Metformin's negative effect on vitamin B-12

Since starting Rapamycin almost 2-years ago. My physician wanted to monitor my blood every 3-6 months with a full blood work up. Almost 1 year into my use of Rapamycin I was reading how the combination of Rapa with Metformin was a good choice.

This was my B-12 before taking Metformin.

A healthy 933 within the range 271 - 1171.

After taking Metformin for several months I mentioned it to Dr. Yelena Budovskaya anti-aging specialist. She said that my vitamin B-12 would take a hit. Be sure to take B-12 supplements. I had my blood work done after her prediction and she was correct I had taken a significant hit. My B-12 dropped to half in the range.

I have been on B-12 supplements ever since her advice and my Blood work today is at it’s highest in the range.

So I am just passing this along to all of you who are on Metformin with Rapa… watch your B-12 levels.


What type of B12 are taking?
Cyanocobalamin or hydroxocobalamin or?
Oral or injectable?

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You bring up an excellent point Joseph - For the B12, do you know your MTHFR genetic status? If you do not have any deficiencies then you probably can take any form of B12. However, if you cannot absorb B12 due to SNP variant in FUT2 gene, I recommend methylcobalamin form of B12.

I had my genetic status run by Yelena and had no deficiencies. So I used this Walmart B-12 gummies 1000mcg - I take 2 per night. Oral cyanocobalamin . Results were great as you can see.


Careful, you don’t want B12 levels too high either. From ConsumerLab review article:


Wow… that is concerning too! Appreciate sharing this! Looks like I will switch to methylcobalamin form of B12. That way I can take less and still maintain good B-12 levels. Finding the SWEET spot of B-12. Mayo Clinic’s take. Vitamin B-12 - Mayo Clinic