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B-Complex: Benefits & Uses

Last Updated: April 19, 2022

Overview | Benefits | Physical Symptoms of Deficiency | Mental Symptoms of Deficiency | Dosage | Side effects | Buyers Guide | The bottom line

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B vitamins are found in a variety of foods and play a number of important roles in your body.

Most people get adequate amounts of B vitamins from their diet.

However those who are deficient may have great benefits from supplementation.

What are B-Complex Vitamins?

There are 8 B vitamins that make up the B-complex vitamins.

  • thiamine (B-1)
  • riboflavin (B-2)
  • niacin (B-3)
  • panthothenic acid (B-5)
  • pyridoxine (B-6)
  • biotin (B-7)
  • folate (B-9)
  • B-12 also known as cobalamin

When you body detects high levels of B-vitamins, they are excreted in the urine as B vitamins are water soluble.

Benefits of B-Vitamins

B Vitamins contribute to energy production and are crucial in the maintenance of our well-being. For those who are deficient, replenishing B-Vitamin levels to normal amounts will improve vitality and mood.

  • B1 (Thiamine) helps us to utilise the energy from food efficiently.
  • B2 (Riboflavin) helps convert the food we eat into energy whilst also working as an antioxidant.
  • B3 (niacin) allows our cells to convert food into useful energy. B3 deficiency is rare.
  • B5 (panthothenic acid) helps our body to burn fat and is vital for energy production.
  • B6 or pyridoxine performs a wide range of functions such as protein metabolism for muscle gain and breakdown.
  • B7 (Biotin) is stored in the liver and speeds up nutrient metabolism.
  • B9 or folate is responsible for DNA and genetic material in the body.
  • B12 (cobalamin) is responsible for healthy red blood cell production and helps make DNA in your cells.

Despite their myriad benefits for physical health, the role of B complex vitamins on our brain function is not well understood [1].

However there is evidence that B-vitamins play a role in brain health.

This is because deficiencies can lead to measurable changes in the brain.

In fact, biotin is found in the brain at concentrations 50 times that seen in blood [2].

B-Vitamins are involved in reducing homocysteine levels, which have been associated with heightened Alzheimer’s risk.

Physical Symptoms of Vitamin B Deficiency

Whilst B-vitamins work together and therefore exhibit similar deficiencies – there are certain signs that may indicate a specific deficiency.

  • B1 deficiency can lead to mild symptoms general fatigue, weakness and gastro-intestinal symptoms. Further deficiency can lead to peripheral nerve damage, cardiovascular dysfunction leading to pain, impaired sensory perception, swelling, shortness of breath, irregular heart rate, and heart failure.
  • B2 deficiency is extremely rare. It may result in angular cheilitis, cracked lips, dry skin, angular stomatitis (lesions at the corner of the mouth), hair loss, reproductive problems, sore throat ,red itchy eyes and . Deficiency in B2 can lead to decreased metabolism of folate and B-6 [x].
  • B3 deficiency is rare. However dermatitis, muscle weakness, burning in extremities, altered gait and gastrointestinal disorders are symptoms [3]. Those at risk of niacin deficiency include people who suffer from gastrointestinal disorders of the small intestine. Those who have excessive and chronic alcohol intake are also at risk of Niacin deficiency because alcohol reduces niacin absorption [4].
  • B5 deficiency may result in anemia, susceptibility to infections, fatty liver, adrenal dysfunction, muscle spasms, neuropathy, hypoglycemia, inflammation, dermatitis and impaired wound healing.
  • B6 deficiency can lead to anaemia, scaly skin on the lips, cracks in the mouth and a swollen tongue. Other symptoms can include a weakened immune system. Children can become irritable or develop sensitive hearing or seizures. [5]
  • B7 deficiency may cause increases in peripheral neuropathy (burning in your hands/feet), brittle nails and eczema [6]. Those at risk of biotin deficiency include people with alcohol dependence and those who have biotinidase deficiency – a rare genetic disorder.
  • B9 deficiency can lead to peripheral neuropathy, anaemia, spinal cord lesions and metabolic abnormalities. B9 deficiency is almost always accompanied with other nutrient deficiencies. Early stage deficiency manifests as weakness, fatigue, difficulty concentrating, irritability and shortness of breath. Those who have a poor diet, alcoholism and malabsorptive disorders such as IBS are at risk of B9 deficiency. Folate deficiency is more common in pregnant women. Women with insufficient folate are at increased risk of giving birth to infants with neural tube defects, low infant birth weight, preterm delivery and growth retardation.
  • B12 deficiency results in anaemia, peripheral neuropathy, spinal cord lesions, metabolic disorder, fatigue, pale skin, dementia, weight loss and infertility. Pregnant women deficient in B12 can cause anemia, neural tube defects and low birth weight in their children.

Mental Symptoms of Deficiency

The mental symptoms of B-vitamin deficiency are largely to do with feelings of anxiety and unpredictable behaviour.

  • B1 (Thiamine): Mild deficiency can lead to irritability, emotional disturbance, confusion, sleep problems and memory loss [7]. Further deficiency can lead to Wernicke-Korsakoff syndrome (neurodegeneration). This can lead to ataxia (uncoordination), abnormal motor function and eye movement, amnesia and apathy [8].
  • B2 (Riboflavin): Deficiency can lead to issues with memory, fatigue, personality changes [9].
  • B3 (Niacin): Mental symptoms of deficiency include anxiety, vertigo, memory loss, psychosis, aggression, paranoia and depression. Those who abuse alcohol are at risk of niacin deficiency – something to keep in mind during coronavirus lockdown.
  • B5 (Pantothenic acid): Deficiency in B-5 can lead to behaviour change, physical changes in the brain (encephalopathy) that affect how you think. It can also lead to nerve demyelination which can cause neuropathy.
  • B6: Deficiency can lead to depression, impaired attention, mental decline, dementia, nerve damage, convulsions and impaired alertness [10].
  • B7 (Biotin): Depression, lethargy, hallucinations and seizures [11]. More prevalent in those suffering from poor blood sugar control and type II diabetes.
  • B9 (Folate): Symptoms of deficiency include affective disorders, psychosis, behaviour changes, mental decline, dementia (including vascular dementia) and Alzheimer’s disease [12].
  • B12 (Cobalamin): Mental symptoms of deficiency are similar to folate deficiency and include altered mental wellbeing, psychosis, behaviour changes, cognitive decline and dementia.


RDA (recommended daily intakes):

  • B1: 1.2 mg/d for adult males, 1.1mg/d for adult women, children slightly less around 0.6-1.2 mg/day
  • B2:  1-1.3 mg/d for adults
  • B3: 16 mg/day for adult males, 14mg/day for adult women, 17mg for lactating women/day, 18mg/day for pregnant women
  • B5: 5 mg/day for adults, kids slightly less (2-4mg)
  • B6: 1.7 mg/day for adults, kids slightly less (1-1.6mg)
  • B7: 30 mcg/day for adults
  • B9: 400 mcg for adults, 600mcg pregnant women , lactating women 500 mcg, children 200-400 mcg
  • B12: 1.8 mcg for adults, 2.3 mcg for pregnant women

These conservative limits are enough to prevent deficiency however athletes or those in situations that are stressful may require higher levels of supplementation.

Buyers Guide

Reminder that most people consume more than enough B vitamins in their diet, and food sources are plentiful. However there are certain people that can benefit from supplementation.

Taking a B-complex is the best way to supplement as there is a synergistic effect. Please look out for a few things on the label when researching;

  • B1: B1 is in fortified foods such as black beans, tuna, trout, yoghurt.
  • B3: Niacin should not be supplemented above 35 mg per day. Flushing has been seen at doses as low as 30 mg per day. Liver damage however occurs at around 3000 mg/day. Other forms of B3 including nicotinamide may not produce flushing.
  • B5: Most supplements come in 250-500 mg per day which is sufficient.
  • B12: Most products contain cyanocobalamin which is artificial. B-12 in this form may have poor absorption. In those with kidney failure, long-term supplementation of cyanocobalamin can lead to accumulation of cyanide. There has been a shift to preferring methycobalamin which occurs naturally. Currently, the ideal treatment for deficiency is a combination of methycobalamin and adenosylcobalamin, the two active forms [13][14]. However as adenosylcobalamin is not widely available methycobalamin may be suitable. NB: Even though cyanocobalamin may not be optimal it can still be effective

The Bottom Line

B-Complex vitamins are crucial for our energy, mood and vitality.

B-Vitamins can be useful for stress as high levels of stress can depleting.

Deficiency is generally rare however supplementation can be effective.

In general, if a supplement gives you coloured urine it is less effective or is excessively dosed in either B2 or B12. An effective B-vitamin should not affect urine colour.


Nootritious only sources information from select peer-reviewed studies, medical associations and research institutions. It is our strict adherence to this policy that allows us to delivers accurate and actionable advice.