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The Low Down on Metformin and Vitamin B12 Deficiency

So many women with PCOS are prescribed Metformin (an insulin-sensitizing drug) to manage their Polycystic Ovarian Syndrome. And for good reason too. Metformin has been shown to improve many aspects of PCOS, including weight loss, fertility and improved testosterone levels (1). But, it also leads to Vitamin B12 deficiency if used at high doses or for long periods of time. So, here’s what you need to know about Metformin and Vitamin B12 deficiency with PCOS.

What is Metformin?

Metformin-and-Vit-B-deficiency-doctorAs I have already mentioned, Metformin is an insulin sensitizing drug that is often prescribed for women withPCOS. It works by decreasing absorption of glucose through the intestines, lowering the amount of glucose produced by the liver and making the body more sensitive to the insulin that is being produced.

The overall effect of Metformin use for PCOS is lowered testosterone levels, improved ovulation and fertility as well as a more regular menstrual cycle.

This is all sounding good, right? Well, it is good although there are some nasty side effects. A full discussion on Metformin is not going to be dealt with now, though. I really want to hone in on Metformin’s effect of Vitamin B12 levels as this could be affecting you right now.


Vitamin B12

Vitamin B12 is a vitamin that is vital for the body’s functioning. It is important for red blood cell formation, neurological function and DNA formation. If you are deficient in this important vitamin, it could lead to anaemia and neurological problems. (including memory loss – something that I have seen cropping up more often in PCOS communities). (2)


Metformin and Vitamin B12

Right, so this is where it gets interesting. Recent studies have shown that Metformin decreases Vitamin B12 levels, particularly when used long-term and when taken at high doses. Women with PCOS do tend to take Metformin at high doses for a long period of time and are therefore at risk of Vitamin B12 deficiency.

So, if you are taking Metformin, you may be tempted to start taking a Vitamin B12 supplement. Not so fast, though. Metformin lowers Vitamin B12 absorbency because it alters a Calcium-based reaction that allows the body to absorb the vitamin.

So, Calcium supplementation is what you are after, not Vitamin B12 (3).


Metformin-and-Vit-B-deficiency-calciumOkay, so now we know we need more Calcium to counteract the Vitamin B12 deficiency caused by Metformin. Before you rush off to stock up on milk and cheese, remember that Dairy is a no-no for women with PCOS. So, where does that leave us? Well, you can get calcium from other dietary sources, or you can take a calcium supplement.

Dietary sources of Calcium

There are so many sources of calcium, apart from dairy. Here is a great table from the National Osteoporosis Foundation.

The thing is though, research suggests you should be taking about 1200mg per day of Calcium to combat the Vitamin B12 deficiency (4). It is going to be difficult to source that amount of Calcium from your diet alone. So, I would recommend taking a Calcium supplement.

Calcium Supplementation

This seems to be quite a controversial subject at the moment but the research does suggest supplementation. So, with that in mind, I would recommend taking a slow release Calcium Citrate as calcium citrate seems to have less side effects than calcium carbonate.

Apart from this Vitamin B12 Deficiency, there are other reasons you may want to reconsider taking Metformin for PCOS.

Summing it Up

So, to sum it up, if you are taking high doses of Metformin to manage your PCOS or have been taking it for a long time, you may be at risk of Vitamin B12 deficiency. You can combat this by taking a Calcium supplement to increase Vitamin B12 absorption. However, before you do start taking any supplements, please speak with your doctor first!

Are you taking Metformin? I’d love to hear your thoughts and experiences with it in general! Leave me a comment below!

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Tarryn Poulton

Tarryn Poulton

Tarryn Poulton is a PN1 Certified Nutrition Coach and PCOS expert who has been a leader in the online PCOS space for over 8 years. Tarryn has the support of leading clinicians from around the world who support her scientific approach to understanding and talking about PCOS this includes all medical journals and ongoing research. You can read more about Tarryn and the team here.

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