Supplements

Everything You Need to Know About B-Complex: Benefits, Dosage, and Side Effects

Written by Robert Iafelice, MS, RDN, LDN
Medically Reviewed by Dr. Elaine Gavalas, ND, PhD

August 1, 2024

Health-conscious Americans have been supplementing with B-complex vitamins for several decades. A common reason is the belief that B vitamins can provide an energy boost and fight stress. But doesn’t our diet provide sufficient B vitamins? 

Not necessarily.

Although severe B vitamin deficiencies are uncommon in the U.S., there’s a good chance you aren't getting enough of one or more B vitamins (1). In fact, it’s been estimated that around half of the adult population in the U.S. and U.K. have insufficient levels of vitamin B12 (2).

A shortage of B vitamins can lead to physical and mental fatigue as well as an increased risk of chronic diseases and less than optimal brain function (3). 

Plenty of clinical evidence supports the idea that taking B-complex vitamins is a simple way to help boost your well-being, keep your mind sharp, and feel more energetic (3).

So, which vitamins make up the B-complex, and what are their roles in the body?

Table Of Contents

What is B-Complex?

While B vitamins don’t serve as fuel themselves, they play an essential role in extracting energy from food. They are also critical cofactors that assist enzymes in many metabolic pathways, including the synthesis of neurotransmitters, DNA, and RNA (4). 

There are eight members of the B-complex family (4):

1. Vitamin B1 (Thiamine)

Vitamin B1—also known as thiamine—helps the body's enzymes metabolize glucose into energy in the cell’s ‘power plants—known as mitochondria. A thiamine deficiency can cause nerve damage.

2. Vitamin B2 (Riboflavin)

Riboflavin plays a role in the metabolism of other B vitamins (niacin, B6, and folate) as well as iron. It also has antioxidant properties and is needed to produce glucose from carbohydrates, proteins, and fat.

3. Vitamin B3 (Niacin)

Niacin is a precursor to NAD and NADP—crucial molecules central to metabolism (particularly energy-producing reactions) and DNA repair. A niacin deficiency can also cause thick, scaly skin.

4. Vitamin B6 (Pyridoxine)

Vitamin B6 helps many of the enzymes involved in the metabolism of carbohydrates, proteins, and fats; it also supports immune function and brain health. 

5. Vitamin B5 (Pantothenic Acid)

Pantothenic acid plays a key role in Coenzyme A, which is needed for making fatty acids, cholesterol, hormones, and the neurotransmitter acetylcholine.

6. Vitamin B12 (Cobalamin)

Vitamin B12 is important for your body. It helps make red blood cells, builds genetic material like DNA and RNA, and keeps your central nervous system healthy. A deficiency in vitamin B12 can lead to anemia, fatigue, muscle weakness, intestinal problems, nerve damage, and mood disturbances.

7. Folate

Like B12, folate is vital for DNA/RNA synthesis and red blood cell production. Low folate during pregnancy increases the risk of birth defects.

8. Biotin

Biotin plays an important role in the metabolism of fatty acids, glucose, and amino acids. A biotin deficiency can adversely affect hair, nails, and skin.

5 Health Benefits of B-Complex

Given the important roles B vitamins play and the fact that many people don't get enough, it's no wonder that taking a B-complex supplement can offer some great health perks. Think brainpower, immunity, energy levels, and metabolism benefits!

1. Metabolic Health

According to data from the National Health and Nutrition Examination Survey, nearly 90% of adult Americans are metabolically unhealthy (5). People who are metabolically unhealthy aren't hitting the best levels for the five cardiometabolic risk factors that make up metabolic syndrome (also known as insulin resistance syndrome).

These include (5): 

When you're short on any B vitamin, it can disrupt how your body processes amino acids, glucose, and fatty acids in the mitochondria (4). When your mitochondria malfunction, it's linked to oxidative stress (free radical damage) and inflammation common in metabolic syndrome (6).

Higher intake and levels of folate, vitamin B6, and vitamin B12 have been associated with a lower incidence of metabolic syndrome and a lower risk of cardiovascular diseases (7, 8). 

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2. Natural Energy Levels

Having enough of each B vitamin—except folate—is crucial for your body's energy production. If you're running low on any of them, you can feel tired and sluggish. And nobody wants that, right? 

Low energy in your cells can even lead to cell death and, eventually, disease (3). So, it’s important to take a complete B complex with all 8 B vitamins to help maintain natural energy levels. 

Plus, certain B vitamins help move oxygen around your body. Not getting enough B6, B12, or folate can result in anemia, where you lack enough red blood cells to carry oxygen, leading to fatigue.(3). 

3. Brain Health

Most of the studies investigating the effects of B vitamins on brain function have been focused on elevated levels of homocysteine—an independent risk factor for several diseases, including:

  • Cognitive impairment
  • Alzheimer’s disease
  • Dementia

Homocysteine is an amino acid that gets produced in the body when we break down the essential amino acid methionine. A deficiency of vitamin B12, B6, or folate, can disrupt the natural breakdown of homocysteine, causing it to build up in your blood and lead to some toxic effects in your body. (1).

In a 2021 systematic review, supplementation with vitamins B6, B12, and folic acid in patients with mild cognitive impairment significantly decreased blood homocysteine levels after just one month (9). Since vitamins B2 and B3 also contribute to homocysteine metabolism, supplementation with the full B complex may be more effective than the use of only three of the B vitamin group (1).

Native Note: Since sufficient vitamin B12 and folate are especially vital for detoxifying homocysteine, the biologically active forms of these vitamins are more bioavailable and preferred. Thus, the best B-complex vitamins contain folate as 5-methyltetrahydrofolate (or 5-MTHF) and B12 as methylcobalamin (10, 11).

4. Immune Support

Your body needs to have enough micronutrients—including B vitamins—to keep the immune system strong. If you're low on B vitamins, your immune function might get weaker, making you more prone to infections. Taking B vitamin supplements can help support immune functions in people who are lacking them. (12).

Just like all the other cells in your body, the cells of your immune system can be damaged by free radicals. Vitamins B2, B3, B12, and folate act as antioxidants, providing support to your immune system by helping to protect immune cells from oxidative stress. (13). 

Vitamin B complex also has a role in helping to regulate immune responses as well as chronic inflammation, which is strongly linked to cancer development. Owing, in part, to their anti-inflammatory properties, some B vitamins (B2, B6, and folate) exert anti-tumor effects (14). 

Furthermore, the immune response against foreign invaders demands a great deal of energy (15). B-complex vitamins provide the necessary spark to burn fuel for energy in the cell’s mitochondria. 

5. Fetal Development

Folate requirements are increased during pregnancy to support the fetus's growth and development. A folate deficiency during pregnancy increases the risk of neural tube defects and other birth defects (16). 

Maternal intake of other B vitamins may protect against small for gestational age (SGA) newborns. Specifically, higher intakes of vitamins B1, B3, and B12 and moderate intakes of vitamin B6 and folate correlated with lower risk of SGA (17). 

Potential Side Effects of B-Complex

When taken at Recommended Daily Allowance (RDA) doses, B vitamins don’t typically cause adverse effects. Since any excess is eliminated via the urine, even doses much higher than the RDA are generally safe. However, a ceiling has been set for three B vitamins: vitamin B6, folate, and niacin (1).

Folic acid supplementation may also mask the underlying B12 deficiency, which, if left untreated, may lead to permanent nerve damage. That's why an upper limit of 1000 mcg/day was set for folate.

 An upper limit of 35 mg/day was ascribed for niacin because high doses can cause temporary but harmless flushing of the skin. Case reports of high doses of B6 (> 1000 mg/day) for prolonged periods causing reversible nerve damage prompted an upper limit of 100 mg/day to be established (1).

How Much Vitamin B-Complex Do You Need?

The RDA of each B vitamin varies. According to the National Institutes of Health (NIH), the recommended daily intake is (18):

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Your doctor or healthcare provider can provide dosage information tailored to your individual needs.

Who Can Benefit From Taking B-Complex?

As mentioned before, a lot of Americans don't get enough B vitamins from their diet alone. (1, 10). Considering that B complex vitamins are safe when taken at appropriate doses, everyone could benefit from taking a B-complex to fill in the gaps and ensure adequate levels in the body. 

Nevertheless, certain groups of people are at high risk of developing vitamin B deficiencies (19, 20, 21, 22) and would especially benefit from B-complex supplementation:

  • Alcoholics
  • Vegans
  • Elderly
  • Individuals with poor digestion or malabsorption
  • People with genetic disorders
  • People with intestinal diseases
  • Individuals on medications
  • Malnourished individuals
  • Those struggling with an eating disorder like anorexia or bulimia

Due to their ability to keep levels of toxic homocysteine in check, B-complex supplementation may be a helpful preventative measure to take for people at risk for cardiovascular disease, metabolic syndrome, cognitive impairment, and Alzheimer’s disease (1, 7, 8). 

How to Incorporate Your B-Complex Into Your Routine

It’s best to follow the label instructions on your B-complex (23). Nevertheless, B-complex is typically taken with food since B vitamins generally function as catalysts that spark the burning of food for energy. 

Since B vitamins are water-soluble and generally don’t last long in the body, taking them in divided doses with food is ideal…but not necessary. If the product is designed as a one-per-day, then it's best to take it early in the day.

The Bottom Line

Food processing, soil depletion, aging, drug interactions, poor food choices, and chronic stress …all of these factors can contribute to the high prevalence of vitamin B deficiencies. 

The B vitamins play many crucial roles in your body. A deficiency in any of them can lead to physical and mental fatigue, cognitive decline, and an increased risk of chronic diseases. 

Perhaps most importantly, B vitamins help keep levels of potentially toxic homocysteine under control. A growing body of research suggests that high homocysteine levels may raise the risk of many of today’s killer diseases, including heart disease and Alzheimer’s disease.

Adding a high-quality complete B-complex supplement to your routine is an easy way to help fill in the gaps, support your energy levels, and potentially reduce the risk of serious diseases.

Robert Iafelice
Article by

Robert Iafelice

Robert Iafelice, MS, RD, LDN is a functional nutritionist and freelance medical writer. He is the author of Hold On to Your Muscle, Be Free of Disease, a unique perspective on wellness and disease in the context of muscle health.

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    Medical Disclaimer

    This content is for informational and educational purposes only. It is not intended to provide medical advice or to take the place of such advice or treatment from a personal physician. All readers/viewers of this content are advised to consult their doctors or qualified health professionals regarding specific health questions. Neither Dr. Chad Walding nor the publisher of this content takes responsibility for possible health consequences of any person or persons reading or following the information in this educational content. All viewers of this content, especially those taking prescription or over-the-counter medications, should consult their physicians before beginning any nutrition, supplement, or lifestyle program.

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