What the 2026 diabetes standards say, and what did not change
In January 2026, the American Diabetes Association published its latest Standards of Care. Recommendation 3.10 says clinicians should consider periodic assessment of vitamin B12 in people receiving long-term metformin therapy, especially when anaemia or peripheral neuropathy is present. It carries an evidence grade of B. The wording is deliberately “consider periodic assessment,” not an instruction to test every person immediately after the first prescription [1].
The accompanying discussion gives more context: attention increases with longer exposure, additional B12-deficiency risks, or symptoms that make deficiency plausible. The standards describe annual monitoring after more than 4 years of metformin use or when another B12 risk factor is present, but that is context for higher-risk people, not one schedule that begins with the first tablet and applies to everyone. A clinician connects timing to treatment duration, symptoms, previous results, dietary pattern, gastric or small-bowel surgery, and other medicines that can affect absorption [1, 2].
What did not change is equally important. The recommendation does not tell people to stop metformin, does not say every episode of numbness is caused by low B12, and does not recommend routine injections “just in case.” Metformin remains useful in appropriate diabetes plans, and confirmed deficiency can usually be treated while its cause and the diabetes plan are reviewed. Do not start, stop or change a medicine or supplement on your own [1, 2, 4].
Does metformin really lower vitamin B12?
The short answer is yes: long-term metformin use is associated with a greater likelihood of low vitamin B12, but not everyone who takes it becomes deficient. A randomised trial lasting more than 4 years found a larger fall in B12 and more deficiency in the metformin group than in the placebo group. Long-term follow-up from the Diabetes Prevention Program likewise found low B12 more often with metformin, with risk increasing across years of use [7, 8].
The exact mechanism is not fully settled, but reduced gastrointestinal absorption in some users is the leading explanation. The UK medicines regulator classifies reduced B12 as a common metformin adverse effect and notes that risk rises with longer treatment, a higher daily amount, and pre-existing deficiency risks. That is why monitoring is directed by risk rather than ordered randomly on the same date for everyone [4, 6].
A group-level association cannot diagnose an individual. Fatigue or numbness has many possible causes, and a low or borderline B12 result must be read alongside symptoms and other findings. Conversely, the absence of a striking complaint does not exclude deficiency in a higher-risk person. A comprehensive diabetes review therefore considers medicines, symptoms, diet and previous surgery rather than looking only at HbA1c [1, 3, 5].
Who should discuss B12 testing, and when?
There is no single schedule for every metformin user. The discussion becomes more important with long exposure; numbness, burning or reduced sensation; anaemia or enlarged red cells on a blood count; or otherwise unexplained fatigue. The ADA recommendation gives particular priority to anaemia and peripheral neuropathy and also discusses chronic kidney disease among contexts that increase suspicion [1].
Other risks can combine with metformin: a vegan pattern without a reliable B12 source, previous gastric or small-bowel surgery, a gastrointestinal condition affecting absorption, some acid-suppressing medicines, or older age. One factor does not prove deficiency, but several together may lead the clinician to test sooner or follow more closely. The UK regulator advises testing when suggestive symptoms occur and considering periodic monitoring in people with risk factors [4, 5, 6].
If metformin was started recently and there are no symptoms, additional risks or concerning earlier results, that does not automatically mean a test is needed every few months. After years of use, however, feeling well alone is not a complete screen. Bring the medicine name, duration of use, a full medicine and supplement list, previous surgery and dietary pattern to the appointment. A sound decision comes from that context, not a fixed online timetable [1, 4, 5].
Symptoms are nonspecific, and a normal blood count is not enough
B12 deficiency can present with fatigue, weakness, pallor, breathlessness on exertion, a red or sore tongue, numbness or pins and needles, reduced sensation, balance or gait change, and difficulty with concentration or memory. Every one of these features has other possible causes. Fatigue, for example, can relate to sleep, thyroid disease, iron status, glucose, kidney disease or medicines. Symptoms guide assessment but cannot make the diagnosis by themselves [5, 6, 11].
An important point is that neurological B12 deficiency can occur without anaemia or obvious enlargement of red cells. NICE explicitly says not to exclude deficiency solely because anaemia or macrocytosis is absent. A complete blood count is useful, but it does not close the question when there is new numbness, altered walking or balance, or strong risk factors. Understanding anaemia and the complete blood count helps explain what CBC measures, while the B12 decision needs its own context [5, 10, 12].
Seek prompt assessment if numbness or weakness is progressing, balance or gait changes, new confusion appears, or vision is affected. Sudden one-sided weakness, facial droop, speech disturbance, chest pain, fainting or severe breathlessness is an emergency and should not wait for a vitamin test. NICE also warns that treatment should not be delayed when megaloblastic anaemia is suspected together with significant neurological symptoms [5, 11].
Numbness: diabetic neuropathy or B12 deficiency?
The word “numbness” alone cannot separate the causes. Diabetic peripheral neuropathy often develops gradually in both feet and can cause burning, pain or loss of sensation. B12 deficiency can produce overlapping symptoms and may also cause unsteadiness or impaired awareness of limb position. Both conditions can coexist, particularly in someone with long-standing diabetes and long-term metformin exposure [3, 7].
The 2026 ADA standards stress that diabetic neuropathy is a diagnosis of exclusion and specifically list B12 deficiency in chronic metformin users among alternative, potentially treatable causes. Assessment considers symptom onset and distribution, sensation, reflexes, balance and foot examination, glucose history, medicines, and selected laboratory tests. Nerve-conduction studies or spinal imaging are not routine for everyone, although atypical, rapid, asymmetric symptoms or motor weakness may require broader investigation [3].
Do not assume numbness is “just diabetes,” and do not assume a B12 tablet will resolve any form of numbness. Delaying assessment of reduced sensation can increase the chance that a foot injury goes unnoticed, while treating an unconfirmed cause can delay the correct diagnosis. Check the feet daily if sensation is reduced and seek timely care for a wound, colour change, warmth or swelling while the neurological cause is assessed [3, 5].
How is a borderline result interpreted?
A clinician may begin with total serum B12 or active B12, depending on context and availability. The result must be interpreted using the reporting laboratory’s reference information together with symptoms and risk factors, not a random internet table. NICE advises taking diagnostic blood samples before replacement begins when it is safe to do so, because tablets or injections started beforehand can raise the measured level and make the underlying cause harder to interpret [5].
When a result is borderline and symptoms or risks remain, the clinician may select methylmalonic acid (MMA), or in particular contexts homocysteine. These are not a mandatory panel for every person. Kidney function, folate status, pregnancy and local availability can affect selection and interpretation. NICE evidence reviews and the US National Institutes of Health explain that no single test is perfect in every setting, so the clinical story and the result need to be considered together [5, 6, 12].
A blood count may identify anaemia or altered red-cell size, yet a normal count does not exclude neurological deficiency. Conversely, a low B12 result prompts another question: is metformin the only contributor, or are diet, surgery, malabsorption or an autoimmune cause involved? Our guide to vitamin B12 in plant-based eating explains dietary sources; this update stays focused on the medicine and clinical assessment rather than repeating that food plan [5, 6, 10].
If deficiency is confirmed: tablets, injections, and metformin
Do not stop metformin on your own because a result is low. The UK medicines regulator advises continuing metformin while B12 deficiency is corrected when the medicine is tolerated and there is no separate medical reason to stop it. Decisions about diabetes treatment remain with the prescribing clinician. The aim is to correct deficiency and review its cause without losing the medicine’s benefit or leaving glucose care without a plan [2, 4].
The choice between oral replacement and injections depends on severity, important neurological or haematological features, the suspected cause, and the ability to absorb B12. NICE distinguishes dietary deficiency from deficiency related to malabsorption, surgery or autoimmune disease and links the route of replacement to context and response. An international expert consensus likewise concludes that symptom severity, cause and treatment goals guide route and duration; injections are not automatically better for everyone [5, 10].
Follow-up after treatment asks whether symptoms improved, whether anything new appeared, whether the cause remains, and whether the plan fits the rest of the medicine list. Do not take preventive injections or a multi-ingredient vitamin product without assessment, because this can complicate test interpretation and distract from another cause. The principle that supplements should be targeted to a reason helps keep B12 replacement tied to a diagnosis, goal and review point [5, 9, 10].
What this means for you
If you take metformin, write down when it started, any interruptions, and every medicine and supplement you use. Record new fatigue, a sore or red tongue, numbness, burning, reduced sensation, unsteadiness or changes in concentration. Bring previous blood counts and B12 results instead of repeating tests without a defined question. Ask two direct questions: do my risks make testing appropriate now, and would a borderline result need confirmation or follow-up? [1, 4, 5].
Do not start B12, stop metformin or alter diabetes treatment on your own before the picture is clear. Progressive neurological symptoms or possible severe anaemia deserve prompt assessment rather than waiting for a routine review. Sudden one-sided weakness, speech disturbance, fainting or severe breathlessness requires immediate emergency care because these signs need urgent evaluation for causes more serious than a possible vitamin deficiency [3, 5, 11].
Diabetes and internal-medicine assessment is available at the Maadi branch only. Nutrition follow-up can be arranged in Maadi or Fifth Settlement, or through the online nutrition service when suitable. Youssef Hagag is a physician and medical researcher who contributes content, but he is not a bookable clinic doctor. If you need to connect symptoms with medicines, laboratory findings and the diabetes plan, Book an assessment with the medical team at La Rose and bring the medicine list and previous results [1, 2].
