It is hard to say with 100% accuracy how long a vitamin B12 injection lasts in the body. It all depends on how your body reacts to vitamin B12 shots and the frequency that you inject. In other words it’s a bit different for everyone.

Many studies show that people are unable to absorb or store sufficient amounts of vitamin B12. These absorption and storage issues stem from a variety of reasons and range from serious (medical) to benign (diet). Many people use B12 injections as opposed to oral supplements, as injections are more easily and quickly absorbed by the body.

However, one reputable source, written by Larry E. Johnson, MD, PHD at the University of Arkansas for Medical Sciences, explains that when people can properly absorb and store vitamin B12, it is stored within the body from between 3 to 5 years.

Just one of the thousands of reasons the body stores vitamin B12 is because it is necessary for the development of appropriately sized red blood cells, which are essential in reducing the risk of Pernicious Anemia and other ailments that we’d all rather avoid.

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What factors can affect how long a B12 injection lasts?


Lifestyle Choices

If you regularly enjoy a beer or drink, as many of us do, your body is likely to be using more vitamin B12. This means you will benefit from taking additional B12. Doing this is also reported to help speed up hangover recovery. Drinkers rejoice!

Several studies have found that how long B12 remains in your system can depend on many things and underlying factors such as tendencies towards developing certain diseases, as well as your lifestyle choices. These can include diet, drinking, medications, drug use and so forth. We’re all naturally different, so vitamin B12 stays in our bodies for different amounts of time.

Liver Issues

Those who suffer from liver disorders are often unable to store B12. If you suffer from a liver disorder, you will most likely be prescribed and benefit from regularly taking vitamin B12 injections. 50% of the body’s storage of vitamin B12 is kept within the liver, no matter how it is administered, so if your liver is sick, in all likelihood you can suffer B12 deficiency.

Excess vitamin B12 is expelled through urine, so there is little need to feel uneasy about injecting too much B12.


How quickly is a B12 injection absorbed?

Injections bypass the need for the vitamin to be absorbed by the intestines so the body can begin using it within minutes. Vitamin B12 given through subcutaneous or intramuscular injections is rapidly absorbed and used by the body as needed. Studies show that between 50% to 98% of injected B12 is found in the urine just 48 hours after the injection is administered, meaning it may have a half-life of up to 24 hours.

During the time it is in your body, your body sends and uses it where it is needed, and if you are able to store it and there is any excess it helps tops up your liver reserves.


So, how often should I inject B12?

It’s a good idea to develop an injection routine that works well for you. This could be daily, weekly, bi-monthly or monthly. If you suffer from conditions that lead to B12 deficiencies or already have a deficiency, then you should maintain a routine until your symptoms clear up, and then follow your doctor’s specific maintenance regimen.

Your doctor can help you figure out how well your body stores B12 by taking a full blood count. Further MMA testing will provide a more complete analysis of the vitamin B12 available in your body. These results will help your doctor prescribe a proper routine that works best for your case.

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Take Away

  • From the research conducted so far, injections are absorbed within minutes and bypass any existing complications involved with oral absorption. This means B12 injections are absorbed and readily available quicker than oral supplements.
  • Professionals have suggested that the vitamin B12 from intramuscular and subcutaneous injections remains in the body for up to 48 hours, before 50% - 98% of any surplus vitamin is filtered out through urine. Most of this is filtered through the body in the first 8 hours after taking the injection.
  • Studies show that how long B12 injections last varies depending on factors such as lifestyle choices and underlying medical conditions.
  • You should always consult your doctor or a trained medical professional before using vitamin B12 injections.