Vitamin B12 deficiency builds slowly and quietly, and the early signs, like tiredness, brain fog and tingling feet, are easy to blame on a busy life. If you’re vegetarian, over 35 or on certain common medications, your risk is higher than you might think. Here’s how to spot the problem, test for it and keep your levels where they should be.
Key takeaways
- Adults need 2.4 mcg of vitamin B12 a day, according to the NIH Office of Dietary Supplements.
- B12 occurs naturally only in animal foods, so vegetarians rely on dairy, eggs, fortified foods or supplements.
- Metformin and acid-reducing drugs (PPIs and H2 blockers) can lower B12 absorption.
- Symptoms range from fatigue to numbness and memory problems, and nerve damage can become permanent if left untreated.
- A blood test, sometimes with follow-up markers like MMA, is the only reliable way to know your status.
Why vitamin B12 matters
Vitamin B12 (cobalamin) helps you make healthy red blood cells, produce DNA and keep your nerves working properly. When you run low, you can develop a type of anaemia with large, poorly working red blood cells, along with nerve and brain symptoms.
Your body stores B12 in the liver, so a deficiency can take years to appear after intake drops. That’s good news for occasional slip-ups, but it also means a problem can creep up unnoticed.
Who is most at risk
Vegetarians
B12 is made by bacteria and is found naturally only in animal foods. Lacto-ovo vegetarians get some from dairy and eggs, but often not enough.
A 2013 review in Nutrition Reviews looked at 18 studies that used sensitive markers of B12 status. It found deficiency was common across vegetarian groups, including 11–90% of older adults studied. Vegans were at higher risk than vegetarians, and so were people who had been vegetarian since birth. The authors recommended preventive steps, including regular supplements.
The wide ranges reflect different populations and tests, but the message is consistent: being vegetarian makes B12 something to plan for, not leave to chance.
People on metformin
Metformin, widely used for type 2 diabetes and prediabetes, can reduce B12 absorption and lower blood levels. This matters because B12 deficiency can cause nerve symptoms that look like diabetic neuropathy. If you take metformin long-term, ask your doctor about periodic B12 checks.
People on acid-reducing medication
B12 in food is bound to protein, and stomach acid helps release it. Proton pump inhibitors (such as omeprazole) and H2 blockers reduce stomach acid. The NIH notes they can impair B12 absorption from food and may lead to deficiency with long-term use.
Others at higher risk
- Older adults, many of whom make less stomach acid
- People with pernicious anaemia, an autoimmune condition that blocks absorption
- People with coeliac disease, Crohn’s disease or past stomach or bowel surgery
For adults over 50, the NIH advises getting most B12 from fortified foods or supplements, which are absorbed more easily than the B12 naturally bound in food.
Symptoms of B12 deficiency
The NHS lists a broad range of symptoms. Many overlap with other conditions, so they’re a reason to get tested rather than to self-diagnose.
| Type | Common symptoms |
|---|---|
| Energy and blood | Tiredness, weakness, breathlessness, palpitations, pale skin, headaches |
| Mouth and gut | Sore or red tongue, mouth ulcers, poor appetite, indigestion or diarrhoea |
| Nerves | Pins and needles or numbness, muscle weakness, poor balance and coordination |
| Brain and mood | Memory or concentration problems, low mood or anxiety, confusion |
| Other | Vision problems |
Two points are worth stressing. First, nerve symptoms can appear without anaemia, so normal haemoglobin doesn’t rule out a deficiency. Second, the NHS warns that the longer a deficiency goes untreated, the greater the risk of permanent damage. If you have tingling, numbness or balance problems, see a doctor soon.
If persistent fatigue is your main complaint, B12 is just one possible cause. Our guide to why you’re always tired after 35 covers others.
How B12 testing works
A standard blood test measures serum B12. According to the NIH, levels below about 200–250 pg/mL are usually considered low. But serum B12 isn’t perfect, and borderline results are common.
If your result is borderline, your doctor may check additional markers:
- Methylmalonic acid (MMA): rises when B12 is low. It’s more specific, though it can also rise with kidney problems.
- Homocysteine: rises with low B12 but also with low folate or poor kidney function, so it’s less specific.
- Full blood count: checks for anaemia and enlarged red blood cells.
- Antibody tests: may be used to check for pernicious anaemia.
Tell your doctor about any supplements you take, including B12 in a multivitamin or B-complex, before the test.
A note on folic acid
High intakes of folic acid can correct the anaemia caused by low B12 without fixing the nerve damage. The NIH notes this led to concerns that folic acid could hide a B12 deficiency. If you take folic acid or a B-complex, make sure your B12 status is checked too.
Food sources for lacto-ovo vegetarians
Dairy and eggs give you some B12. The NIH notes B12 from dairy appears to be more bioavailable than B12 from meat, fish or poultry. Here’s how common foods compare to the 2.4 mcg daily target, using NIH values.
| Food | Serving | B12 (mcg) | % of Daily Value |
|---|---|---|---|
| Nutritional yeast, fortified | ¼ cup | 8.3–24 | 346–1,000% |
| Milk, 2% fat | 1 cup | 1.3 | 54% |
| Yogurt, plain, fat-free | 6 oz (170 g) | 1.0 | 43% |
| Breakfast cereal, fortified (25% DV) | 1 serving | 0.6 | 25% |
| Cheddar cheese | 1½ oz (42 g) | 0.5 | 19% |
| Egg, whole, cooked | 1 large | 0.5 | 19% |
On paper, a glass of milk, a bowl of yogurt and an egg come close to the daily target. In practice, intake varies day to day and absorption drops with age and medication. That’s why many vegetarian men benefit from adding fortified foods or a supplement.
Dairy and eggs are also great protein sources. See our guides to protein after 35 and muscle-building foods for meal ideas.
Fortified foods: read the label
Fortified foods are a reliable vegetarian source because the added B12 is in its free form, which is easy to absorb. Common options include:
- Fortified breakfast cereals
- Fortified nutritional yeast
- Fortified plant milks
Fortification varies by country and brand, so check that “vitamin B12” or “cobalamin” appears on the ingredients list. Unfortified nutritional yeast doesn’t reliably contain B12.
Supplements: forms and dose
The NIH Office of Dietary Supplements sets the Recommended Dietary Allowance (RDA) at 2.4 mcg a day for adult men. No upper limit has been set because B12 has low potential for toxicity.
Supplement doses are often far higher than the RDA. That’s because absorption falls sharply at higher doses. According to the NIH, you absorb about 50% of very small doses (under about 1–2 mcg), but only about 2% of a 500 mcg dose.
Which form?
- Cyanocobalamin: the most common and most studied form, stable and inexpensive.
- Methylcobalamin, adenosylcobalamin and hydroxocobalamin: also available.
The NIH says there’s no evidence that absorption differs by form. It also reports no difference in effectiveness between sublingual tablets and ones you swallow. Pick a form you’ll take consistently.
Typical amounts in products
The NIH notes multivitamins usually contain 5–25 mcg, B-complex products 50–500 mcg, and B12-only supplements 500–1,000 mcg. For treating a diagnosed deficiency, doctors may use injections or high-dose oral B12. A Cochrane review found high-dose oral therapy of 1,000–2,000 mcg worked similarly to injections, though the evidence was low quality. Your dose should come from your doctor based on your test results.
Safety note: B12 has low toxicity, but supplements are not a substitute for diagnosis. See your doctor if you have numbness, tingling, balance problems or memory changes, as nerve damage can become permanent. If you take metformin, acid-reducing drugs or other long-term medicines, ask your doctor or pharmacist about interactions and testing. Don’t stop any prescribed medicine on your own.
A simple B12 plan for vegetarian men
- Include dairy and eggs daily, and add at least one fortified food.
- Consider a supplement, especially if you’re over 50, on metformin or acid reducers, or eat little dairy.
- Ask your doctor for a B12 test, with MMA if borderline, as part of a routine check-up.
- Recheck if symptoms appear or your medications change.
While you’re at it, vitamin D is another nutrient many men run low on. See our guide to vitamin D for men over 35.
FAQ
Can lacto-ovo vegetarians get enough B12 from dairy and eggs?
It’s possible with generous daily intake, but many don’t. Research shows deficiency is common among vegetarians, so fortified foods or a supplement are a sensible backup.
How much vitamin B12 do men need?
The NIH RDA for adult men is 2.4 mcg a day. Supplements often contain much more because only a small fraction of a large dose is absorbed.
Is methylcobalamin better than cyanocobalamin?
The NIH says there’s no evidence that absorption differs by form. Cyanocobalamin is the most researched and usually the cheapest.
Can you take too much B12?
No upper limit has been set because the risk of harm from excess is low. Still, take what your doctor recommends and don’t use high doses to self-treat symptoms without testing.
How long does it take to fix low B12?
It depends on the cause and severity. Many symptoms improve with treatment, but nerve damage may not fully reverse if it’s been present a long time. Your doctor will guide treatment and retesting.
Free tool: get a 7-day vegetarian or vegan high-protein plan from the meal planner.
Sources
- NIH Office of Dietary Supplements – Vitamin B12 Fact Sheet for Health Professionals
- NIH Office of Dietary Supplements – Vitamin B12 Fact Sheet for Consumers
- Pawlak R, et al. How prevalent is vitamin B12 deficiency among vegetarians? Nutr Rev, 2013
- NHS – Vitamin B12 or folate deficiency anaemia: symptoms
- NIH Office of Dietary Supplements – Folate Fact Sheet for Health Professionals
This article is for general education and is not medical advice. Check with your doctor before starting a new training or nutrition plan, especially if you have a health condition.
