B-Complex Vitamins: Benefits, Side Effects and Dosage


B vitamins are a group of nutrients that play many important roles in your body.

Most people get the recommended amounts of these vitamins through diet alone since they are found in a wide variety of foods.

However, factors like age, pregnancy, dietary choices, medical conditions, genetics, medication and alcohol use increase the body’s demand for B vitamins.

In these circumstances, supplementing with B vitamins may be necessary.

Nutritional supplements that contain all eight B vitamins are referred to as B-complex vitamins.

Here are the health benefits of B-complex vitamins as well as dosage recommendations and potential side effects.

B-complex supplements usually pack all eight B vitamins into one pill.

B vitamins are water-soluble, which means your body does not store them. For this reason, your diet must supply them each day.

B vitamins have many important functions and are vital for maintaining good health.

B-complex vitamins usually contain the following:

  • B1 (thiamine): Thiamine plays an essential role in metabolism by helping convert nutrients into energy. The richest food sources include pork, sunflower seeds and wheat germ (1).
  • B2 (riboflavin): Riboflavin helps convert food into energy and also acts as an antioxidant. Foods highest in riboflavin include organ meats, beef and mushrooms (2).
  • B3 (niacin): Niacin plays a role in cellular signaling, metabolism and DNA production and repair. Food sources include chicken, tuna and lentils (3).
  • B5 (pantothenic acid): Like other B vitamins, pantothenic acid helps your body obtain energy from food and is also involved in hormone and cholesterol production. Liver, fish, yogurt and avocado are all good sources (4).
  • B6 (pyridoxine): Pyridoxine is involved in amino acid metabolism, red blood cell production and the creation of neurotransmitters. Foods highest in this vitamin include chickpeas, salmon and potatoes (5).
  • B7 (biotin): Biotin is essential for carbohydrate and fat metabolism and regulates gene expression. Yeast, eggs, salmon, cheese and liver are among the best food sources of biotin (6).
  • B9 (folate): Folate is needed for cell growth, amino acid metabolism, the formation of red and white blood cells and proper cell division. It can be found in foods like leafy greens, liver and beans or in supplements as folic acid (7).
  • B12 (cobalamin): Perhaps the most well-known of all the B vitamins, B12 is vital for neurological function, DNA production and red blood cell development. B12 is found naturally in animal sources like meats, eggs, seafood and dairy (8).

Although these vitamins share some characteristics, they all have unique functions and are needed in different amounts.


B-complex supplements usually contain all eight B vitamins conveniently packed into one pill.

Since B vitamins are found in many foods, you are most likely not at risk of developing a deficiency as long as you follow a well-rounded diet.

However, certain circumstances increase the need for B vitamins, making supplements necessary.

Pregnant or Breastfeeding Women

During pregnancy, the demand for B vitamins, particularly B12 and folate, grows to support fetal development (9).

In women who are pregnant or breastfeeding, especially those who follow vegetarian or vegan diets, supplementing with a B-complex vitamin is crucial.

B12 or folate deficiency in pregnant or breastfeeding women can lead to severe neurological damage or birth defects in the fetus or infant (10).

Older Adults

As you age, your ability to absorb vitamin B12 decreases and your appetite declines, making it difficult for some people to get enough B12 through diet alone.

The body’s ability to release B12 from food so that it can be absorbed depends on adequate amounts of stomach acid.

However, it’s estimated that 10–30% of people over 50 don’t produce enough stomach acid to properly absorb B12 (11).

Deficiency in B12 has been linked to increased rates of depression and mood disturbances in elderly people (12, 13).

Deficiencies in vitamin B6 and folate are also common in the elderly population (14, 15).

Those With Certain Medical Conditions

People with certain medical conditions, such as celiac disease, cancer, Crohn’s disease, alcoholism, hypothyroidism and anorexia, are more susceptible to developing nutrient deficiencies, including B vitamins (16, 17, 18, 19, 20).

Additionally, the MTHFR genetic mutation can affect how your body metabolizes folate and can lead to a folate deficiency and other health issues (21).

What’s more, people who have undergone certain weight-loss surgeries are also more likely to be deficient in B vitamins (22).

In these circumstances, patients are often advised to supplement with a B-complex vitamin to correct or avoid deficiencies.

Vegetarians and Vegans

Vitamin B12 is naturally found in animal products like meat, dairy, eggs and seafood.

Vegans and strict vegetarians could be at risk of developing a B12 deficiency if they don’t get enough of this vitamin through fortified foods or supplements (23).

A daily B-complex vitamin can help ensure that people who choose to follow diets that eliminate animal products are getting enough of these important nutrients.

People Taking Certain Medications

Commonly prescribed medications can lead to a deficiency in B vitamins.

For example, proton pump inhibitors, which are medications that lower stomach acid, can decrease the absorption of B12, while metformin, a popular diabetes drug, can decrease levels of both B12 and folate (24, 25).

Birth control pills can also deplete several B vitamins, including B6, B12, folate and riboflavin (26).


Pregnancy, medical conditions, surgeries, genetic mutations, medications, dietary restriction and age can all affect how your body absorbs and uses B vitamins.

While certain conditions make it necessary for some people to supplement with B-complex vitamins, research has shown that taking a B-complex supplement may be helpful even for people who don’t have an increased need for these nutrients.

May Reduce Stress and Boost Mood

B-complex vitamins are often used to reduce fatigue and boost mood.

Some studies suggest that B-complex vitamins can lift your spirits and improve your cognitive performance.

A 33-day study in 215 healthy men found that treatment with a high-dose B-complex and mineral supplement improved general mental health and stress and enhanced performance on cognitive tests (27).

Another study in young adults showed that supplementing with a multivitamin containing high levels of B-complex vitamins for 90 days reduced stress and mental fatigue (28).

May Reduce Symptoms of Anxiety or Depression

While B-complex vitamin supplements are not a cure for mental health issues, they may help improve symptoms of depression or anxiety.

A study in 60 adults with depression showed that treatment with a B-complex vitamin for 60 days led to significant improvements in depression and anxiety symptoms, compared to a placebo (29).

B vitamins may also enhance treatment response when given in combination with antidepressant medication.

One study found that supplementing patients with a vitamin containing B12, B6 and folic acid led to a more enhanced and sustained antidepressant response over one year, compared to a placebo (30).

Note that low blood levels of certain B vitamins, including B12, B6 and folate, have been linked to an increased risk of depression, which is why it’s important to rule out nutrient deficiencies if you are experiencing symptoms of depression (31, 32).


B-complex supplements may relieve stress, boost cognitive performance and reduce symptoms of depression and anxiety, even in people without B vitamin deficiencies.

Each B vitamin has a specific recommended daily amount that varies depending on gender, age and other variables like pregnancy.

For women and men, the recommended daily intake (RDI) for B vitamins are as follows:

Pregnant and lactating women need higher amounts of B vitamins, while infants and children need less (33).

If you are deficient in B vitamins, you may need to supplement with higher doses to correct the deficiency.

For these reasons, it’s important to choose a B-complex supplement based on your individual requirements for each B vitamin.

Speak with your doctor regarding your specific nutrient needs based on your age and health.


Recommended intake for B vitamins varies depending on age, nutrient demands, gender and health status.

Since B vitamins are water-soluble, it’s unlikely that you will consume too much of these nutrients through diet alone or by taking a B-complex supplement as directed.

However, taking supplements that contain excessively high and unnecessary quantities of B-complex vitamins could lead to serious side effects.

High doses of supplemental B3 (niacin) may lead to vomiting, high blood sugar levels, skin flushing and even liver damage (34).

Additionally, high doses of B6 can cause nerve damage, light sensitivity and painful skin lesions (35).

Another side effect of B-complex supplements is that it can turn urine bright yellow.

Although discolored urine can be shocking, it’s not dangerous but simply your body getting rid of excess vitamins that it can’t use.

If you need to take a B-complex supplement, always choose reputable brands that volunteer to have their products independently tested by organizations like the US Pharmacopeial Convention (USP).


Although taking B-complex supplements as directed is likely safe, consuming high doses of B3 or B6 can lead to serious side effects.

Pregnant women, older adults, vegans and those with certain medical conditions may benefit from taking a B-complex supplement.

Taking these supplements may also improve mood, cognitive function and symptoms of depression.

Side effects are unlikely if you follow the recommended dosage, which varies depending on age, nutrient demands, gender and health.

If you aren’t sure if taking a B-complex supplement will benefit your health, speak with your doctor to help you determine if it’s the right choice for you.

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