Taking vitamin B12 supplements but still seeing low levels on blood tests? The issue may not always be how much B12 you consume. In some cases, the body may have trouble absorbing the vitamin.
Vitamin B12 from food follows a complex absorption process. Stomach acid helps release B12 from food proteins, after which it binds with a substance called intrinsic factor before being absorbed in the small intestine. Conditions affecting this process can lead to deficiency even when dietary intake is adequate.
What Can Stop B12 Absorption?
Several health conditions can interfere with B12 absorption, including atrophic gastritis, pernicious anaemia, coeliac disease and Crohn’s disease. Certain stomach or intestinal surgeries can also affect absorption.
Long-term use of some medicines may also play a role. Metformin and acid-reducing medicines such as proton-pump inhibitors can affect B12 levels over time. This does not mean people should stop prescribed medicines, but persistent deficiency should be discussed with a doctor.
Is a Higher-Dose Supplement Always Better?
Not necessarily. B12 supplements are already in a form that does not require the vitamin to be released from food proteins, but the main absorption pathway still depends on intrinsic factor. High oral doses can allow a small amount of B12 to be absorbed passively.
There is also no strong evidence that methylcobalamin is automatically absorbed better than cyanocobalamin.
When Should You Get Checked?
Persistent low B12 deserves investigation rather than simply increasing supplement doses. Doctors may consider additional testing, including methylmalonic acid (MMA) when blood B12 results are borderline. Symptoms such as numbness, tingling, balance problems, weakness or cognitive changes can also occur with B12 deficiency.
The Bottom Line
If B12 levels remain low despite supplementation, the underlying cause may be poor absorption, a medical condition or medication-related changes. Finding the reason can be more important than simply taking a higher dose.