A Message From Dr. Will Cole
The ADA Recommends This Simple Check for Everyone on Metformin. Almost Nobody Gets It.
It costs about as much as a tank of gas, takes one vial of blood, and answers a question one in five long-term metformin users need answered.
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I want to tell you about a recommendation that sits in plain sight, in one of the most widely used clinical documents in American medicine, and almost never makes it into an exam room conversation.
Every year, the American Diabetes Association publishes its Standards of Care.
It is the playbook. If you have type 2 diabetes, your doctor's decisions are shaped by this document, whether you have ever heard of it or not.
Inside it, in the section on medications, is a sentence patients almost never hear about.
The ADA advises that long-term metformin use is associated with vitamin B12 deficiency, and that periodic measurement of B12 levels should be considered in people on metformin, especially anyone with anemia or nerve symptoms like tingling and numbness.[1]
“A simple B12 blood test. That is the whole recommendation.”
And in my experience, when I ask new patients on metformin whether anyone has ever checked their B12, the answer is almost always no.
Why This One Test Matters So Much
Metformin is a good medication. Let me say that without qualification: it has decades of evidence behind it, it is affordable, and it has protected millions of people from the consequences of uncontrolled blood sugar.
Nothing in this article suggests otherwise.
But metformin also interferes with how your gut absorbs vitamin B12, and the evidence for this is about as strong as evidence gets.
It comes from the Diabetes Prevention Program Outcomes Study, a randomized trial follow-up that tracked people for more than a decade:
At five years, 19.1% of metformin users had low or borderline-low B12, compared with 9.5% on placebo. Double.
At thirteen years, it was 20.3%. One in five.
Each additional year of metformin use raised the odds of B12 deficiency by 13%.[2]
Now consider what B12 actually does.
Your nerves rely on it to maintain their protective coating. Your red blood cells rely on it to carry oxygen. Your brain relies on it for clear thinking.
When B12 runs low slowly, over years, it does not announce itself. It shows up as tiredness that gets filed under age. Tingling feet that get filed under diabetes. Foggy thinking that gets filed under getting older.
That last part is the trap.
The symptoms of low B12 look exactly like the things people already expect to feel in their 60s and 70s. Which is why the test matters: without it, there is nothing to catch the drain until it is deep.
If the Playbook Recommends It, Why Does Almost Nobody Get It?
This is the question I find patients get stuck on, and it deserves an honest answer rather than a dramatic one.
Your doctor has perhaps eleven minutes with you. In those minutes, the priorities are the numbers that page them at night: your A1c, your blood pressure, your kidney function. The B12 recommendation says measurement should be considered.
“Considered is a word that loses every fight against an eleven-minute clock.”
Your pharmacist fills the prescription accurately and moves on. The lab runs the panel it was sent. The system works exactly as designed.
It is simply that watching the nutrient cost of a good medication is not written into anyone's job description.
Not a conspiracy. A gap.
I have built a fair amount of my career in that gap, and here is what I tell my own patients on metformin.
The Simplest Next Step
If you take metformin, or a daily heartburn pill, a statin, or a water pill, each of which has its own documented nutrient cost[4], take sixty seconds and run your cabinet through our free Medicine Cabinet Check. You will see immediately which nutrients your medications may be draining, no email required, and you can print the Doctor Visit Cheat Sheet to bring to your next appointment. Whether you ever buy anything from us or not, that is a productive ten minutes.
And if you would rather begin supporting your levels today, The Medicine Cabinet Refill is the routine I designed for exactly this situation: methylated B vitamins in the morning, peptide-bound magnesium at night, with a 90-Night Guarantee judged by your own baseline scorecard, not by our marketing.
Your metformin is doing its job. This is the part that was always yours.
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About the Author
Dr. Will Cole, MD
Functional Medicine Practitioner
Dr. Will Cole is a leading functional medicine practitioner who works to find the root cause of fatigue, inflammation, and hormone imbalance. After reviewing thousands of genetic profiles in his clinic, he formulated MitoMultiply for Longevity Rx to give the body the methylated nutrients it can actually use.
Frequently Asked Questions
Why isn't B12 checked at a normal physical?+
The standard panel is built to catch disease markers your doctor is watching for at night, like your A1c, blood pressure, and kidney function. B12 is not part of that default panel. The American Diabetes Association's own Standards of Care say measurement should be considered for people on long-term metformin, but "considered" is easy to lose inside an eleven-minute visit unless someone asks for it directly.[1]
How common is B12 deficiency in people on metformin?+
In the Diabetes Prevention Program Outcomes Study, 19.1% of long-term metformin users had low or borderline-low B12 at five years, compared with 9.5% on placebo. By year thirteen, it was 20.3%, roughly one in five. Each additional year of use raised the odds of deficiency by 13%.[2]
What does low B12 actually feel like?+
It tends to show up slowly, which is part of the problem. Tiredness that gets filed under age. Tingling feet that get filed under diabetes. Foggy thinking that gets filed under getting older. These symptoms look exactly like what people already expect to feel in their 60s and 70s, which is why a test matters more than a guess.
Should I stop taking metformin?+
No. Metformin has decades of evidence behind it and has helped protect many people from the consequences of uncontrolled blood sugar. Nothing here suggests stopping or changing it. The point of this page is the nutrient it can quietly use up over time, not the medication's value. Never stop or change a prescription medication without consulting your healthcare provider.
What should I actually say to my doctor?+
Something as direct as: "I've been on metformin for years. Could we check my B12?" This is already inside the ADA's own published Standards of Care, so it is not an unusual request. Bringing a printed summary with citations can help keep the conversation short and specific.
Why does the form of B12 matter?+
Most drugstore B12 is cyanocobalamin, a form your body has to convert before it can use it, and that conversion slows with age. Methylated B12 arrives already in the active form, which is why it's used instead of cyanocobalamin in formulations built for this stage of life.[3]
What if my B12 test comes back normal?+
That's a genuinely good outcome, and the honest majority result: about four out of five long-term metformin users are not in the low range. A normal result means one less thing to wonder about. The point of testing is finding out which group you're in rather than guessing.
References
[1] American Diabetes Association. Standards of Care in Diabetes. Section 9, Pharmacologic Approaches to Glycemic Treatment (metformin and vitamin B12 monitoring).
[2] Aroda VR, Edelstein SL, Goldberg RB, et al. Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab. 2016;101(4):1754-1761.
[3] National Institutes of Health, Office of Dietary Supplements. Vitamin B12 Fact Sheet for Health Professionals. ods.od.nih.gov.
[4] Cleveland Clinic. Sarcopenia (Age-Related Muscle Loss), on long-term proton pump inhibitor use, B12 and magnesium malabsorption. my.clevelandclinic.org/health/diseases/23167-sarcopenia.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Never stop or change a prescription medication without consulting your healthcare provider.