How Long Does B12 Take to Work? Understanding the Timeline and Effects

Gone are the days where vitamin B12 was overlooked as an essential nutrient . An essential vitamin — yes — but it often played second fiddle to vitamin C, D and Omega-3.

Well not anymore.

B12, dare we say it, has become almost… fashionable.

Madonna (allegedly) swears by it. She prefers her B12 in the form of an IV drip. It helps boost energy levels, supports brain health and possibly even promotes a faster metabolism.

While the metabolic evidence is limited to studies on rats,(1) what we do know is that B12 plays a major role in red blood cell production and formation, anemia prevention and healthy nervous system function. Getting enough is crucial. (8)

Long-term vitamin B12 deficiency can cause permanent nerve damage and neurological symptoms. (9, 10)

When it comes to B12 supplements, if an IV drip feels a little invasive, the good news is you can get the same benefits in the form of shots (intramuscular injections), or oral capsules.

But which one works fastest?

How long after taking B12 can we expect to see an improvement? How long does b12 take to work?

Let’s take a look at all things B12.

Key Takeaways

• Vitamin B12 plays a major role in red blood cell health and nervous system function.
• For B12 to be absorbed, it requires a protein called intrinsic factor (IF).
• A B12 deficiency can happen due to age, low absorption, low IF levels, or diet.
• B12 deficiency may show itself as feeling fatigued, constipated, depressed or even dizzy.
• The time it takes for B12 to work will depend on the form, how you take it, the dosage, and your current B12 status.
• B12 injection shots can usually be felt within 24 hours (and a change should show in blood tests after a month or two)
• A high dose of B12 oral supplementation takes the same time as an injection: roughly 24 hours to feel an improvement and then up to 2 months to show in blood markers.
• If you are deficient in B12, a course of injections or high dose oral supplementation may be advised.
• If you’re looking at preventative and maintenance measures, Performance Lab® NutriGenesis® Multi contains a precisely dosed optimal form of B12 along with 23 other high quality bioidentical nutrients.

Why Vitamin B12 is Important

Vitamin B12, or cobalamin, is a water-soluble vitamin that plays an important role in overall health and well-being. While its best-known role is in erythropoiesis (red blood cell formation), it’s also involved in:

• DNA synthesis

• Regeneration of bone marrow, GI lining, and respiratory tract lining

• Nervous system development and maintenance (11)

• Prevention of anemia

Although a B12 deficiency isn’t as common as vitamin D or even folate, it still happens.

It’s estimated that up to 13% of people over 60 have low levels of vitamin B12(2). But those in younger age brackets aren't necessarily in the clear. Natural sources rich in B12 tend to be derived from animal foods, so anyone following a vegan or vegetarian diet may need to supplement.

Underlying health conditions can also lead to low B12 levels. Digestive issues such as Crohn's or celiac disease can lead to impaired absorption of nutrients in the gut which may result in the need for B12 supplementation. (12)

But here’s the thing with B12—its absorption isn’t like most other vitamins.

In order for B12 to be absorbed from the gut, it requires a specific protein called intrinsic factor (IF).

B12 and Intrinsic Factor

Intrinsic factor is a protein secreted by the cells of the stomach lining. When B12 comes into our body, it's attached to proteins in the food we eat. When it hits the stomach acid, the B12 separates from the protein so it can be absorbed. Intrinsic factor binds to the separated B12 and carries it to the intestines, where it is absorbed by our body. (13)

As a result, low levels of IF can interfere with the ability to absorb vitamin B12 and lead to a deficiency. Even if dietary intake is sufficient.

Additionally, the body needs sufficient stomach acid for the digestion process to absorb vitamin B12 effectively.

Another key role of B12, along with folic acid, is helping to turn homocysteine into methionine. When converted, methionine is activated into a substance called S‐adenosyl‐methionine, which plays a vital role in our nervous system and blood health (26).

Without enough vitamin B12, homocysteine can build up. Which can be harmful. High blood levels of homocysteine pose a risk for vascular and cognitive health.

Find the best time to take B12 supplements here.

Food Sources of Vitamin B12

Eating foods high in vitamin B12 is important to prevent deficiency and stay healthy. B12 is naturally present in animal based foods such as:

• Chicken and lean red meat

• Fish and seafood such as oysters, clams, salmon, tuna and catfish

• Dairy products such as milk, cheese, yoghurt, plus vegan milk substitutes that are fortified

• Eggs

• Plus, fortified breakfast cereals. (15)

Studies show us that dairy is a better source of B12 than fish, poultry, and meat. That's because the bioavailability of vitamin B12 from dairy - how much of the vitamin is available for your body to use after consuming it - appears to be three times higher. (25)

Interestingly, the bioavailability of vitamin B12 in dietary supplements has been found to be around 50% higher than from food sources. (24)

As you can see, anyone following a strict vegan diet may struggle to obtain adequate levels of vitamin B12 in their daily diet. Vegetarians may also be at higher risk of a potential deficiency. (16)

How Much Vitamin B12 Do You Need?

Experts recommend taking 2.4 micrograms of vitamin B-12 each day. There is no identified upper limit for B12 as it's a water-soluble nutrient, meaning any excess is removed in urine.

Higher doses of vitamin B12 may be used to treat a clinically recognised deficiency. (17)

Vitamin B12 and Older Adults

It's worth making a special note here about older adults and B12. As we age, our stomachs produce less hydrochloric acid or stomach acid, which is needed to absorb B12. As such, we may struggle to absorb the vitamin B12 from food.

That's why the Office of Dietary Supplements states that people over 50 should gain most of their B12 from dietary supplements or fortified foods. The B12 found in supplements typically doesn't need stomach acid to be absorbed. (18)

Potential Causes of a B12 Vitamin Deficiency

While a vitamin deficiency, including B12 deficiency, may not be common in younger people, if you’re not absorbing what you’re eating, or you’re not consuming enough—it could happen.

In older people, a B12 deficiency usually happens as a result of insufficient levels of either stomach acid or intrinsic factor that limit absorption.

Low B12 can be caused by:

1. Diet: B12 is found in high concentration in animal products like meat, eggs, and dairy. For people following a plant-based diet that choose to exclude animal products, it can be difficult to get enough B12. However, certain foods are fortified with vitamin B12.

2. Pernicious anemia: This is a condition that develops when the body’s immune system attacks the parietal cells in the stomach that produce intrinsic factor. As a result, there’s not enough IF to absorb B12. (19)

3. Gastric surgeries: If a portion of your stomach has been removed, the body can’t produce enough IF, and the amount of space for B12 to be absorbed is also reduced. (20)

4. Intestinal problems: Because B12 is absorbed in the intestines, any disease that impairs intestinal function can interfere with B12 absorption. Conditions like celiac or Crohn's disease can impair B12 absorption.

A blood test is used to diagnose vitamin B12 deficiency.

Common Symptoms of a Vitamin B12 Deficiency

If you think you may be low, watch out for these symptoms:

• Feeling tired, fatigue and weakness
• Loss of appetite
• Constipation
• Weight loss
• Megaloblastic anemia
• Numbness and tingling
• Poor balance or coordination
• Confusion
• Memory loss
• Depression (21)
• Soreness of mouth and/or tongue (22)

Be aware that many symptoms of B12 deficiency overlap with symptoms of other health conditions, so it's important to see your doctor for a definitive diagnosis. People deficient in vitamin B12 may only experience some of these symptoms or a few in combination. (23)

How Long Does It Take Vitamin B12 To Work?

The length of time before you see the effects of vitamin B12 and symptoms subside, is going to depend on a few factors:

• B12 form
• Administration root
• Dosage
• Current vitamin B12 status

Vitamin B12 is crucial for the production of blood cells, particularly red blood cells.

Most people having B12 injections (intramuscular) will see an improvement in the first 24 hours, but the hematological response, including the quick production of new red blood cells, may take several days to months for a full response. (3)

Health professionals recommend a full blood count and reticulocyte count 7-10 days after starting treatment, and eight weeks to confirm normal blood levels. Monitoring the red blood cell count is essential to getting the right treatment.

If homocysteine or methylmalonic acid levels are abnormal, they should normalize during the first week of treatment. However, if there are neurological symptoms that have arisen due to B12 deficiency, they could take up to three months to improve, with mild improvements occurring in the first six weeks. (4)

If you’re taking B12 orally, sublingual B12 is effective because it bypasses absorption in the stomach, meaning you don’t need sufficient levels of intrinsic factor to absorb it. Oral supplements and oral vitamin B12 are also effective methods of supplementation.

There are studies to confirm that sublingual B12 supplementation is equally, if not more effective than intramuscular administration for correcting a B12 deficiency. (5, 6).

Which Works Faster, B12 Injections or Oral Supplements?

B12 injections tend to be reserved for those who are deficient. But as mentioned, there's evidence to show that high oral doses of vitamin B12 can be just as effective at treating a deficiency.

A 2005 study concluded that oral vitamin B12 and intramuscular (IM) vitamin B12 have similar effects in terms of normalizing serum vitamin B12 levels.(7) The treatment and maintenance of a B12 deficiency largely depends on what has caused it.

If an injection is deemed necessary, you may receive one three times a week, for two weeks. The maintenance dose will then depend on whether your deficiency is related to diet or not.

If it's not, you may only need an injection every 2-3 months for life. Or, a large daily oral dose.

If it is related to diet, you can get an injection every six months, or manage it through a daily oral supplement.

Depending on your B12 levels, you may want to take an all-inclusive multivitamin that gives you your daily dose of B12 alongside other important vitamins and minerals, or opt for a standalone vitamin B-complex supplement.

Best Multivitamin with Vitamin B12

Performance Lab® NutriGenesis® Multi needs to be in your supplement stack if you're looking to bridge a B12 gap in your diet, especially if you consume fewer fortified foods .

It’s an ultramodern multivitamin supplying 100% DV of 24+ essential vitamins and minerals, all bioengineered with cofactors to boost absorption and bioactivities. If offers 10mcg of vitamin B12.

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Final Thoughts

If injections aren't your thing, but you think you may be at risk of a B12 deficiency, taking a supplement is a good place to start.

If you suspect you have a deficiency, it’s best to be tested and advised by a medical professional.

If you know your levels are low, B12 supplements are a great start, but you're going to be playing catch-up, so don’t expect things to be back to normal immediately.

Because levels are often quite low before a deficiency is recognized, it can take some time for serum concentrations to even out and symptoms to subside.