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

By Brandi Black, RHN

    Active and inactive vitamin B12 are found in different plant and animal sources. Learn about their differences and how these differences affect vitamin absorption levels.

    If you often feel drained and exhausted, get dizzy spells, or suffer from anxiety, heart palpitations and nervousness, you may be low in vitamin B12. If you frequently experience digestive symptoms such as chronic gas and bloating, have pins and needles sensations in your legs, or feel short of breath, a vitamin B12 deficiency could be an underlying cause of those symptoms, too. 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 as the root cause of mood disorders, anxiety and depression (1) (2). Low levels of B12 are also present in some cases of chronic fatigue syndrome (3). 

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, or vitamin B9, to form red blood cells and synthesize DNA (4). 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(
5). When the myelin sheath begins to disintegrate, serious conditions such as schizophrenia can result (6).

Other Symptoms of B12 Deficiency May Include: 

  • Nerve problems
  • Neurological disorders
  • Pale skin
  • Loss of appetite
  • Vision loss or blurred vision
  • Loss of coordination or difficulty walking
  • Numbness and cramping in arms and legs
  • Behavioral changes
  • Depression and mood swings

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 in sufficient amounts to efficiently absorb B12 (7). 

But what we thought we originally knew about vitamin B12 deficiency may not be true. Research suggests nearly 40% of Americans between the ages of 26 and 83 have low vitamin B12 levels— and many who are affected may be completely unaware they may be borderlining on deficiency, and at risk of harming their natural wellness (8)

One reason this occurs is because serum lab tests often show normal B12 levels, when in fact, their levels are low enough to cause symptoms. This can happen because 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 normal test results based on where vitamin B12 is being stored in their body— which can raise serum B12 levels— even though they’re truly deficient. 

At present time, the most accurate method of testing for vitamin B12 deficiency is said to be the methylmalonic acid test (9). 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 test which is said to be less impacted by genetic factors or pregnancy, but is still being tested for accuracy (10). 

Aside from B12 testing methods, another reason many of us may not realize we’re deficient is because we’re eating foods that contain a form of vitamin B12 that’s not good for 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 nutrient 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 is found in plant foods, such as seaweed, spirulina and nutritional yeast. This form of B12 has been shown to be poorly absorbed in the small intestine, which is why B12 deficiency is a concern for those who avoid animal foods (11).

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

You see, inactive B12 has been called “useless” by some researchers, who’ve found that the inactive form of B12 may actually interfere with the body’s ability to use active B12 at all. 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 too many foods that contain inactive B12 (12). 

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

As you can see from the graph above,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 can outweigh the negative effects of it’s 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 co-enzymes, 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)
  • Sardines
  • Mackerel
  • Salmon
  • Milk
  • Shellfish
  • Tuna
  • Raw Milk
  • Cottage Cheese

As you can see, the foods that contain active B12 are all 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.      Now, if you follow a vegan or vegetarian diet, you’re likely wondering “well, how am I expected to get enough active B12 then?” Luckily, there’s one plant food that’s been proven to contain a highly absorbable form of active B12, and has been shown to significantly 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 has been studied as 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— after the results were extremely promising.

This study’s participants were given whole food 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. 

 Now, it should be mentioned….

Absorption and bioavailability are the most important factors when taking whole food supplements— especially chlorella.      The reason why Sun Chlorella was able to raise B12 levels so significantly 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.

Many chlorella processing methods use high temperatures and chemicals to break open chlorella’s tough cell wall, which is indigestible by the human body. These methods have the ability to destroy delicate nutrients, or contaminate 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 up to 90% more digestible, which means you experience the health benefits of chlorella in the quickest—and healthiest—way possible.

By adding Sun Chlorella to your diet each day (in addition to high quality animal products, if you include them), you’ll be providing your body with a form of vitamin B12 it can readily use, in addition to several of the other antioxidant vitamins and phytonutrients needed for optimal health.  




from our premium chlorella products