitamins save for three: B6, folate and niacin.

B6 toxicity can cause nerve damage, resulting in burning, pain, numbness and sensitivity to sunlight, according to the NIH. Folate toxicity does not have any outward symptoms but may mask other B vitamin deficiencies. Niacin toxicity may cause skin flushing, nausea, vomiting and liver damage.

Because B12 is metabolized in the liver and its by-products are removed from the body by the kidneys, too much B12 may be dangerous for people with diabetes or who have kidney or liver problems, per the NIH.

High blood levels of vitamin b12 have been associated with reduced kidney function, according to February 2015 research in ‌BMC Nephrology‌. High levels of B12 have also been associated with liver damage, according to November 2012 research in ‌Clinica Chimica Acta‌.

The bottom line: If your diet is balanced and rich in fruits, vegetables, grains and lean proteins, you do not need to supplement with B vitamins.

If you're not sure if you're getting enough B vitamins from your diet, speak with your doctor about which supplement might be right for you.