What's The Difference Between Active and Inactive Vitamin B12? And Why Does It Matter?

By Brandi Black, RHN

What's The Difference Between Active and Inactive Vitamin B12? And Why Does It Matter?

August 2, 2019 - Active and inactive vitamin B12 are found in different plant and animal sources. Learn about their differences and how these differences affect nutrient absorption levels.

Since B12 is essential for so many functions in the body, deficiency can present itself in numerous ways. However, since B12 deficiency shares similar symptoms with other ailments, it’s not uncommon for vitamin B12 deficiency to go unnoticed. 

Why B12 is So Important For Your Health

As suggested above, vitamin B12 is involved in many bodily functions that keep you feeling well on a daily basis. But B12 has many other functions that keep you healthy “behind the scenes.” B12 works with folic acid (folate or vitamin B9), to form red blood cells and synthesize DNA (1). Both vitamin B12 and B9 are also crucial for a healthy functioning nervous system. Together, they help control nerve impulses and create “insulation” around our nerves as protection (this is also known as the myelin sheath).

The myelin sheath is an integral part of the nervous system, as it allows messages to be transmitted from the brain to the correct body part (2). 

Other Symptoms of B12 Deficiency May Include: Pale skin Loss of appetiteNumbness and cramping in arms and legs

Vitamin B12 Deficiency: Not Just a Vegan and Vegetarian Issue

Until recently, vitamin B12 deficiency was thought to primarily affect vegans and vegetarians because fish, eggs and organ meats are the richest sources of B12. Such deficiency is also a concern among the elderly who produce less stomach acid, which is needed to efficiently absorb B12 (3). 

But what we thought we knew about vitamin B12 deficiency may not be true. Research suggests more individuals than previously thought may have low vitamin B12 levels— and those affected may be completely unaware. 

One reason this occurs is because serum lab tests often show normal B12 levels, when their levels may actually be low. Several factors can influence the test and produce inaccurate results, such as the use of oral contraceptives, recent food intake, pregnancy, low folic acid levels and genetic factors. Some people may also get false normal test results based on where vitamin B12 is being stored in their body— which can raise serum B12 levels. 

At present time, the most accurate method of testing for vitamin B12 deficiency is said to be the methylmalonic acid test (4). The methylmalonic acid test measures the activity of an enzyme called methylmalonyl-COA, which requires vitamin B12 for energy production. When B12 levels are low, the enzyme’s overall activity is reduced, which leaves methylmalonyl acid build up in the blood and indicates deficiency. 

Another option for B12 testing is the Holotranscobalamin II (or holotc) test which is said to be less impacted by genetic factors or pregnancy, but is still being tested for accuracy (5). 

Some of us may not realize we’re deficient because we’re eating foods that contain a form of vitamin B12 that’s not useable by the body: inactive vitamin B12. 

What’s The Difference Between Active and Inactive Vitamin B12, And Why Does It Matter?

When you have a vitamin or mineral deficiency, it would seem logical to correct the deficiency by increasing the foods that contain the nutrients you need. Unfortunately, when it comes to correcting a B12 deficiency, it’s not that simple.

You see, there are two forms of vitamin B12 that exist in food sources: active and inactive B12. But what’s the difference between the two, and more importantly, how do these differences affect absorption rates?

Active B12 is the form of B12 your body can digest, absorb and utilize right away, and it’s found abundantly in animal-source based foods such as fish, organ meats and milk. This is the form of B12 your body needs to produce energy, and keep your nerves and red blood cells healthy. 

Inactive B12 may be found in plant foods, such as seaweed, spirulina and nutritional yeast. This form of B12 may be poorly absorbed in the small intestine, which is why B12 deficiency is a concern for those who avoid animal foods (6).

But aside from being poorly absorbed there may be an even bigger problem with having too much inactive B12 in your diet. 

Researchers found that the inactive form of B12 may actually interfere with the body’s ability to use active B12. This means it’s possible for those who include animal-source based foods in their diet to still become vitamin B12 deficient if they’re eating foods that contain inactive B12 with active B12 sources (7). 

Research and table Courtesy of veganhealth.org  


Micrograms (µg) of B12 Analogue Given

B12 Food Source





Spirulina, Nori




Spirulina, Nori












Sourdough Bread, Barley, Kombu, Barley Malt Syrup


Non Vegans


1.5 / 0.5

Algae / Fish & Milk












Fish, Milk




Fish, Nori




Supplements, Fish, Nori


MCV= Mean Corpuscular Volume

When two sources of inactive B12 were eaten together, B12 levels became worse. But when algae (higher inactive B12), fish (higher in active B12) and milk (higher in active B12) were eaten together, B12 levels improved. This suggests that two sources of active B12 may outweigh the negative effects of its inactive counterpart.

On the other hand, when one food source of inactive B12 (nori seaweed) was eaten with one food source of active B12 (fish), B12 levels worsened. This suggests that if a food source contains a higher level of inactive B12 vs. a food that contains active B12, it can cancel out the active B12 of a food and prevent the body from using it at all— hence being referred to as “useless.”

Think of it this way: imagine that active B12 is fire, and inactive B12 is water. A few drops of water won’t put out a fire, but several buckets of water will “cancel” the fire out. 

Foods That Contain Active Forms of Vitamin B12

The active forms of vitamin B12 are coenzymes, which can convert to a form of usable B12 in the body: methylcobalamin, adenosylcobalamin, hydroxocobalamin and cyanocobalamin (a synthetic form of vitamin B12 found in supplements). 

The foods that have been shown to contain active B12 include: 

Organ meats (beef liver)
Cottage Cheese 

As you can see, most foods that contain active B12 are from animal sources, while most plant foods such as spirulina, grains such as barley and sourdough, and seaweeds such as nori and kombu, have been shown to contain higher levels of inactive B12. If you’ve chosen to follow a vegan or vegetarian diet, you’re likely wondering how you’re supposed to get enough active B12 then. Fortunately, there’s one plant food that’s been proven to contain an absorbable form of active B12, and may improve vitamin B12 levels in the blood: the amazing green superfood, chlorella! 

Chlorella: One of The Only Plant Foods to Contain Active B12

As one of the rare plant foods to contain Active B12, chlorella is an ideal superfood for vegans and vegetarians to add to their diets each day. In fact, one study published in The Journal of Medicinal Food observed healthy vegans and vegetarians had low B12 levels before taking chlorella—the results were promising.

This study’s participants were given supplements of chlorella pyrenoidosa (the strain of chlorella found in Sun Chlorella tablets, granules and powder) for 60 days. Results showed those who received 9g of Sun Chlorella each day had a significant reduction in their homocysteine levels and MMA levels— both of which indicate a B12 deficiency when elevated.

Absorption and bioavailability are important factors when taking supplements— especially chlorella. The reason why Sun Chlorella is able to raise B12 levels, is likely due to the unique processing method it uses, which allows chlorella’s nutrients to become highly digestible and readily absorbed by the body.

Some chlorella processing produce chlorella that is poorly digested. These methods may destroy nutrients or add unnecessary byproduct to the chlorella supplement.

Sun Chlorella uses a processing method called the DYNO-Mill process which pulverizes chlorella’s indigestible cell wall— no heat or chemicals required. Pulverization allows chlorella’s valuable nutrients to become more digestible, which means you experience the health benefits of chlorella in the quickest way possible.

By adding Sun Chlorella to your diet each day, in addition to a balanced diet, you’ll be providing your body with a form of vitamin B12 it can readily use. 


from our premium chlorella products


Author: Brandi Black, RHN

Brandi Black is a Registered Holistic Nutritionist from Vancouver, B.C. Experiencing her own health challenges at a young age led her to become passionate about educating on the healing properties of food, and how to achieve hormone balance, clear skin and sustainable weight loss naturally. In her spare time you'll find Brandi writing in her blog and hanging out with her teacup chihuahua, Coconut.