Vitamin B12 and your medicines: the metformin and heartburn-pill link most people miss
Two of the most-taken drug groups quietly lower vitamin B12. Metformin (the first-line type-2 diabetes drug) reduces B12 absorption in a dose- and duration-dependent way — its FDA label flags it and advises periodic B12 checks. Proton pump inhibitors (omeprazole, esomeprazole, pantoprazole) and H2 blockers cut the stomach acid that frees B12 from food, so years of use can pull levels down too. Low B12 shows up as fatigue, tingling, and anaemia — often blamed on everything but the pill. Every number below is one ordinary serving, from USDA FoodData Central.
The part people get wrong
This is not a reason to stop metformin or your reflux drug — both are doing important jobs, and the fix is monitoring, not avoidance. If you have taken either for years, ask your prescriber to check a B12 level (the metformin label itself recommends it), especially if you feel unusually tired or have numbness or tingling in the hands or feet. B12 from food or a supplement corrects a deficiency; you do not have to choose between the medicine and your B12.
Vitamin B12 in common foods — per serving, not per 100 g
Values from USDA FoodData Central for the serving shown. These are foods people actually eat: ranking the whole USDA database by density would put dried thyme and defatted soy flour at the top, which is accurate and no use to anyone.
| Food | Serving | Vitamin B12 (µg) |
|---|---|---|
| Clamscooked, moist heat | 3 oz (85 g) | 84 |
| Beef livercooked, pan-fried | 3 oz (85 g) | 70 |
| Fortified cereal100% DV per serving | 1 serving (30 g) | 6 |
| SalmonAtlantic, cooked | 3 oz (85 g) | 4.8 |
| Tunalight, canned in water | 3 oz (85 g) | 2.5 |
| Beefground, cooked | 3 oz (85 g) | 2.4 |
| Milkwhole, 3.25% milkfat | 1 cup (244 g) | 1.3 |
| Yogurtplain, low fat | 1 container (8 oz) (227 g) | 1.1 |
| Eggwhole, cooked | 1 large (50 g) | 0.6 |
| Cheesecheddar | 1 slice (1 oz) (28 g) | 0.5 |
| Chickenbreast, roasted | 3 oz (85 g) | 0.3 |
The medicines this affects
Drugs in our catalog from the classes involved — biguanide and proton pump inhibitor. Each page carries that drug’s own FDA label.
Frequently asked questions
Which foods are highest in vitamin b12?
Per serving, the highest on this list is clams — 84 µg in 3 oz (85 g), per USDA FoodData Central. These are common foods rather than the absolute maximum in the USDA database: ranking every food by vitamin b12 density puts dried herbs and defatted soy flour at the top, which is true and useless to someone deciding what to have for dinner.
Do I need to avoid vitamin b12 if I take these medicines?
This is not a reason to stop metformin or your reflux drug — both are doing important jobs, and the fix is monitoring, not avoidance. If you have taken either for years, ask your prescriber to check a B12 level (the metformin label itself recommends it), especially if you feel unusually tired or have numbness or tingling in the hands or feet. B12 from food or a supplement corrects a deficiency; you do not have to choose between the medicine and your B12.
Where do these numbers come from?
USDA FoodData Central (SR Legacy), for the household serving shown next to each food — not per 100 g. Per-100-g figures are what most "foods high in vitamin b12" lists use, and they are misleading: nobody eats 100 g of dried thyme.
Sources
- Vitamin B12 — NIH Office of Dietary Supplements, Health Professional Fact Sheet ↗
- Metformin Hydrochloride tablet — FDA label, Vitamin B12 (DailyMed) ↗
- USDA FoodData Central, SR Legacy ↗
Nutrient values are USDA reference data for the serving shown and vary with variety, growing conditions and cooking. This page is general information, not medical advice — never change your diet or your dose on the strength of a web page. Talk to whoever manages your treatment.