Metformin and Vitamin B12

Written by Dr Jatin Joshi, co-founder and Chief Medical and Scientific Officer of Personally, and a researcher at the University of Oxford's Centre for Evidence-Based Medicine. I have a financial stake in this company, and you should weigh what follows with that in mind.

You take metformin, you have heard something about it and vitamin B12, and you want to know whether this is something to worry about. The short version is calming: there is no need to be alarmed, but there is a simple, sensible thing worth doing, and it is worth understanding why.

First, the reassurance. Metformin is a well-established and effective medicine, whether you take it for type 2 diabetes or for polycystic ovary syndrome. Nothing here is a reason to stop it or to change how you take it. The B12 question is a small thing to manage alongside a medicine that is doing useful work, not a mark against the medicine itself.

Here is the actual link. Long-term use of metformin is linked with lower vitamin B12 levels in some people. It is more likely the longer you have been taking it, and at higher doses, and the reason appears to be that metformin can interfere with the way B12 is absorbed further down in the gut. This is a recognised association, well enough established that it is worth knowing about if you have been on metformin for a good while.

Notice the language, because it matters. Metformin is linked with lower B12 levels. It does not strip B12 out of everyone who takes it, and plenty of people on metformin have entirely normal levels. It is a tendency worth checking, not a certainty to fear.

A few things stack the odds. The longer you have been taking it, measured in years rather than months, the more the association tends to show. Higher doses matter too. And your starting point matters, so if you eat little or no meat, fish, eggs or dairy, or you are older, both of which make low B12 more common anyway, then metformin is one more factor pushing in the same direction. If several of those describe you, it is a stronger reason to have the check done rather than a reason to worry harder.

B12 is one of those quietly important nutrients. Your body uses it for energy, for making healthy red blood cells, and for the normal working of your nerves. If levels drift low over a long period, the first signs are often vague, tiredness, feeling run down, and if it goes further it can eventually show up as nerve-related symptoms such as tingling or numbness in the hands and feet. Those particular symptoms are worth mentioning to your doctor rather than sitting on, partly because they can be mistaken for other things. None of this is likely to be dramatic, and it is very manageable once looked at, which is rather the point of checking.

This is the part that actually matters, and it is simple. If you have been on metformin for a while, ask your doctor to check your B12 with a blood test, and to keep an eye on it periodically rather than as a one-off. That check belongs with them, not with an article and not with a supplement, because they can see your full history, weigh it against any symptoms you have, and interpret the result properly. A single number on a form means less than a doctor reading it in the context of you, which is a good part of why guessing at this from home is a poor substitute for asking.

If a test shows your B12 is genuinely low, correcting it is also their call. A real deficiency sometimes needs more than a general supplement can offer, higher doses or, in some cases, injections, and that is a treatment decision for your doctor. And to say it once more, low B12 is never a reason to stop your metformin. It is a reason to top up the B12, under guidance.

Where does a formula like ours come in. In a supporting role, and honestly stated. A formula that knows you take metformin can include vitamin B12, in the well-absorbed methylcobalamin form, at a sensible everyday level to help maintain a normal picture over time. What that is not is a treatment for a diagnosed deficiency. If a blood test finds a genuine shortfall, that goes back to your doctor and may need more than any general formula provides. The two things sit side by side: your doctor handles testing and any real deficiency, and a sensible daily amount can support the ordinary picture in between.

The thread running through all of this is simply that a supplement should know what medicines you are on. We ask before we formulate. Most of the industry hands you the same blend regardless, which is the actual problem worth solving here.

If you would like to see how that works for your own situation, the quiz is where it starts. It asks what you take, which is the whole idea, and it is a way to understand where nutrition fits around your medicine, not a checkout.