Vitamin B Complex: Benefits, Side Effects, and Dosage

B complex vitamins usually deliver eight of the B vitamins: B1 (thiamin), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate), and B12 (cobalamin). Found naturally in meat, leafy greens, dairy, beans, peas, and whole or fortified grains, B complex vitamins are water-soluble and play an essential role in certain bodily functions including helping your body make energy from the food you eat and forming red blood cells.

benefits of B vitamins — Verywell / Joshua Seong

Health Benefits

Each of the eight vitamins in vitamin B complex supplements comes with its own unique set of health benefits. For instance, vitamin B1 is critical for the growth, development, and function of cells in the body. Other vitamins, such as B2, work cooperatively in the body with other B vitamins to convert food into energy. B2 converts B6 into a usable form and aids in niacin production.

Vitamin B5 breaks down fats and carbohydrates for energy and helps the body use other vitamins, such as riboflavin (found in B2). B6 is involved in immune function and needed by the body to use and store protein and carbohydrates from food in the form of glycogen.

B7 also helps the body convert the fats, carbohydrates, and proteins in the food you eat into energy. It is needed to make fatty acids and also maintains bone and hair health. Vitamin B9 is required to help cells produce and maintain DNA (the genetic material found in all body cells), while B12 is important for protein metabolism.

Not everyone requires vitamin B supplementation. Depending on your individual needs and recommendations from your doctor, you may be advised to take a specific B vitamin supplement alone over a B-complex supplement.

Converts Food Into Energy

Most of the B vitamins are involved in the process of converting food into energy. Some help metabolize carbohydrates, while others break down fat and/or protein.

While this is an essential process, it is not necessarily the case that taking a B-complex supplement will make you feel more energetic. Although your body needs B vitamins to create energy from the foods you eat, the effect is different when these vitamins are consumed in the form of dietary supplements rather than food.

B vitamins involved: B1, B2, B3, B5, B6, B7, and B12

Supports Brain Health

Research shows that B vitamins support just about every aspect of brain health. While all B vitamins promote healthy brain function, a 2016 review published in Nutrients indicates that vitamins B6, B9, and B12 play a particular role in homocysteine metabolism, which helps reduce the risk of cognitive decline and dementia. In particular, B12 supports healthy DNA structures, which are important during fetal development and the prevention of chronic disease and cancer.

Vitamin B6 supports both brain development and function, while vitamin B9 reduces the risk of birth defects in the brain and spine, such as spina bifida.

B vitamins involved: B1, B2, B3, B5, B6, B7, B9, B12

Produces Red Blood Cells

Some B vitamins, particularly vitamin B12, play an essential role in red blood cell formation. Healthy red blood cells are needed to transport oxygen to every part of the body. When there is a vitamin B12 deficiency, the body cannot produce enough red blood cells and anemia can occur.

Vitamin B2 is also needed for red blood cell production and growth, as is vitamin B9. While vitamin B5 plays a role in red blood cell production, it also helps reduce the amount of cholesterol produced by the body. And vitamin B6, which is required for more than 100 different enzyme reactions in the body, aids in the formation of hemoglobin, which also allows red blood cells to carry oxygen through the blood.

B vitamins involved: B2, B5, B6, B9, B12

Promotes Nervous System Health

Vitamin B2 keeps the eyes, nervous system, and skin healthy. It aids in the conversion of food into energy and helps enzymes in the body function properly. It also makes and repairs DNA, helps with the optimal function of the digestive and nervous systems, and promotes skin health. In addition, vitamin B12 also plays a role in maintaining the health of the nervous system.

B vitamins involved: B1, B2, B3, B6, B12

Supports Hormone Production

Vitamins B3 and B5 are needed for the production of hormones in the adrenal glands, such as sex and stress hormones. Vitamin B6 stimulates neurotransmitters and hormones that influence mood and regulate the body's biological clock.

B vitamins involved: B3, B5, B6

May Reduce Stress

Research shows that certain B vitamins may help to alleviate stress. For instance, a 2019 study published in Nutrients determined that vitamin B supplementation can benefit mood, though more research on the dietary patterns and micronutrient statuses of broader populations is still needed to make an evidence-based recommendation.

B vitamins involved: B1, B2, B3, B5, B6, B7, B9, B12

May Prevent Migraines

Vitamin B supplementations may also help prevent migraines in some people. A 2015 report looked at the effects of vitamin B supplementation on individuals with migraines. The authors determined that reducing homocysteine levels with folic acid (the synthetic form of folate) and vitamins B6 and B12 may help reduce symptoms associated with migraine with aura, which is a recurring headache with sensory disturbances.

However, the report notes that more rigorous research is still needed to determine the safety and efficacy of B vitamin supplementation as a preventative measure for people with chronic migraine headaches.

B vitamins involved: B2, B6, B9, B12

Dosage

While most people who eat a varied diet get enough B vitamins from food, some people are at an increased risk of deficiency, particularly those who are over the age of 50, take antacid medication, or have celiac disease, Crohn's disease, gastritis, or other digestive disorders.

If you have had stomach or weight loss surgery, drink alcohol regularly, or follow a vegetarian or vegan diet, you may also be more prone to a deficiency. People who are pregnant or breastfeeding may need more vitamins B6, B12, and folate.

The National Institutes of Health (NIH) provides the following recommended daily intakes (RDI) for each of the eight B vitamins

Recommended Daily Intakes (RDIs) for B Vitamins
	Men	Women
B1 (Thiamin)	1.2 mg	1.1 mg
B2 (Riboflavin)	1.3 mg	1.1 mg
B3 (Niacin)	16 mg	14 mg
B5 (Pantothenic acid)	5 mg	5 mg
B6 (Pyridoxine)	1.3 mg	1.3 mg
B7 (Biotin)	30 mcg	30 mcg
B9 (Folate)	400 mcg	400 mcg
B12 (Cobalamin)	2.4 mcg	2.4 mcg

Maintaining your RDI for B vitamins can help prevent deficiencies. Depending on which B vitamin(s) you are deficient in, symptoms may include any of the following:

Anemia
Brittle hair and nails
Cardiovascular symptoms
Depression
Difficulty concentrating
Fatigue
Hair loss
Irritability
Nervousness
Short-term memory loss
Skin disorders
Upset stomach
Weakness
Weight loss

Possible Side Effects

Although B complex supplements are water-soluble and do not stay in the body for long, large doses of the vitamins in supplement form can cause certain side effects. There is a daily tolerable intake level (UL) for some B vitamins (which is above what most people need) but it is not established for all the B vitamins.

For example, the RDA for thiamin (vitamin B1) is 1.2mg. There is no tolerable upper limit for this because there have been no adverse effects recorded at intakes above 50 mg but that doesn't mean that there can't be. The tolerable upper limit for niacin (vitamin B3) is 35mg, for vitamin B6 is 100mg, and for vitamin B9 (folate) is 1000mcg.

Before starting any supplement, you should consult with your healthcare provider.

Getting more than the UL increases your chances of side effects such as the following:

B3 (niacin): Excess B3 may cause skin flushing or pain, elevated blood sugar levels, and liver toxicity.
B6 (pyridoxine): B6 may cause nerve damage, skin lesions, worsening of kidney function, and increased risk of heart attack, stroke, and death in people with diabetes and advanced kidney disease. Studies have associated high doses of vitamin B6 with a slightly increased risk of hip fracture and increased risk of lung cancer (when taken with vitamin B12).
B9 (folate): Vitamin B6 can result in kidney damage, increased insulin resistance in offspring, lower natural killer cell activity in older women, and may be associated with an increased risk of some cancers. It also may mask the diagnosis of a vitamin B12 deficiency.
B12 (cobalamin): Vitamin B12 has been found to speed the decline in kidney function and increase the risk of cardiovascular events in people with impaired kidney function. High doses of vitamin B12 taken with folic acid have been associated with a greater risk of cancer and mortality, along with acne and rosacea in some people.

What to Look For

In the United States, dietary supplements are not held to the same rigorous testing standards as pharmaceutical drugs. This means that the quality of supplements like B vitamins may vary from one brand to the next.

When shopping for vitamin B supplements, look for brands that have been tested by an independent certification organization such as the U.S. Pharmacopeia (USP), ConsumerLab, or NSF International. This can help to ensure quality.

You can find many different brands of vitamin B supplements at drug stores, grocery stores, health food shops, and online. Vitamin B supplements should be stored in a cool, dry place and out of reach of children.

Dietary Sources of B Vitamins

B vitamins are found primarily in animal food sources and fortified cereals. But many vegetables, fruits, nuts, and legumes contain some amount of B vitamins as well. Here's a look at the common food sources. You'll note that many of the foods overlap with other B vitamins.

B1 (thiamin): Fortified breakfast cereal, enriched and whole-grain products (bread, breakfast cereals, rice, noodles, and flour), wheat germ, pork, trout, black beans, mussels, and tuna
B2 (riboflavin): Milk and dairy products, fortified breakfast cereals, beef liver, clams, portobello mushrooms, almonds, and chicken
B3 (niacin): Eggs, fish, fortified bread and cereal, rice, nuts, milk and dairy, chicken, beef, turkey, lamb, organ meats, peanuts
B5 (pantothenic acid): Meat, avocado, broccoli, kale, eggs, milk, mushrooms, fortified cereals, organ meats, poultry, potatoes, and legumes
B6 (pyridoxine): Chickpeas, beef liver, tuna, salmon, chicken breast, fortified breakfast cereal, potatoes, turkey, fruits (except citrus), and beef
B7 (biotin): Beef liver, egg yolk, wheat germ, pork, beef, sunflower seeds, sweet potato, almonds, whole-grain foods, sardines, spinach, and broccoli
B9 (folate): Spinach, beef liver, broccoli, Brussels sprouts, beans and legumes, asparagus, orange juice, peanuts, avocado, dark leafy greens, fortified cereals, and salmon

B12 (cobalamin): Beef liver (and other organ meats), clams and other shellfish, beef, chicken, fish, eggs, milk and other dairy products, and some fortified cereals

A Word From Verywell

To stay healthy, most people can get what they need by eating a varied, balanced diet filled with foods naturally rich in B vitamins, such as leafy greens, nuts, beans and legumes, whole grains, lean protein, mushrooms, and eggs. There isn't solid evidence to support taking excessive amounts of B vitamins if you're not deficient in them.

If you're not getting enough of a B vitamin from your diet, taking a vitamin B supplement may be beneficial. Deficiency in B vitamins can cause a number of symptoms, including tiredness, anemia, loss of appetite, depression, abdominal pain, muscle cramps, hair loss, and eczema. Consult your healthcare provider to find out whether a B complex supplement is right for you.