Is Vitamin B12 Dosage 5000 mcg Safe?

By Scott Burgett | 5.9.18


The conversation of Vitamin B12 supplementation has been exploding recently due to the popularity of plant-based diets. Since this vitamin is hard to obtain strictly through plant foods, medical professionals everywhere recommend supplementing Vitamin B12 for those who follow a vegan, vegetarian, or plant-based diet. But is Vitamin B12 dosage 5000 mcg safe?

With single serving doses on supplement bottles ranging greatly, it’s confusing to know how much to take on a daily or weekly basis. Additionally, ingesting high quantities of a supplement could have negative health consequences.

This post will explore the risks, benefits, origins, dosing guidelines, and the best supplement recommendations for Vitamin B12. 


What is Vitamin B12?

Vitamin B12 is a water-soluble vitamin that plays several pivotal roles in the human body. These functions include red blood cell formation, nerve cell repair, and DNA synthesis. Each of these processes are vitally important to maintaining health throughout your life.

This fundamental vitamin actually originates from microorganisms that blanket the earth. Once upon a time when modern agriculture was unheard of, these organisms thrived in our soils and mountain streams. However, since the invention of harmful pesticides and power washing, these organisms are rarely found in our food supply anymore.

In the scientific community, Vitamin B12 is referred to as a “cobalamin.” It gets this name because it’s the only known vitamin that contains the form of the metal “cobalt” and still biologically reacts with humans, plants, and animals. Cobalt is actually what gives Vitamin B12 its natural red color.

Now that you understand the role of Vitamin B12, there are two forms of it you need to know. These two forms are the most common forms of the vitamin that are found in fortified foods and supplements.


The Two Forms of Vitamin B12 You Need to Know

Vitamin B12 is the largest and most complex vitamin we know today. In supplements, it comes in two primary forms: methylcobalamin or cyanocobalamin. These two forms differ in a couple of key areas explained below.



Methylcobalamin is the best absorbed form of supplemental B12 in the body because it is bioactive. In other words, it’s readily available to positively interact with our cells.

This form has a chemical structure that contains a methyl group (hence the name), which consists of a hydrogen and oxygen molecule. This methyl group makes it the most active form of Vitamin B12 in the body.

Methylcobalamin is also the most common form of B12 found in animal foods. That’s why omnivores do not need to supplement with B12; they get it through their food.



The only synthetic form of Vitamin B12, cyanocobalamin differs greatly than other forms because its chemical structure contains a cyanide group. This cyanide group is the same as the poisonous cyanide you’ve heard of before, but irrelevant to the body at the levels found in Vitamin B12. It is also the only form of Vitamin B12 that is created in a lab setting.

The synthetic nature of this form requires more steps in the breakdown process and could potentially cause absorption issues. Cyanocobalamin has been researched and used in supplements for years due to its proposed effectiveness. Although more recently, criticisms in the scientific community have started to surface regarding its:

  • Toxic build up in the cells
  • Bioavailability due to its complex breakdown process
  • Absorption to excretion ratio (what stays and what leaves the body)

Due to these criticisms and recent research, cyanocobalamin is now an inferior form of supplementation to methylcobalamin


How is Vitamin B12 is Processed in the Body?

The most prominent source of Vitamin B12 is found in animals products. Animals obtain the B12 in two ways: eating grass that has B12 in the soil or through supplementation in their feed. The latter being the most common practice in our world today.


Ingestion to Absorption Through Food

Since humans still eat animals, they obtain Vitamin B12 through their food. For example, when a person eats meat, the Vitamin B12 in that animal’s tissue enters the stomach. This B12 is protein-bound, meaning it attaches itself to a protein molecule for transport. Before it enters the small intestine, it has to detach in the stomach.

Once the B12 detaches from the protein in the stomach, it’s picked up by a different protein molecule called intrinsic factor (IF). IF then enters the small intestine bound to Vitamin B12 and gets separated once again into a group called corrinoids (a class of cobalamins, aka Vitamin B12). These separated corrinoids attach one more time to a different form of IF and heads to its destination in the small intestine.

Once there, the receptors in the small intestine give the corrinoids (Vitamin B12) first priority to absorb. This ensures the body gets this crucial vitamin over other nutrients that have passed through at the same time.


Ingestion to Absorption Through Supplements

The supplemental form of B12 gets absorbed much easier through supplements than food. That is because is not bound to protein like in animal tissue. In fact, the only step it takes to break down is either by chewing or by stomach acid (if swallowed whole).

It is then absorbed directly into the bloodstream and shuttled to it’s final destinations: blood cells, the brain, and DNA. This makes the supplemental form of Vitamin B12 the most reliable form we have available.


Symptoms of a Vitamin B12 Deficiency

It is non-negotiable for anyone following a vegan or plant-based diet (and in most cases a vegetarian diet) to not supplement with Vitamin B12. Symptoms of B12 deficiencies often do not show for several years, which is why it’s important to start forming the habit early. The below symptoms are some of the most common from a B12 deficiency. 

Early signs of a Vitamin B12 deficiency:

  • Unusual fatigue
  • Nausea
  • Loss of appetite
  • Diarrhea
  • Deficient digestion
  • Numbness/tingling in hands or feet
  • Loss of menstruation
  • Unusual behavior changes
  • Sore tongue

Later signs of a Vitamin B12 deficiency:

  • Blindness
  • Deafness
  • Dementia
  • Paralysis
  • Death

Note that you can still be deficient even though none of these symptoms are detectable. Getting regular blood tests will you get ahead of a potential deficiency, but regular supplementation is the best practice.


Two Alarming Case Studies of Vitamin B12 Deficiencies

A frightening case in the US made it into the Medical Journal of Nutrition in 2007. The journal article was title “Irreversible subacute sclerotic combined degeneration of the spinal cord in a vegan subject.” This case involved 57-year old man never being able to walk again because he did not supplement with Vitamin B12 on a vegan diet.

Doctors immediately started giving him B12 injections for treatment. This dramatically improved his health, however, his rotten spinal cord left irreversible damage. This left him paralyzed for the rest of his life.

Deficiencies can even happen to infants with vegan or vegetarian mothers who neglect to supplement with B12 during pregnancy. In 2014, a Chilean 12-month old, daughter of a long time vegetarian showed severe neurological issues after birth.

Similar to the man above, doctors immediately started treating her with B12 injections. Luckily in this case, the child improved significantly after several of these injections, but she continued to show signs of developmental issues as she aged.

A B12 deficiency can have potentially irreversible consequences and affect all ages. Although rare, it can happen to anyone. Use these stories as a lesson to maintain a regular supplementation schedule.


Food Sources of Vitamin B12

Vitamin B12 is found naturally in animals foods including meat, fish, poultry, eggs, and milk products. However, it’s most prevalent in the specific foods outlined below.

Best animal foods with Vitamin B12:

  • Clams
  • Beef Liver
  • Wild Rainbow Trout
  • Sockeye Salmon
  • Light Tuna Fish, canned in water

Vegan and vegetarian B12 food sources are much more scarce. Even though B12 is found in sea vegetables, it is an unreliable source due to impostor enzymes. These impostor enzymes are not active in the body and can sometimes alter blood tests to show elevated levels of Vitamin B12 in the blood stream. Therefore, the two options below are the best food sources for vegans.

Best vegan foods with Vitamin B12:

  • Nutritional Yeast
  • Vitamin B12 Fortified foods (typically in plant milks or cereals)

Nonetheless, due to the unreliable nature of food sources, supplements are still recommended as best practice for vegans and vegetarians.



How much Vitamin B12 do you need?

These recommendations were developed by the Food and Nutrition Board at the Institute of Medicine of the National Academies. They will meet the needs of 98% of healthy individuals. However, those with unique medical conditions should speak with their doctor for specific dosing protocols.

Recommended Daily Intake (RDA) for Healthy Adults:

  • 2.4 mcg per day

Additionally, pregnant females need slightly more at 2.6 mcg per day, and lactating females need 2.8 mcg per day.

Supplementation Guidelines

Most Vitamin B12 supplements start at at least 250 mcg and go as high as 5000 mcg per dose. As you can start to see, a once daily or once weekly supplement will more than satisfy the RDA.

Choose one of the two dosing guidelines for Vitamin B12:

  • 250 mcg per day OR
  • 2500 mcg per week

Typically, people choose the once per week option because most supplements are sold in higher doses. With that, you will find the best value for your dollar and can avoid supplementing with pills on a daily basis.

It’s also best to take Vitamin B12 supplements during the day since they stimulate the nervous system and can cause a caffeine-like effect in the brain. Some people report trouble sleeping if taken too late in the day. As a rule of thumb, take the supplement before 1 p.m.


So is Vitamin B12 Dosage 5000 mcg Safe?

Given the current state of research, 5000 mcg of Vitamin B12 supplementation is a safe dosing amount. Although, you do not need to consume that much.

With the RDA at only 2.4 mcg for healthy adults, taking 5000 mcg just creates expensive urine. You can safely dose at lower levels and still reach the RDA. Additionally, our bodies can store Vitamin B12 in our tissues for several years, so overloading is unnecessary. 

In other words, more is not better when dosing for Vitamin B12.

The only exception that would make sense dosing at 5000 mcg (daily or weekly) is if you are receiving treatment from a B12 deficiency. Likewise, if you have a health condition that affects absorption rates. In either of those scenarios, you would be working with a health professional to establish a proper dosing protocol.



Best Vegan Vitamin B12 Supplements

Whether you prefer chewable, liquid, or sublingual, all forms work. There is some evidence showing sublingual absorbs more efficiently into the bloodstream, but it’s not enough to shun all other forms of Vitamin B12 supplements.

One item to note is that many non-vegan ingredients can sneak into B12 supplements. While it’s always best to seek vegan-approved labels, there is not one regulated standard agency. Use the below list of ingredients to identify whether or not your supplement is vegan approved.

The most common non-vegan ingredients used in B12 supplements:

  • Lactose
  • Gelatin
  • Intrinsic Factor

Other ingredients that could be either animal or plant-based (usually the label with state the difference):

  • Magnesium Stearate
  • Stearic Acid

Due to strict false-advertising regulations, labels that claim a Vitamin B12 supplement is vegan friendly will be the case. To make your decision easy, use this vegan friendly supplement list below.

Top Five Best Selling Vegan Vitamin B12 Supplements on Amazon:


Vitamin B12 Wrap-Up

If you are a vegan or vegetarian, you must supplement with Vitamin B12. Otherwise, you run the risk of developing serious conditions later in your life such as dementia, blindness, or even death. Just like buying insurance for your vehicle, use Vitamin B12 as an insurance policy for your health.

Unless you have specific medical condition that calls for large amounts of Vitamin B12 supplementation, dosing at 5000 mcg is worthless. Our bodies can absorb an adequate amount through a methylcobalamin containing Vitamin B12 supplement at 2500 mcg on a weekly basis or 250 mcg daily. Anything more is flushing your hard-earned dollars down the toilet.


Do you supplement with Vitamin B12? If so, what dosage do you take? Share in the comments below!

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8 Comment(s)

  1. Abu
    September 11, 2018

    I was diagnosed with low white blood cells. The complete blood test checking everything including HIV came out negative. But my B12 vitamins was normal but right on the edge to be on the lower side. Since he couldn’t think of any other reason my Dr recommended B12, he said sometimes this could be the reason. He prescribed the injection but couldn’t afford it and he put me on sublingual 5000 mcg methylcobalamin instead. When I knew about this website I had already bought vegan EZ MELTS. My diet was mostly a lot of vegetables and fish occasionally chicken and very rarely beef. I am over 60 and could feel like having a little hard time remembering things but not that bad. EZ Melts is not on your recommended list but I chose it because I wanted to avoid gelatin. Thank you for your informative article.

    1. Scotty
      September 11, 2018

      Hi Abu, I am happy to hear you are working with your doctor for your low white blood cell count. All the product recommendations in this article are vegan friendly (meaning no gelatin). Feel free to order one of them the next time you need to replenish your Vitamin B12 supplement.

  2. Shinny
    September 29, 2018

    Is it dangerous to overdose on sublingual B12? What will happen?

    1. Scotty
      September 30, 2018

      Great question Fair Haven Farms. It’s highly unlikely anyone could overdose on B12 because No Tolerable Upper Intake Level (UL) has been established by the FDA. Additionally, since it’s a water soluble vitamin, any excess B12 will get excreted through the urine.

  3. Heloisa
    October 6, 2018

    Speaking of excreting b12 in the urine; does it alter the urine color? I notice urine coloration with nutritional yeast (strong yellow), but not with 5,000 mcg Methylcobalamin liquid drop (sublingual)… Hmmm, is the b12 quality different on these two, therefore excretion is somehow different?

    1. Scotty
      October 7, 2018

      Typically taking a B-complex vitamin alters the urine color (due to Vitamin B2 specifically). However there have been cases of high B12 intake changing urine color. If you feel it’s serious, I recommend speaking to your doctor about it.

  4. Angela
    October 27, 2018

    Is it best to take B12 5000 mcg every 2 weeks?

    1. Scotty
      October 29, 2018

      Great question Angela. It is recommended to take 2500mcg weekly. Even though that equates to 5000mcg bi-weekly, all of the medical recommendations I’ve come across stick to a weekly supplement.

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