Vitamin B12 is a water-soluble nutrient that’s required for many crucial processes in your body.

The ideal dose of vitamin B12 varies based on your gender, age and reasons for taking it.

This article examines the scientific evidence behind recommended dosages for B12 for different people and uses.

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Vitamin B12 is an essential nutrient that plays a critical role in several of your body’s processes.

It’s necessary for proper red blood cell production, DNA formation, nerve function and metabolism (1).

Vitamin B12 also plays a key role in breaking down homocysteine, an amino acid that, in high levels, has been linked to chronic conditions like heart disease, stroke and Alzheimer’s (2).

Additionally, vitamin B12 is important for energy production. However, there’s currently no evidence that taking B12 supplements increases energy levels in people who are not deficient in this nutrient (3).

Vitamin B12 is found mostly in animal products, including meats, seafood, dairy products and eggs. It’s also added to some processed foods, such as cereal and non-dairy milk.

Because your body can store B12 for several years, serious B12 deficiency is rare, but up to 26% of the population may have a mild deficiency. Over time, B12 deficiency can lead to complications like anemia, nerve damage and fatigue.

Vitamin B12 deficiency can be caused by not getting enough of this vitamin through your diet, problems with absorbing it or taking a medication that interferes with its absorption (4).

The following factors may put you at a higher risk of not getting enough vitamin B12 from diet alone (5, 6):

  • Following a vegetarian or vegan diet
  • Being over 50 years old
  • Gastrointestinal disorders, including Crohn’s disease and celiac disease
  • Surgery on the digestive tract, such as weight loss surgery or bowel resection
  • Metformin and acid-reducing medications
  • A type of anemia called pernicious anemia
  • Specific genetic mutations, such as MTHFR, MTRR and CBS
  • Regular consumption of alcoholic beverages

If you’re at risk of deficiency in this critical nutrient, taking a supplement may help you meet your needs.

Summary Vitamin B12 is an important nutrient that plays a critical role in your body. It’s mainly found in animal products, and some may be at risk of not getting enough from diet alone.

The recommended daily intake (RDI) for vitamin B12 for people over 14 is 2.4 mcg (1).

However, you may want to take more or less, depending on your age, lifestyle and specific situation.

Note that the percent of vitamin B12 your body can absorb from supplements is not very high — it’s estimated that your body only absorbs 10 mcg of a 500-mcg B12 supplement (7).

Here are some recommendations for B12 dosages for specific circumstances.

Adults Under Age 50

For people over 14, the RDI for vitamin B12 is 2.4 mcg (1).

Most people meet this requirement through diet.

For example, if you ate two eggs for breakfast (1.2 mcg of B12), 3 ounces (85 grams) of tuna for lunch (2.5 mcg of B12), and 3 ounces (85 grams) of beef for dinner (1.4 mcg of B12), you would consume more than double your daily B12 needs (1).

Therefore, supplementing with B12 is not recommended for healthy people in this age group.

However, if you have any of the factors described above that interfere with vitamin B12 intake or absorption, you may want to consider taking a supplement.

Adults Over Age 50

Older people are more susceptible to vitamin B12 deficiency. While relatively few younger adults are deficient in B12, up to 62% of adults over the age of 65 have less than optimal blood levels of this nutrient (8, 9).

As you age, your body naturally makes less stomach acid and intrinsic factor — both of which can impact the absorption of vitamin B12.

Stomach acid is necessary to access the vitamin B12 found naturally in food, and intrinsic factor is required for its absorption.

Due to this increased risk of poor absorption, the National Academy of Medicine recommends that adults over the age of 50 meet most of their vitamin B12 needs through supplements and fortified foods (1).

In one eight-week study in 100 older adults, supplementing with 100–500 mcg of vitamin B12 were found to normalize B12 levels in 75–85% of participants. Higher doses of up to 1,000 mcg (1 mg) may even be necessary for some (10).

Pregnant Women

Pregnant women have slightly higher vitamin B12 needs than the general population.

Low maternal levels of this vitamin have been associated with birth defects in infants (11).

Additionally, a large systematic review showed that B12 deficiency is associated with a higher risk of premature birth and low birthweight in newborns (12).

Therefore, the RDI for vitamin B12 during pregnancy is 2.6 mcg. This level can be met through diet alone or with a prenatal vitamin (1).

Breastfeeding Women

Vitamin B12 deficiency in breastfed infants has been linked to developmental delay (13).

Additionally, B12 deficiency in infants can lead to irritability, decreased appetite and failure to thrive (14).

For these reasons, the RDI for this vitamin for breastfeeding women is higher than that for pregnant women — namely 2.8 mcg (1).

Vegetarians and Vegans

Vitamin B12 recommendations do not differ for people following a plant-based diet.

However, the RDI of 2.4 mcg for people under 50 years of age is much harder to meet on a vegetarian or vegan diet (1).

In a review of 40 studies on vitamin B12 in vegetarians, up to 86.5% of vegetarian adults — including older adults — were found to have low levels of vitamin B12 (15).

There are currently no government recommendations for B12 supplement dosages for vegetarians.

However, one study suggests that doses up to 6 mcg of vitamin B12 per day may be appropriate for vegans (16).

B12 for Improved Energy

Though vitamin B12 is commonly taken to increase energy levels, evidence showing that B12 supplements have a positive effect on energy in people without a deficiency is lacking.

However, B12 supplements have been found to improve energy levels in those who are deficient in this nutrient (17).

One review recommended 1 mg of vitamin B12 daily for a month in those with vitamin B12 deficiency, followed by a maintenance dose of 125–250 mcg per day (18).

People who have issues absorbing vitamin B12, such as those with Crohn’s disease or other gastrointestinal issues, may benefit from B12 injections, which bypass the need for absorption by the digestive tract (17).

B12 for Memory and Mood

It’s commonly thought that taking vitamin B12 can boost your memory and mood. However, there’s not a lot of scientific evidence to back up this theory.

Animal studies have suggested that vitamin B12 deficiency has been associated with memory impairment. Yet, there’s currently no evidence that B12 supplements improve memory in humans (19).

In a large review, vitamin B12 supplements had no impact on depressive symptoms in the short term but may help prevent relapse over the long term (20).

There are no specific dose recommendations for B12 supplements for mental performance or mood.

Summary Optimal dosing of vitamin B12 varies based on age, lifestyle and dietary needs. The general recommendation for adults is 2.4 mcg. Older adults, as well as pregnant and breastfeeding women, require higher doses.

Vitamin B12 is a water-soluble vitamin, meaning that your body excretes what you don’t need in your urine.

Because it’s relatively safe, no tolerable upper intake level (UL) has been set for vitamin B12. UL is considered the maximum amount of a substance that can be taken safely without side effects.

However, vitamin B12 has been shown to cause rare side effects in some cases.

Vitamin B12 injections may lead to skin conditions, such as acne and dermatitis (rash) (21).

High doses of B vitamins over 1,000 mcg have also been associated with complications in people with kidney disease (22).

Furthermore, extremely high blood levels of B12 in mothers was connected to a higher risk of autism in their children (23).

Summary Though high doses of vitamin B12 supplements have been linked to rare side effects in certain populations, it’s generally safe, and there’s currently no recommended maximum amount for this vitamin.

Vitamin B12 is a nutrient that plays many essential roles in your body.

The RDI for vitamin B12 ranges from 2.4 mcg for adults to 2.8 mcg for breastfeeding women.

Most people meet these needs through diet alone, but older adults, people on strict plant-based diets and those with digestive disorders may benefit from supplements, though dosages vary based on individual needs.