Vitamin B12 is essential for healthy blood and nerve cells, as well as making DNA and turning food into energy. While most adults need 2.4 mcg per day, the B12 demands can increase in certain situations. The question is, how much B12 should you take a day? Here are the answers.
B12 absorption affects how much B12 you need
B12 absorption follows a multi-step process:
- B12-containing food (like beef, poultry, fish, eggs, yogurt and cheese) arrives your stomach
- Acid extracts B12 from the food
- The free B12 moves into the alkaline environment of the intestine
- B12 attaches to a protein called intrinsic factor
- Intrinsic factor transports B12 to cells in the intestinal lining
- Those cells take B12 into circulation in the bloodstream for distribution
If any step in this process is missing, you do not absorb B12. Without stomach acid, you can’t extract B12 from food and it never makes it to the intestine to await transport. Without intrinsic factor, B12 does not enter circulation.
What determines B12 need?
Your body’s ability to complete those six steps affect how much B12 you absorb from food, thus how much your doctor may recommend you supplement.
Low stomach acid
Stomach acid and intrinsic factor production decline with age.
More than 20% of older adults are deficient in B12. About 30% of adults over age 51 have atrophic gastritis, which causes low stomach acid secretion and low intrinsic factor production, putting them at risk for poor B12 absorption from food.
Acid blockers and proton pump inhibitors comprise the second largest number of prescriptions filled each year. They block stomach acid production. Too little or no stomach acid means inability to extract B12 from food, thus low B12. These drugs are known to deplete B12.
Gastric bypass surgery reduces the amount of stomach acid produced. Patients don’t absorb B12 and are at severe risk for deficiency. With about 18% of patients scheduled for bariatric surgery deficient in B12, it should be no surprise that the percentage rises to 19–35% five years after surgery.
Medication use
In studies on B12 and women taking oral contraceptives, researchers found that the binding capacity of the serum used to measure B12 levels was lower than nonusers of oral contraceptives as were those of a protein that protects B12 from stomach degradation. However, neither is proven to be the definitive reason why oral contraceptives are correlated with lower B12 levels.
Antibiotics may disrupt the intestinal bacteria needed for proper absorption, and use of these drugs is often correlated with depleted B12.
Anti-gout, anticonvulsants, cholesterol, psychiatric, and diabetes medications also interfere with B12 absorption.
Sometimes not only do medications interfere with B12, but B12 interferes with the medications as well. Many people opt to take medications and supplements at different times of day.
Digestive issues
Conditions in the intestines, like Crohn’s and celiac, can interfere with B12 absorption. Rates of B12 deficiency are higher in people with celiac than the general population.
Pernicious anemia
This rare blood disorder is believed to be caused by an autoimmune condition that inhibits intrinsic factor production. Though only occurring in about 1% of the population, it’s responsible for up to 50% of B12 deficiency in adults.
PREGNANCY OR BREASTFEEDING
B12 requirements increase slightly to 2.5 mcg and 2.8 mcg, respectively, for pregnant and breastfeeding women. B12 deficiency during pregnancy is linked to serious birth defects, and during lactation can cause B12 deficiency in the baby.
Vegetarian and vegan diets
B12 only occurs naturally in animal foods. People following vegan and vegetarian diets must rely on fortified plant-based foods to reach the 2.4 mcg needed in a day.
What foods have B12?
According to studies, B12 bioavailability (the amount your body can use) is higher in dairy sources than in meats, poultry, and fish. Fortified plant foods also contain bioavailable B12.
- Beef
- Shellfish
- Fish
- Nutritional yeast
- Yogurt
- Milk
- Fortified breakfast cereals
How much B12 do supplements provide?
B12 supplements typically contain anywhere between 5 mcg (in a multivitamin) and 3,000 mcg in a gummy.
Doses are higher in supplements because of the B12 absorption challenges mentioned at the beginning of this article. In healthy people, only about 10 mcg of a 500 mcg traditional oral supplement is absorbed.
B12 is water-soluble, so any extra you don’t absorb is flushed out of your body without risk of overdosing.
What to look for in a B12 supplement
Supplements already contain B12 in its free form, so you are not reliant on stomach acid for absorption. However, you still need enough intrinsic factor to absorb B12 from supplements.
This puts a premium on absorption.
Look for bioavailable forms of B12
Methylcobalamin is a usable for most people. Cyanocobalamin is well-studied and often used to keep Methylcobalamin stable.
Use a B Complex
Often, factors that deplete B12 also deplete other B vitamins. A B Complex offers all the B vitamins in one.
Consider liposomal B12
Often, people who have difficulty producing intrinsic factor are prescribed intravenous B12, which bypasses the intestinal transport by injecting B12 directly into the bloodstream.
Liposomal encapsulated B12 may also bypass these compromised absorption pathways in an easy-to-take oral supplement. Liposomes are tiny phospholipid spheres that carry the B12 from the digestive system into the bloodstream for absorption in the cells.
Summary
While the RDA says most of us need 2.4 mcg per day, tracking B12 consumption is challenging and depends on many factors. Certain life situations, diets, and absorption challenges determine B12 demands and the need for supplements.
Frequently asked questions
Is 2.4 mcg the same as 1000 mcg?
No. 1000 mcg is equivalent to 1 mg.
What is the recommended daily dosage of B12 supplements?
The RDA for most adults is 2.4 mcg per day.
Is it okay to take 5000 mcg of B12 daily?
Since B12 is water soluble and the body can’t store it, high doses are generally considered safe. However, extremely high doses are best taken under a doctor’s supervision.
