What Can Contribute to Low Vitamin B12?

Low vitamin B12 is a common nutrient deficiency that can have several contributing causes.

According to Healthdirect and the Royal College of Pathologists of Australasia (RCPA), vitamin B12 may be low for several reasons, including:

• Inadequate intake of vitamin B12-containing foods,
• Poor absorption and pernicious anaemia,
• Digestive conditions or surgery that affect nutrient absorption,
• Older age, and
• Some medicines that may interfere with nutrient absorption.

Symptoms linked to low B12 are non-specific and can have many other causes. For a doctor or healthcare provider, working out why your B12 is low usually involves looking at your history, diet and medicines alongside blood test results.

This article will help you understand:

• Risk factors for low B12,
• Signs and symptoms associated with low B12,
• How B12 status is checked,
• How to manage low B12,
• Australian B12 intake guidelines, and
• When it’s worth speaking to your doctor about low B12.

What is vitamin B12 and why does it matter?

According to Eat For Health, vitamin B12 is a nutrient the body needs to produce normal, healthy blood, for making DNA and for keeping the nervous system working properly.

The symptoms of low B12 are general and non-specific and can often have other causes, which is why doctors and healthcare providers assess B12 status by taking your medical history and through blood testing.

How does the body absorb vitamin B12?

Vitamin B12 is bound within food and released during digestion. There, it binds to a substance called intrinsic factor, and is absorbed in the last section of the small intestine, known as the terminal ileum.

If any part of that pathway is disrupted, less B12 reaches the bloodstream. This is why low B12 can occur even if someone's diet contains adequate amounts.

Common causes of low vitamin B12

Australian consumer-health guidance from Healthdirect and clinical guidance from the RCPA identify several risk factors for low B12:

• Inadequate intake of vitamin B12-containing foods,
• Poor absorption and pernicious anaemia,
• Digestive conditions or surgery that affect nutrient absorption,
• Older age, and
• Some medicines that may interfere with nutrient absorption.

Inadequate dietary intake

Vitamin B12 is found mainly in animal foods, so diets that contain little to no meat, eggs and dairy can contribute to low B12 over time. The RCPA identifies strict vegan diets as a primary cause of vitamin B12 deficiency, and Dietitians Australia adds that fortified foods can be an important source of the nutrient for people following vegetarian or vegan diets.

It’s important to remember that eating enough B12 does not rule out absorption problems or other factors that might contribute to deficiency.

Poor absorption and pernicious anaemia

If there are absorption problems, B12 can be low even when a person's diet contains adequate amounts. There are some digestive conditions, like hypochlorhydria and pernicious anaemia, that can interfere with the body's ability to absorb B12. Both Healthdirect and the RCPA list poor absorption as a major cause of deficiency.

Doctors and healthcare providers assess low B12 blood test results together with symptoms and medical history when considering the likely cause of the deficiency and how to manage it.

Digestive conditions and surgery

Conditions that affect the digestive system, particularly a section of the small intestine called the ileum, can reduce how much B12 the body absorbs. Healthdirect and the RCPA list several of these conditions, including:

• Ileum-related malabsorption diseases (including Crohn's disease),
• Gastric bypass surgery, and
• Bariatric surgery.

If you have low B12, it’s important to tell your doctor or healthcare provider about any history of digestive disease or surgery that could be interfering with B12 absorption.

Older age

Healthdirect identifies older age as a risk factor for low vitamin B12. Decline in gastric function and production of digestive acids and enzymes required for vitamin B12 absorption is common as we age.

Some medicines

Some medicines can interfere with the absorption of vitamin B12. If you take a prescribed medicine and have low B12, do not stop or change taking your prescription without seeing your prescribing doctor or healthcare provider.

What signs can be associated with low vitamin B12?

Healthdirect lists low vitamin B12 signs to include:

• Tiredness,
• Weakness, and
• Neurological symptoms, like tingling or numbness.

None of these signs are specific to low B12, and many other causes can produce the same symptoms.

If symptoms like these are persistent or concerning, speak with a doctor or healthcare professional, who can decide whether B12 testing is needed.

How is low vitamin B12 checked?

Vitamin B12 status is assessed with a blood test.

Blood test results are only part of the overall picture, and need to be interpreted by a doctor or healthcare provider alongside symptoms, diet, medical history, any previous surgery and current medicines. According to the RCPA, vitamin B12 reference ranges vary between laboratories, so they need to be interpreted within the reference ranges used by the laboratory that ran the test.

Which foods contain vitamin B12?

Dietitians Australia lists animal-based foods as the primary sources of vitamin B12, including:

• Red meat,
• Poultry,
• Seafood,
• Milk,
• Cheese, and
• Eggs.

For people who eat few or none of these foods, fortified foods can be an important source of vitamin B12. Commonly fortified foods include:

• Breakfast cereals,
• Plant-based milks and dairy alternatives,
• Plant-based meat alternatives,
• Nutritional yeast, and
• Tofu and soy-based products.

To be sure these foods are fortified with vitamin B12, you will need to carefully check the label.

How much vitamin B12 do adults need?

The Australian and New Zealand Recommended Dietary Intakes (RDIs) for vitamin B12 for adults, published by Eat For Health (NHMRC) are:

• Adults (19 years and over): 2.4 µg per day
• Pregnancy: 2.6 µg per day
• Lactation (breastfeeding): 2.8 µg per day

These are reference values for recommended daily dietary intake for healthy people at each life stage, not treatment doses for correcting a vitamin B12 deficiency.

How can I support adequate vitamin B12 intake?

Regularly including B12-containing foods, whether animal-derived or fortified, is the most practical way to support adequate dietary intake.

However, intake is only one part of vitamin B12 status and other factors like absorption problems, medicines and other factors may need to be discussed with your doctor or healthcare provider.

When should you speak with a doctor?

Speak with your doctor or healthcare provider if you have persistent and/or concerning tiredness, weakness, tingling, or numbness.

It is also important to speak to your doctor or healthcare provider about vitamin B12 if you’re a vegan or vegetarian or you have a digestive condition that affects absorption, have had previous stomach or bowel surgery, you’re of older age, or you’re taking prescribed medicines.

If a test has confirmed that you have low B12, the doctor or healthcare provider who ordered the test will explain what the results mean for you.

FAQ's

Can a poor diet cause low vitamin B12?

Yes. A diet that contains little or no vitamin B12 can contribute to low B12 over time.

Because animal-based foods are the primary sources of dietary vitamin B12, fortified foods can be an important source of the nutrient for vegetarians, vegans and people with low animal food intake.

Diet is only one possible cause of low B12, and absorption problems or other factors can play a role even when dietary intake is adequate.

Who is more likely to have low vitamin B12?

Risk factors for low vitamin B12 include:

• Low dietary intake (especially for vegetarians, vegans and people who eat little to no animal-based foods),
• Digestive conditions affecting nutrient absorption (including pernicious anaemia),
• Older age, and
• Some prescribed medicines that may interfere with vitamin B12 absorption.

If you have one or more of these risk factors, it doesn’t necessarily mean you have low vitamin B12. Your doctor or healthcare provider will consider these risk factors alongside your symptoms and diagnostic testing to confirm your B12 status.

Can low vitamin B12 cause tingling or numbness?

Yes. Tingling and numbness are among the neurological symptoms associated with vitamin B12 deficiency. Tingling and numbness can also have other causes. Your doctor or healthcare provider will assess all possible causes of these symptoms, including assessing your vitamin B12 status.

How is low vitamin B12 checked?

Low vitamin B12 is checked with a blood test. Your results will need to be interpreted by your doctor or healthcare provider alongside symptoms, diet, medical history, and prescribed medicines.

Do adults need vitamin B12 each day?

Yes.

The Australian recommended dietary intake (RDI) for vitamin B12 is 2.4 µg a day for adults aged 19 and over, rising to 2.6 µg a day during pregnancy and 2.8 µg a day during breastfeeding.

When should I see a doctor about low vitamin B12?

You should see your doctor or healthcare provider if you have persistent or concerning symptoms, especially if you have a recognised risk factor for low B12. They can decide whether testing is appropriate for you and interpret your results.

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