10 May 2023

The top causes of vitamin B deficiency explained

The top causes of vitamin B deficiency explained
Medically reviewed by Dr Anojan Arulananthan, MBBS, BSC

When we talk about vitamin B deficiency, we usually mean vitamin B12 or B9 (folate). But here’s the thing: you can be deficient in any one of the 8 different B vitamins, although some deficiencies are more common than others.

Vitamin B12 deficiency is one of the most common – especially if you’re vegan, vegetarian or pregnant.

So, what causes vitamin B deficiency? And which ones are you most likely to be deficient in?

Read on to find out the top causes of low vitamin B levels, and how to check your levels.

What is vitamin B?

There’s no one singular ‘vitamin B’ – there are 8 (1).

The B vitamins, sometimes called the ‘B complex’, are a group of vitamins that include:

  • B1 (thiamine)
  • B2 (riboflavin )
  • B3 (niacin)
  • B5 (pantothenic acid)
  • B6 (pyridoxine)
  • B7 (biotin)
  • B9 (folate)
  • B12 (cobalamin)

B vitamins play a lot of essential roles in your body, such as making red blood cells and helping your body’s cells use energy.

They’re also water-soluble vitamins. This means they dissolve in water when they enter your body, as opposed to fat-soluble vitamins (which – you guessed it – are dissolved in fat).

Your body can’t store large amounts of water-soluble vitamins for later use, which is why you need to get your vitamin B fix each day. 

Why is vitamin B important?

All the B vitamins help your body convert food into energy, but many have extra functions too.

Here’s a bit more about each vitamin’s role in your body:

  • B1 (thiamine) – helps maintain normal nerve function
  • B2 (riboflavin) – works as an antioxidant, preventing free radicals from damaging cells
  • B3 (niacin) – improves circulation, helps create and repair DNA
  • B5 (pantothenic acid) – promotes healthy skin, hair and eyes, keeps your digestive tract healthy
  • B6 (pyridoxine) – keeps your nervous system healthy and strengthens your immune system
  • B7 (biotin) – helps keep your hair, skin and nails healthy
  • B9 (folate) – helps form red blood cells, maintains brain health
  • B12 (cobalamin) – helps make red blood cells and anaemia prevention

How do you test for vitamin B?

You can test your vitamin B levels with an at-home blood test.

Our vitamin B12 blood test looks at your B12 specifically, while our advanced vitamin blood test incorporates your B9 (folate) and vitamin B12, along with vitamin D.

How common is vitamin B deficiency?

Vitamin B12 and B9 deficiency is more common in pregnant and older people.

For example, around 20% of people over 60 are deficient in B12 (2). For those under 60, this drops to around 6%.

One study showed that just under 50% of pregnant women showed signs of vitamin B12 deficiency (1).

However, if you’re following a vegan diet, these factors are less important, and you should be aware of deficiency risk regardless of age or whether you’re pregnant.

Other vitamin deficiencies, such as vitamin B1 (thiamine), are rare in the UK.

What are the top causes of vitamin B deficiency?

Lack of vitamins in your diet

Not getting enough B vitamins in your foods can lead to deficiency

Excessive alcohol use

Alcohol addiction reduces your body’s ability to absorb vitamins properly

Certain medical conditions

For example, pernicious anaemia is a very common cause of vitamin B12 deficiency

Who is most at risk for vitamin B deficiency?

If you’re elderly or pregnant, you’re more at risk for vitamin B deficiencies.

Also, if you eat a diet that doesn’t include much meat, fish and dairy (such as a vegan diet), you’re at risk of vitamin B12 deficiency. This is because vitamin B12 isn’t found in plant-based foods.

You can reduce your risk of vitamin B deficiency by taking B12 supplements and eating fortified foods, such as cereals and bread.

What are the symptoms of vitamin B deficiency?

Some of the signs and symptoms of folate (B9) and B12 deficiency include:

  • extreme tiredness
  • pins and needles
  • mouth ulcers
  • problems with your vision
  • rapid breathing or shortness of breath
  • headaches
  • muscle weakness
  • indigestion
  • loss of appetite
  • noticeable heartbeats (palpitations)
  • diarrhoea
  • a sore or red tongue
  • problems with your memory and understanding (cognitive changes)

The final word

So there you have it, the top causes of vitamin B deficiency explained, along with some common signs and symptoms of low levels.

If you think you might be deficient in vitamin B12 or folate (B9), then speak to your GP and consider taking our advanced vitamin blood test.


1. Anaemia - B12 and folate deficiency: How common is it?


2. B Vitamins and the Brain: Mechanisms, Dose and Efficacy – A Review


3. Vitamin B12 and folate statuses are associated with diet in pregnant women, but not with anthropometric measurements in term newborns


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