You might be frustrated with your physician if you’re typing search terms like “how to increase my B12 levels” into search engines. You probably experienced symptoms like fatigue, brain fog, and tingling, only to be told by a physician that everything looks “fine."

The reality is that figuring out the root cause of a vitamin B12 deficiency is much more complicated than it might seem at first glance, and the standard advice some doctors give often misses the mark. Many patients report to us that they stumbled across the possibility of a Vitamin B12 deficiency themselves and had to visit multiple primary care offices before finally finding a doctor willing to order a B12 test. 

Additionally, B12 tests in isolation can fail to give the full picture as the normal range is extremely broad (often given as between 200 and 900 pg/ml). Depending on the lab, they mark you as within normal range at 305 pg/ml when a test six months ago happened to capture your B12 level at 800 pg/ml. 

If you had a change in diet, such as a sudden-onset difficulty in digesting meat, leading to you avoiding animal products, you can understand that your B12 might have been dropping since that change in your diet, which can create issues with symptoms from a functional deficiency before you hit an official deficiency.

Once you become officially deficient and this is finally accepted by your physicians, they may recommend large doses of B12 to you. For many people, your body may tolerate this approach if your body is strong enough to tolerate the roughness of US medicine. US medicine tends to try to cure things in one fell swoop rather than working gradually with the body. 

However, if you’re cautious, as you already are aware that your body has become increasingly sensitive, you can benefit from learning more about root causes for B12 deficiency, how the body absorbs and utilizes B12, why US doctors tend to recommend megadoses, and how to increase your B12 levels quickly without putting undue stress on your body. 

Our guide offers a practical look at how to get your B12 levels up fast and sustainably, so you can put deficiency behind you.

How to Increase My B12 Levels: Beyond the One-Size-Fits-All Approach

Two extremes often dominate conversations around vitamin B12 deficiency. Some physicians typically provide vague suggestions like "just eat a balanced diet" while others think you must have malabsorption and need mega-doses. Both approaches can be equally dismissive and unhelpful. The truth for each person with a vitamin B12 deficiency is more nuanced and personal. 

The recommended daily vitamin B12 intake for non-pregnant and non-lactating adults is 2.4 micrograms (mcg), but your body doesn’t absorb all the B12 it gets. The body absorbs the vitamin through a protein in the stomach with a limited capacity, termed intrinsic factor. 

Research indicates this system can potentially absorb B12 intake at a rate of 50% or higher if a well-absorbed B12 source up to a max of about 1.5 to 2.5 mcg of vitamin B12 per time slot, with the length of these windows differing from person to person. Past this natural cap, the body only absorbs B12 at about 1% which is why B12 megadoses are so high. If the RDA is 2.4 mcg, they are creating a supplement at perhaps 1,000% the RDA to bypass the natural cap and give you a higher dose of B12 absorbed (e.g., a goal of absorbing 24 mcg at 1%).  

The Malabsorption Myth and the Food Factor

There’s a pervasive idea that all people who are vitamin B12 deficient must have a malabsorption issue, such as pernicious anemia, an autoimmune condition that attacks the protein that aids B12 absorption. While malabsorption could be the cause of your B12 deficiency, it isn’t the only potential cause. Lack of B12 intake is often overlooked as a likely culprit as well as the fact that some “good” B12 sources do not necessarily promote excellent absorption in humans in general.

Take eggs, for example, a seemingly healthy source of vitamin B12. Physicians may recommend eggs as a good B12 source, but just because four eggs can equal 2 mcg does not mean that they may be the best source for you. Studies have revealed that compounds found in eggs can inhibit B12 absorption. This means you can still end up deficient or insufficient in B12 if eggs are your primary or only source of B12.

Similarly, the health status of your thyroid gland can also significantly impact your ability to absorb vitamins and minerals. A 2023 meta-analysis found that patients with thyroid disorders like hypothyroidism often have lower vitamin B12 levels than healthy individuals. An underactive thyroid can slow down your entire metabolism, including your ability to absorb nutrients. This reality is often overlooked during basic deficiency screenings. 

Why the "Take 1,000 mcg" Advice Can Be Harmful

You might have read that you need at least 1,000 mcg of supplemental B12 daily to address a deficiency, but this advice comes from protocols designed for severe malabsorption as the root cause of B12 deficiency. Supplementing that much B12 can be overkill for anyone who simply isn’t getting enough of it from their current diet or those with absorption quirks rather than severe malabsorption. 

For those people with sensitive bodies, such as those who experience severe headaches from high B12 doses, thinking that the only way to increase their B12 is to take megadoses can be misleading and harmful. It can also lead to the patients giving up. One medical website we reviewed stated that B12 could not be increased by the smaller doses present in a multivitamin. Thankfully, B12 fortification in food tends to be within the RDA. There is scant research on microdosing supplements. 

When our founder Marion Davis became B12 deficient (levels below 200 pg/mL), her severe sensitivities due to her untreated spinal CSF leak made high-dose supplements impossible. Following the common "1,000 mcg or more" rule would have been harmful.

So, she tried the opposite: a microdose of just 1.5 mcg. Within 40 hours, her blood serum level was measured and her B12 had risen by 50-80 pg/mL. This spike can be misleading if it’s read as a baseline circulating B12 level as her body still needed to utilize the B12; however, what this did indicate was roughly how much B12 could enter her bloodstream after taking a supplement and at what percentage she was absorbing B12 from the supplement.

This underscores a critical point: The dose that changes your blood level doesn’t necessarily have to be massive. For Marion, 1.5 mcg made a measurable difference and indicated to her that she could continue micro-dosing as a tolerable approach and work with her medical team towards a steady increase in her B12 levels. A 1,000 mcg dose would have been catastrophic for her system, as the methylcobalamin caused a significant burst of tachycardia for 30 minutes and the feeling of her brain shifting inside her head. 

This can possibly be explained by a sudden introduction of B12 after a deficiency, causing transient vasodilation. The body uses vasodilation and constriction already to moderate brain pressure when there is low CSF volume, compensated for per the Monro-Kellie Doctrine. This vasodilation can cause head fullness, a sensation like pressure dropping or rising, and mild disequilibrium.

This rapid reaction was likely partially due to sensitivity to the nutrient itself, due to low CSF volume equating to lower brain protection, as well as her body’s reaction to the sudden introduction of a much-needed nutrient. She was able to slowly increase micro-doses with a few days in between, with less severe reactions each time.   

A Smarter Path Forward: The Microdosing Mindset

The goal of microdosing is to work with your body’s natural absorption windows and tendencies, instead of trying to force down large doses. Too much B12 can be harmful just as too little is harmful. 

At some point, you have to ask yourself: if the body uniquely controls the absorption of this specific vitamin in a different way than other vitamins, specifically putting that cap there, is the right approach to override this? At times, yes. But not in every case. And this is why it’s important to ask questions. 

• Think "little and often:" Instead of taking one giant supplement, consider smaller amounts spread throughout the day. This mimics how you'd get B12 from food and respects the body's absorption cap.
• Choose your B12 source wisely: Understand that absorption rates vary if you're using food as your primary source. Animal proteins, like fish, meat, and dairy, are generally well-absorbed. Patients with sensitivities can explore different low-dose supplement forms, like methylcobalamin or adenosylcobalamin, instead of the synthetic form of B12, cyanocobalamin, under the guidance of a physician. Some people may absorb one form of B12 better than another or have more symptoms with one form over another. 
• Look at the big picture: Explore all potential causes of your B12 deficiency before resigning yourself to a lifetime of vitamin supplements or injections. Is your thyroid gland functioning optimally? Are you taking medications like metformin or acid blockers that can affect B12 absorption? Are you eating B12 at the right time of day? Are you eating a potentially low-absorbed form of B12 before a potentially higher-absorbed source of B12 and creating a B12 bottleneck, such as eggs one hour before aged cheese with B12-producing bacteria? These are all conversations to have with your doctor and/or dietitian.

Your Next Steps: From Confusion to Clarity

You don’t have to settle for getting dismissed or being subjected to incompatible one-size-fits-all protocols to improve your vitamin B12 levels. The most effective approach is a personalized one that considers your diet, your body’s sensitivities, how you respond to supplementation or food-based sources, and your overall health.

We’re here to help if you’re tired of guessing and ready for a strategy that respects your unique biology. MedicalOfficeMarketing.org provides patients with learning materials created in collaboration between US patients who’ve walked the walk and international clinicians from countries with a heavy emphasis on nutrition, metabolism, and continuous and collaborative learning as part of modern medicine. These materials will give you a starting point to better understand what could be happening in your body so that you can show up to visits with your medical team as an informed patient. 

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