Vitamin B12 is an essential nutrient that plays many crucial roles in the body. It helps make DNA and red blood cells, keeps the nervous system functioning properly, and more. Low levels of B12 can cause fatigue, memory problems, and neurological issues. So it’s important to maintain adequate B12 status. But how long does it take to increase B12 levels if they are low? Here is a detailed look at the process.
How is B12 Absorbed and Processed in the Body?
First, it helps to understand how B12 is absorbed and used in the body.
B12 is a water-soluble vitamin found naturally in animal foods like meat, fish, eggs and dairy. It can also be taken as a supplement.
When you consume B12, it travels down to the stomach where stomach acid helps release it from food. Then it moves on to the small intestine. Here, B12 must combine with a protein made by the stomach called intrinsic factor so it can be absorbed into the bloodstream.
The B12-intrinsic factor complex is absorbed mainly in the ileum portion of the small intestine. It then travels to the liver where it is stored. The liver only holds about 2-5 mg of B12 at a time.
From the liver, B12 is released into the bloodstream for delivery to tissues and organs. It binds to another protein called transcobalamin II. This protects the B12 from being filtered out by the kidneys.
B12 is used by cells throughout the body. Excess is excreted in urine.
Normal B12 Levels
B12 levels can be measured via blood tests. Different laboratories may have slightly different reference ranges but normal blood levels generally fall into these ranges:
– 200-900 pg/mL (picograms per milliliter)
– 148-716 pmol/L (picomoles per liter)
Levels below 200 pg/mL are considered low. The most severe deficiency occurs at levels below 150 pg/mL.
How Long Does It Take to Correct B12 Deficiency?
If you have been diagnosed with a B12 deficiency, raising your levels back to normal may take weeks or months depending on the severity.
Here is a look at how long it takes with different administration methods:
Oral B12 Supplements
Taking B12 supplements orally is an inexpensive and straightforward method. But only about 1.2% of oral B12 gets absorbed. The rest is not utilized by the body.
So it can take 1-2 months for oral supplementation to resolve a deficiency:
– At 500-1000 mcg doses per day, it takes 1-2 months to correct deficiency symptoms
– To replenish body stores fully, even higher doses of 2000-3000 mcg daily are recommended for 1-2 months
With oral tablets, it may take longer at lower doses. Up to 6 months for full repletion.
Sublingual Tablets
Sublingual tablets are designed to be dissolved under the tongue. This allows the B12 to be absorbed directly into the bloodstream through the tissue there.
Sublingual administration is more effective than regular tablets. It bypasses the gut absorption issues that limit regular tablets.
With sublingual forms, deficiency can be resolved within 1-3 weeks. To replenish body stores fully it may take a longer course of 1-2 months.
Intramuscular Injections
Getting B12 injections allows the vitamin to bypass the digestive absorption process altogether. B12 goes straight into the bloodstream.
This makes injection the fastest way to raise B12 levels.
With intramuscular injection, a deficiency can often be reversed in just 4-7 days.
A schedule of injections is usually given until levels normalize. Then maintenance injections may be administered 1-4 times per year to keep levels up.
High-Dose Oral or Sublingual
Taking very high dose B12 orally or sublingually can also help correct deficiency quickly. Doses of 1000-5000 mcg daily are used.
At these megadoses, enough B12 is absorbed to resolve symptoms within 1-2 weeks typically.
What Impacts How Long It Takes to Increase B12 Levels?
A few key factors impact how long it takes to replenish B12 in the body:
1. Severity of Deficiency
The more severely deficient the body is, the longer it will take to recover levels.
Mild deficiencies may resolve within 4-8 weeks. But for severe deficiency where levels are extremely low it can take 3-6 months.
This is because the body must first rebuild depleted stores before blood levels begin to rise.
2. Cause of Deficiency
Why someone is deficient also plays a role.
With dietary deficiency from inadequate intake, oral supplementation is usually sufficient to correct levels.
But if the cause is a medical condition that reduces absorption – like pernicious anemia, celiac disease, Crohn’s disease, etc. – then oral forms may not be adequate. Injections or high dose oral/sublingual would work better.
3. Age
Older adults tend to have reduced ability to absorb B12 from foods and supplements.
So they may need longer treatment or higher doses to resolve deficiency.
4. Other Nutrient Levels
Having deficiencies in other nutrients – like iron, vitamin C, folate, calcium – can impair the body’s ability to utilize B12.
Correcting deficiencies in these nutrients may help boost B12 repletion.
5. Medications
Certain medications can negatively interact with B12 absorption and metabolism. These include proton-pump inhibitors, histamine H2 blockers, metformin and others.
If medication use is interfering with B12, it may take longer to correct deficiency. Discuss alternatives with your doctor.
Signs That B12 Levels Are Improving
It will take a period of weeks or months before follow-up blood tests confirm that B12 levels have normalized.
But often, symptom improvements provide an early indication that supplementation is working.
Here are some positive signs that B12 status is increasing in the body:
– Energy and stamina improve
– Brain fog and memory issues begin to resolve
– Tingling and numbness in hands/feet starts to subside
– Balance and coordination problems get better
– Heart palpitations decrease
– Depression or anxiety begins to lift
– Sleep quality improves
Keep up with the treatment regimen. Repeat testing until levels are restored. Then have periodic testing to ensure B12 status remains optimal.
Maintaining Healthy B12 Levels Long-Term
To keep B12 levels in the healthy range long-term:
– Eat B12-rich foods like meat, seafood, eggs and dairy daily. If vegetarian/vegan, take a B12 supplement or eat foods fortified with B12.
– Treat any digestive disorders that can hinder absorption.
– If deficient due to pernicious anemia or absorption conditions, get regular B12 injections or high dose supplementation.
– Take a general B-complex vitamin to help utilize B12 best.
– Get blood levels retested at least annually, more often if at higher risk.
– Talk to your doctor about whether medications could be depleting B12.
– Limit alcohol, which can decrease B12 absorption and increase excretion losses.
The Takeaway
If your B12 levels are low, restoring them to normal ranges can take anywhere from 1 week to 6 months depending on the treatment strategy. Injections and high-dose oral/sublingual B12 work fastest, while low-dose oral tablets act most slowly. Expect more rapid improvements the more severe the deficiency. Monitor symptoms and retest levels to ensure the treatment is working and values are being maintained in range. With proper ongoing intake and testing, healthy B12 status can be sustained long-term.