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Vitamin B12 and Folate: What You Need to Know

Marie Funk, MS, RD, LDN

Published in Health & Wellness

9 min read

December 21, 2022
a leaf and a tablet of vitamin b12
a leaf and a tablet of vitamin b12

You may have heard that getting plenty of B vitamins in your diet is important, but do you know why?

B vitamins play a key role in many aspects of our health. Vitamin B9 (also called folate) and vitamin B12 are two of these important vitamins, and they’re actually interconnected in many ways.

So what do B vitamins do for your overall health, and how can you include more of them in your diet?

Keep reading to learn:

  • Why vitamin B12 and folate are important
  • How these two vitamins depend on each other to perform their many functions in the body
  • The effect that over or under consuming B vitamins can have on your well-being

What Is Vitamin B12?

Vitamin B12 is one of the most well known of all B vitamins. It’s also sometimes called cobalamin, and it comes in many different forms. Let’s take a deeper look at each form and how much B12 researchers recommend you consume daily.

types of cobalamin vitamin b12

Many B12 supplements come in the cyanocobalamin form. However, there are two active forms of B12. These are known as:

  • Adenosylcobalamin
  • Methylcobalamin 

These are the only forms of vitamin B12 that can be used by the human body. Your body will convert any other form into one of these two active forms of B12.

B12 Recommended Daily Allowance

The recommended daily allowance, or RDA, is the average daily intake of a nutrient that will meet the nutrient requirements of most healthy individuals. The RDA of vitamin B12 is measured in micrograms (mcg). 

Here’s how much vitamin b12 medical professionals advise you to consume per day.

recommended daily intake of b12 chart

What is Folate?

Folate is another B group vitamin, also called vitamin B9. Folic acid is the term used for the form of folate found in fortified foods and most supplements. Folate refers to the form naturally found in food and biological tissues.

Folate bioavailability from food, or the amount of a substance that can actually be used or absorbed by the body, ranges from about 10 percent to 98 percent depending on different factors. Folic acid tends to be more readily absorbed than folate. 

Folate RDA 

The RDA of folate is measured in micrograms of dietary folate equivalents, abbreviated as mcg DFE. DFEs reflect the higher bioavailability of folic acid than that of folate from food.

Around 85 percent of folic acid is estimated to be bioavailable if taken with food, and only 50 percent of folate that is naturally present in food is bioavailable. So, 1 mcg DFE is equal to:

  • 1 mcg of folate from food
  • 0.6 mcg of folic acid from fortified foods or dietary supplements consumed with food
  • 0.5 mcg of folic acid from dietary supplements taken on an empty stomach

Here’s how to make sure you’re getting enough folate:

recommended daily intake of folate chart

How Vitamin B12 and Folate Affect Your Health

B vitamins are necessary for a number of functions in the body. When it comes to vitamin B12 and folate, the pair both support:

  • Formation of red blood cells
  • Brain and nerve cell health
  • DNA production
  • Methylation, which is a biochemical reaction in the body that happens when a methyl group is added to DNA, proteins, or other molecules. These reactions affect how some molecules act in the body.

Both folate and B12 are needed for pregnancy and fetal development, though folate is in higher demand. Inadequate dietary intake of folate is linked to spina bifida, a birth defect in the spine, and anencephaly, a birth defect in the brain. 

This is why the U.S. Food and Drug Administration requires that folic acid be added to most enriched breads, flours, cornmeal, pastas, rice, and other grain products, along with iron and other micronutrients.

Since this decision in 1998, neural tube birth defects have dropped by 28 percent. 

Deficiencies in B12 and Folate

a plate of broccoli and brussels sprouts

Deficiencies in both vitamin B12 and folate can cause serious health problems. Deficiencies in both nutrients have been studied for their possible implications in cardiovascular disease, cancer, dementia, and depression.

Vegans and vegetarians may be at a higher risk for being deficient in vitamin B12. Having low vitamin B12 levels can lead to fatigue, mouth ulcers, and other neurological side effects.

Some other shared symptoms of B12 and folate deficiency are:

  • Megaloblastic anemia, which is a condition of larger than normal red blood cells, and a smaller than normal amount. This can cause fatigue, weakness, difficulty concentrating, irritability, headaches, heart palpitations, and shortness of breath. 
  • Neurological changes
  • Dementia
  • Weight loss
  • Problems with infertility and/or fetal developmental abnormalities

Vitamin B12 deficiency may also cause glossitis, or inflammation, of the tongue and nerve damage with numbness and tingling in the hands and legs. It can also lead to changes in methylation patterns, which can affect a person’s risk of developing diseases like cancer.

Low levels of folate may also cause changes in the hair, skin, and fingernail pigmentation, as well as shallow sores or ulcers on the tongue and mouth. It usually coexists with other nutrient deficiencies because it’s strongly associated with poor diet, alcoholism, and malabsorptive disorders. 

Who is At Risk for B Vitamin Deficiency?

someone holding a pack of vitamins

People at risk for both a vitamin B12 deficiency and a folate deficiency include:

  • People who have alcohol use disorder or a chronic high consumption of alcohol
  • People with GI disorders, such as malabsorption disorder
  • People taking certain medications, like GERD medications and metformin (vitamin B12), and methotrexate and certain anti-seizure medications (folate)

Folate Deficiency Risk Factors

People at risk for folate deficiency include:

  • People who are pregnant or trying to become pregnant
  • People with zinc deficiency, because zinc is needed for folate absorption

People with genetic polymorphism in the methylenetetrahydrofolate reductase gene, or MTHFR, have a reduced ability to convert folate to its active form. This is because the MTHFR enzyme needed for this conversion is less active.

Research on the benefits of folate supplements for people with this genetic polymorphism is inconclusive. Researchers suggest increasing your folate through ingestion of foods that contain 5-MTHF, like kale, spinach, arugula, and swiss chard.

B12 Deficiency Risk Factors

People at risk for B12 deficiency include:

  • People who follow a plant-based diet, like veganism or vegetarianism
  • People with pernicious anemia, a type of anemia that arises from the inability to absorb B12. Many people with pernicious anemia are treated with lifelong intramuscular vitamin B12 replacement or oral vitamin B12 replacements of one milligram per day. 
  • People with inadequate stomach acid or who take medications that cause decreased stomach acid, like those for GERD
  • People taking metformin, a treatment for diabetes that can reduce the absorption of vitamin B12

It’s important to note that there is currently no evidence that people without a deficiency in B vitamins will benefit from supplementation. Always talk to your doctor before taking supplements. 

Testing for B12 and Folate

a doctor holding a vial of blood

If you want to test your vitamin B12 or folate levels, you should consult your doctor. Checking your levels can be especially helpful if you

  • Have anemia
  • Have an eating disorder
  • Have an autoimmune diseases
  • Have a history of glossitis or mouth ulcers
  • Have a history of peripheral neuropathy
  • Have a malabsorption syndromes
  • Take certain medications, including metformin, proton pump inhibitors, and oral contraceptives
  • Follow a diet low in animal-sourced foods, like veganism or vegetarianism
  • Have chronic fatigue syndrome
  • Have an abnormal blood count
  • Are pregnant

Blood tests are used by medical professionals to detect deficiencies of these vitamins in the body. However, research shows that testing vitamin B12 blood serum levels may not be the most accurate test for a B12 deficiency. Instead, you may be given a methylmalonic acid (MMA) test.

A folate deficiency test may be done as a blood serum test or a red blood cell folate test, though some researchers believe a serum test is more accurate. Consult with your doctor to determine the right test for you.

B12 and Folate Toxicity

a man caring for a woman who is laying down

Toxic effects of vitamin B12 are very rare. No adverse effects have been associated with large intakes of B12 from food or supplements in healthy people. In the same way, no adverse effects have been associated with large intakes of folate from food. 

There are concerns regarding safety and toxicity when it comes to excess synthetic folic acid intake from supplemental folic acid. High folic acid intakes could accelerate the progression of precancerous lesions, which raises the risk of colorectal and other cancers in some people. 

Both vitamin B12 and folate deficiencies are associated with megaloblastic anemia. Large doses of folic acid (typically five milligrams or above) given to a person with undiagnosed vitamin B12 deficiency may help treat this condition without correcting the B12 deficiency.

For this reason, the researchers advise that all adults limit their intake of folic acid to one milligram daily, including both supplements and fortified foods. 

Vitamin B12 and Folate Food Sources

Food sources of vitamin B12 include:

a list of food sources of vitamin b12
  • Fish and shellfish
  • Organ meats like liver
  • Red meat
  • Eggs
  • Poultry
  • Dairy products like milk, cheese, and yogurt
  • Fortified foods like some breakfast cereals
  • Fortified nutritional yeast 

Food sources of folate include:

a list of food sources of folate
  • Dark green leafy vegetables, like turnip greens, spinach, romaine lettuce, asparagus, Brussels sprouts, and broccoli
  • Beans
  • Peanuts
  • Sunflower seeds
  • Fresh fruits and fruits juices
  • Whole grains
  • Liver
  • Egg yolks
  • Seafood
  • Fortified foods like some breakfast cereals

Supplemental B12 and Folate

As mentioned earlier, excessive intakes of vitamin B12 and folate may cause health problems in some cases. Always talk to your qualified healthcare provider before taking any new supplements.

They can test for deficiencies, recommend appropriate doses, or advise ways to get these nutrients from your diet. 

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Heather Davis, MS, RDN, LDN

Reviewed by: Heather Davis, MS, RDN, LDN

Heather is a Registered and Licensed Dietitian Nutritionist (RDN, LDN), subject matter expert, and technical writer, with a master's degree in nutrition science from Bastyr University. She has a specialty in neuroendocrinology and has been working in the field of nutrition—including nutrition research, education, medical writing, and clinical integrative and functional nutrition—for over 15 years.