A salmon fillet poaching in a stainless steel pan with dill sprigs and lemon slices in the broth.

Vitamin B12 and Energy: When Extra B12 May Not Help

The Dose Analysis

Does vitamin B12 give you energy? Only in a narrow sense. Your body needs B12 to turn food into energy, and low B12 can cause tiredness, so correcting a true shortfall matters. But the NIH Office of Dietary Supplements (ODS) says B12 supplements appear to have no beneficial effect on performance when there is no nutritional deficit. So extra B12 does not appear to improve performance when your B12 status is already normal. Ongoing tiredness has many causes and is worth a check with a clinician.

Key takeaways

  • The NIH ODS says vitamin B12 supplements appear to have no beneficial effect on performance in people who are not deficient.
  • Low B12 can cause fatigue, and the ODS lists older adults, vegans and vegetarians, and people taking acid reducers or metformin among those more likely to run low. A blood test, not a supplement, shows your status.
  • A B-complex label lists several vitamins with upper limits, such as folic acid and vitamin B6. Add up every product you take before adding another.

Why B12 is linked with energy

Vitamin B12 helps form red blood cells, keeps nerve cells working and is needed to make DNA. It also works with enzymes in energy metabolism, which is why it is often promoted as an energy enhancer. The NIH ODS fact sheet makes that link itself, then adds the key point: B12 supplementation appears to have no beneficial effect on performance in the absence of a nutritional deficit.

In other words, B12 is a nutrient your body must have, and the benefit the ODS describes comes from fixing a shortfall. The ODS also notes that the body stores about 1 to 5 milligrams of B12, about 1,000 to 2,000 times what people typically eat in a day. That is why a shortfall can take years to show up.

When low B12 can make you tired

The picture changes when B12 really is low. The ODS lists fatigue among the signs of B12 deficiency, along with anemia, pale skin, a sore tongue, palpitations and nerve changes such as numbness and tingling in the hands and feet. It notes that the nerve symptoms can occur without anemia, so early diagnosis matters.

The ODS names several groups who are more likely to run low:

  • Older adults: between 3% and 43% of older adults living in the community have low B12 levels, depending on the definition used, according to the ODS. Atrophic gastritis, which reduces stomach acid and a protein called intrinsic factor, affects 8% to 9% of adults age 65 and older and lowers B12 absorption from food.
  • People who eat few or no animal foods: B12 occurs naturally only in animal foods, so vegans and vegetarians have a higher risk. The ODS says fortified foods and supplements can substantially reduce that risk.
  • People taking certain medicines: the ODS says acid reducers (proton pump inhibitors such as omeprazole and H2 blockers such as cimetidine) can interfere with B12 absorption from food, and metformin might lower B12 levels.
  • People with pernicious anemia or stomach or bowel conditions or surgery, which can block absorption even when intake is adequate.

If you are in one of these groups, or you have symptoms like those above, ask a clinician about a blood test. The ODS says a serum B12 test is the usual starting point, and a marker called methylmalonic acid can confirm a borderline result.

How much B12 adults need, and how much is absorbed

The Food and Nutrition Board sets the adult Recommended Dietary Allowance (RDA) at 2.4 mcg a day, and the NIH ODS lists it. The Daily Value used on U.S. labels is also 2.4 mcg. B12 has no tolerable upper intake level, because the ODS describes it as generally considered safe, even at high doses.

That is why B12 supplements can show very large percent Daily Values. A big number on the label is not the amount your body takes in. According to the ODS, absorption is about 50% at doses of 1 to 2 mcg, but only about 2% at 500 mcg and 1.3% at 1,000 mcg. The ODS gives no figure for larger doses. It also says no evidence shows that absorption varies by form, whether cyanocobalamin, methylcobalamin, adenosylcobalamin or hydroxycobalamin.

The NIH ODS lists the B12 content of these selected foods:

Food B12 per serving
Beef liver, cooked, pan fried, 3 ounces 70.7 mcg
Clams (without shells), cooked, 3 ounces 17 mcg
Oysters, eastern, wild, cooked, 3 ounces 14.9 mcg
Nutritional yeast, fortified, about 1/4 cup (check label) 8.3 to 24 mcg
Salmon, Atlantic, cooked, 3 ounces 2.6 mcg
Tuna, light, canned in water, 3 ounces 2.5 mcg
Beef, ground, 85% lean, pan browned, 3 ounces 2.4 mcg
Milk, 2% milkfat, 1 cup 1.3 mcg
Yogurt, plain, fat free, 6-ounce container 1.0 mcg
Breakfast cereal fortified with 25% of the DV, 1 serving 0.6 mcg
Cheese, cheddar, 1 1/2 ounces 0.5 mcg
Egg, whole, cooked, 1 large 0.5 mcg
Turkey, breast meat, roasted, 3 ounces 0.3 mcg
Tempeh, 1/2 cup 0.1 mcg
Banana, 1 medium 0 mcg
Bread, whole wheat, 1 slice 0 mcg
Strawberries, raw, halved, 1/2 cup 0 mcg
Beans, kidney, boiled, 1/2 cup 0 mcg
Spinach, boiled, drained, 1/2 cup 0 mcg

How to read a B-complex label

Most "energy" B12 products are B-complex formulas, so the B12 line is only one row to read. Energy+™ is an example. Its Supplement Facts list, per 2-capsule serving: vitamin C 150 mg; thiamin (B1) 100 mg; riboflavin (B2) 100 mg; niacin 20 mg NE (as niacinamide); vitamin B6 30 mg; folate 1,190 mcg DFE (as 700 mcg folic acid); vitamin B12 2,000 mcg (as cyanocobalamin); biotin 1,000 mcg; pantothenic acid 100 mg; choline 100 mg; and inositol 150 mg. The B12 line shows 83,333% of the Daily Value. The suggested use is two capsules once a day, with food and an 8 fl oz glass of water, or as directed by your healthcare professional. No study cited here tested this product, and its B12 amount is above the largest dose for which the ODS gives an absorption figure.

The label caution reads: "Do not exceed recommended dose. Pregnant or nursing mothers, children under the age of 18, and individuals with a known medical condition should consult a physician before using this or any dietary supplement." The label also says: "Keep out of reach of children. Do not use if safety seal is damaged or missing. Store in a cool, dry place." Its product page adds: "If you take medication, talk with your healthcare provider before starting any new supplement."

Add it up before you stack products

B12 has no upper limit, but other vitamins in a B-complex do. If you also take a multivitamin, another B-complex or fortified foods, add the totals. These are the adult upper limits (ULs) listed by the NIH ODS, compared with one serving of Energy+:

  • Folic acid: 700 mcg per serving. The ODS lists an adult UL of 1,000 mcg a day for folic acid from supplements and fortified foods. The ODS folate fact sheet also notes that large amounts of folate can correct the anemia of B12 deficiency, but not the nerve damage, and might worsen the anemia and thinking problems linked to low B12.
  • Vitamin B6: 30 mg per serving. The ODS lists an adult UL of 100 mg a day from food and supplements. The European Food Safety Authority set a lower adult UL of 12 mg a day in 2023, based on nerve damage (peripheral neuropathy). One serving of Energy+ alone is above the EFSA figure.
  • Niacin: 20 mg NE per serving. The ODS lists an adult UL of 35 mg a day that applies to niacin from supplements, not food.
  • Vitamin C: 150 mg per serving. The ODS lists an adult UL of 2,000 mg a day from food and supplements.
  • Choline: 100 mg per serving. The ODS lists an adult UL of 3,500 mg a day from food and supplements.
  • Biotin: 1,000 mcg per serving. Biotin has no UL, but the ODS biotin fact sheet warns that intakes above recommended amounts can cause falsely high or falsely low lab test results. Tell your clinician you take biotin before any blood test.

Medicines and other cautions

The NIH ODS fact sheets name medicines that interact with nutrients in a formula like this one:

  • Vitamin B12: acid reducers and metformin can lower B12 levels.
  • Folate: folate supplements can interact with methotrexate, with antiepileptic drugs such as phenytoin, carbamazepine and valproate, and with sulfasalazine.
  • Vitamin B6: the ODS names the tuberculosis antibiotic cycloserine, antiepileptic drugs such as valproic acid, carbamazepine and phenytoin, and the lung medicine theophylline.
  • Niacin: the ODS names the tuberculosis medicines isoniazid and pyrazinamide.
  • Biotin: anticonvulsants such as carbamazepine, primidone, phenytoin and phenobarbital have been linked with lower biotin levels.
  • Vitamin C: people having chemotherapy or radiation should consult their oncologist before taking vitamin C or other antioxidant supplements. Vitamin C with other antioxidants may reduce the rise in HDL cholesterol from combined niacin and simvastatin therapy, and the ODS says health care providers should monitor lipid levels in people taking both statins and antioxidant supplements.

If you take any of these, or any regular medicine, talk with your healthcare provider before use.

If you are pregnant, nursing or trying to conceive, ask your healthcare provider before use.

Frequently asked questions about vitamin B12 and energy

Will B12 give me energy if my levels are normal?

The NIH Office of Dietary Supplements does not report that it does. It says B12 supplementation appears to have no beneficial effect on performance when there is no nutritional deficit. If you think your B12 may be low, a blood test is the way to find out.

How do I know if my B12 is low?

A blood test ordered by a clinician. The NIH ODS says a serum B12 level is the usual test, and methylmalonic acid can confirm a borderline result. Fatigue alone does not show that B12 is the cause, because many things cause tiredness.

Who is most likely to be low in B12?

The NIH ODS lists older adults, people with pernicious anemia or stomach or bowel conditions or surgery, vegans and vegetarians, and people who take acid reducers or metformin for a long time.

Is a high-dose B12 supplement safe?

The NIH ODS says B12 has no tolerable upper intake level because it is generally considered safe, even at high doses. A B-complex also contains other vitamins that do have upper limits, such as folic acid and vitamin B6, so add up every product you take.

Is cyanocobalamin or methylcobalamin better absorbed?

The NIH ODS says no evidence indicates that absorption rates of B12 in supplements vary by form. Absorption depends far more on the dose: about 50% at 1 to 2 mcg, and about 2% at 500 mcg.

Related reading

Sources

The Dose Analysis and CuraMyHealth are both operated by Hofer LLC. Purchases linked from our reviews take place on CuraMyHealth.

This article is for education and is not personal medical advice. A qualified healthcare professional can help assess your needs and review the specific formula. Individual results vary.

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.

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