Vitamin B12 Deficiency

Vitamin B12 deficiency is caused by inadequate dietary intake or malabsorption of vitamin B12 (1).

This post will discuss the role of vitamin B12, your daily needs, sources of vitamin B12, and the cause and symptoms of deficiency. 

WHY DO I NEED VITAMIN B12?

Vitamin B12 has many roles in your body. It has the following roles: 

• Is used to make red blood cells
• Helps to release energy from food
• Is used in processing folic acid
• Used within the nervous system to maintain healthy nerve function (2)
• Contributes to the normal function of the immune system and reduction of tiredness and fatigue (2)

WHAT ARE THE VITAMIN B12 REQUIREMENTS? 

Daily needs for adults (aged 19-64) are 1.5 micrograms (3). Your requirements may be higher if you are vegan (4).

For most people, a normal balanced diet will provide them with enough vitamin B12 as it is found mostly in animal products. 

HOW TO MEET THE NEEDS FOR VITAMIN B12 IF YOU ARE VEGAN? 

It is quite difficult to get vitamin B12 from a vegan diet. Many vegans often suffer from a deficiency if they don’t take extra measures to ensure their diet has a regular source.

If you are vegan, you should follow one of the listed recommendations to avoid vitamin B12 deficiency (4):

• Eat 2-3 portions of fortified foods a day to get at least 3 mcg of vitamin B12.
• Take a supplement that provides at least 10 mcg of vitamin B12 every day.
• Take a supplement that provides at least 2000 mcg of vitamin B12 once a week.

The less often you consume vitamin B12, the higher dose you will need to cover your needs. This is because the vitamin is better absorbed when consumed when taken little and often (4). 

SOURCES OF VITAMIN B12

As already mentioned, vitamin B12 is present in animal products. Examples of animal source foods include:

• Dairy (e.g cheese/yogurt/milk)
• Eggs
• Meat
• Fish

You can get vitamin B12 also from a vegan diet as many products are fortified:

• Fortified breakfast cereals
• Fortified vegan spreads
• Fortified soya/almond/coconut milk
• Fortified nutritional yeast

Always check the label to make sure the product is fortified as B12 does not occur naturally in these foods.

HOW IS VITAMIN B12 PROCESSED?

Foods containing vitamin B12 are first broken down in the stomach. This allows vitamin B12 to be released and bound to specific proteins. 

These proteins then carry the B12 out of the stomach and into the small bowel, where they are separated by pancreatic juice (5). 

This time the vitamin is bound to a ‘glycoprotein’ known as an intrinsic factor. This intrinsic factor acts as a key for the B12 which is then absorbed into the blood (5). In the blood, it again binds to another protein and becomes ‘active B12’ (5).

VITAMIN B12 DEFICIENCY

A survey from the USA showed that the prevalence of B12 deficiency is around 3% in the age group 20-39 years old. Prevalence increases with age and in people older than 70 years old, it reaches 6% of the USA population (1).

Symptoms of vitamin B12 deficiency are (6):

• Muscle weakness
• Disturbed vision
• Depression
• Memory problems
• Extreme fatigue
• Mouth ulcers

As mentioned, it is fairly uncommon to have a vitamin B12 deficiency due to lack of dietary intake diet, unless you are vegan.

WHO IS AT RISK OF VITAMIN B12 DEFICIENCY?

Aside from vegans, some medical conditions can lead to vitamin B12 deficiency.

This means that the body may be unable to process vitamin B12 correctly, leading to deficiency regardless of the amount eaten.

The following medical conditions can lead to vitamin B12 deficiency;

1. Surgeries

Surgeries that have removed all or part of the stomach and pancreas will reduce a person’s ability to process vitamin B12 (7).

2. Medications

Certain medications may affect a person’s ability to absorb vitamin B12 e.g diabetes type 2 medication (metformin) and proton pump inhibitors (8, 9).

3. Intestinal conditions

Inflammatory bowel disease like Crohn’s disease and the autoimmune condition coeliac disease will cause damage to the lining of the intestine, reducing its ability to absorb vitamin B12 (10).

4. Helicobacter pylori infection

Helicobacter pylori infection causes gastritis and impacts gastric acid production and availability of intrinsic factor. Intrinsic factor is needed for transport of the vitamin B12 (11).

5. Pernicious anaemia

An autoimmune condition where your immune system is attacking healthy cells, destroying the ability of the intrinsic factor to work effectively (12).

NOTE: Whilst it is important to ensure your diet has good sources of vitamin B12, you must speak to a doctor if you feel you have a deficiency. You may have an underlying condition which needs the appropriate management or require B12 injections.

HOW IS VITAMIN B12 DEFICIENCY TREATED?

Treatment of vitamin B12 deficiency depends on the cause.

If your vitamin B12 deficiency is due to inadequate B12 dietary intake, the deficiency should improve by taking oral or inject supplements dependent on the level of vitamin B12 in your blood. To maintain healthy levels you should consider dietary modification or take supplements to prevent further issues (13).

Whether you have B12 deficiency due to taking certain drugs (e. g. Metformin), oral supplements should improve it (13).

If the cause of deficiency is malabsorption due to Crohn’s disease or Coeliac disease, serum level usually corrects as the bowel heals. But you may need oral or injection supplements depending on the level (13).

If you have pernicious anaemia, you will need an injection as oral supplements won’t make a difference (13).

SUMMARY

Vitamin B12 has a role as a cofactor in many different body functions.

Vitamin B12 needs to be obtained from the diet – it is found in animal source foods and fortified products. If you can’t ensure sufficient intake with diet, you should supplement it to avoid deficiency.

There are some medical conditions that cause deficiency regardless of the intake. If that is the case for you, talk to your doctor.

Written by Barbara Lešnik Student Dietitian 2022, reviewed by Serena Bansal Registered Dietitian BSc Hons, and Kirsten Jackson Consultant Dietitian BSc Hons, RD, PG Cert