Vitamin B12 deficiency: symptoms, causes and when to test

Which complaints can point to a vitamin B12 deficiency?

Vitamin B12 is needed for the production of red blood cells and for the maintenance of the nervous system. When the stores run low, most people notice it first in their energy:

• persistent fatigue
• becoming short of breath more quickly during exertion
• paleness
• the feeling that their concentration is not what it used to be
• irritability, a low mood or forgetfulness

Each of these complaints can have dozens of other causes, which is exactly what makes it so difficult to judge on your own.

In addition, there are complaints that point more specifically towards the nerves:

• tingling or numbness in fingers and toes
• a burning sensation on the tongue
• an unsteady balance
• loss of strength

These neurological complaints are important to take seriously, because with a long-standing deficiency they recover less well than the complaints linked to the blood count. If you recognise this, discuss it with your GP, even if you intend to arrange a blood test yourself.

Causes: taking in too little or absorbing too little

The first route is diet. Vitamin B12 comes almost exclusively from animal products: meat, fish, eggs and dairy. Anyone eating a vegan diet structurally takes in too little without a supplement or fortified products. With a vegetarian diet it depends strongly on how much dairy and egg is on the table each day.

Because the body builds up a reserve in the liver, it can take years before a deficiency becomes visible. That is precisely what makes it deceptive: the complaints arrive late, and then often gradually.

The second route is absorption, and that one is more often overlooked. Absorbing B12 from food requires stomach acid, plus a substance produced by the stomach lining. Various situations can reduce that absorption:

• long-term use of acid-reducing medication
• metformin, the most commonly prescribed medicine for type 2 diabetes, where a lowered B12 value is a known and well-documented effect with longer-term use
• gastric surgery
• bowel conditions such as coeliac disease and Crohn's disease
• the natural decline in stomach acid at an older age

In all these cases you can eat plenty of B12 and still build up a deficiency.

Why test, and when?

A measurement is especially worthwhile if you belong to a risk group or if you have complaints that simply do not pass. Concretely:

• with a plant-based diet
• with long-term use of acid-reducing medication or metformin
• after gastric surgery
• with a bowel condition
• with persistent fatigue or tingling without a clear explanation

In those situations a measurement replaces guesswork with a value a doctor can interpret.

If you already take a B12 supplement, timing matters. Supplementation raises the measured value, so a result shortly after starting says little about your baseline.

If you want to know whether you would have a deficiency without a supplement, ideally have the test done before you start, or discuss with a doctor how to read the result in your situation. If you instead want to check whether supplementation is working, testing after a few months is more logical.

How do you read the result?

The laboratory states the reference values that apply there alongside your result, and those are leading. A value below the lower limit fits a deficiency, but a result just inside the range does not fully rule one out: part of the measured B12 is not available to the cells.

That is why B12 is often not viewed in isolation in practice, but placed alongside the blood count and folate, and supplemented with a follow-up test where needed. Your complaints and your diet and medication pattern belong in that assessment too.

Testing at Bloodworks

At Bloodworks you have vitamin B12 drawn at one of the 1000+ collection points in the Netherlands, without a referral and at a time that suits you.

Every result is reviewed by a doctor and delivered as a personal PDF report, with an explanation of the value and, where applicable, the advice to contact your GP. If you want a broader picture of your vitamin status, you can combine B12 with vitamin D and folic acid, among others, in a single blood draw with the Vitamins, minerals and electrolytes package.