When people ask about injecting something “into fat,” they are typically referring to subcutaneous injections. The subcutaneous tissue, also called the hypodermis, is the layer of fat and connective tissue beneath the skin and above the muscle layer.
Subcutaneous injections are a common route of administration for drugs like insulin or growth hormone and vaccines like MMR or chickenpox. The needle is inserted into the fatty layer below the skin, allowing for slow, sustained absorption of the substance.
Now, let’s discuss injecting B12 into fat.
What Happens If You Inject B12 Into Fat?
Whether given intramuscular (IM) or subcutaneous (SC), the goal of the B12 shots is to bypass the digestive system in patients who have difficulty absorbing B12 from the stomach. Both IM and SC can do the job, and have a long, established history of effective B12 delivery. However, for our injectable B12 we actually prefer subcutaneous over intramuscular, especially when frequent, daily dosing is needed. Here’s why:
Less Painful
For most people, SC is much less painful than IM, and it’s simply easier to stick to your B12 injection schedule when the shots aren’t painful. With frequent shots, rotating among multiple SC sites is easier and less painful than using IM sites.
Lower Risk of Injuries
Because of the depth of injection and anatomical location, subcutaneous injections carry a lower risk of hitting a large blood vessel, nerve, or bone compared to deeper IM injections. This is why some medications are purposely administered SC.
For example, an IM injection in the deltoid (the shoulder) that’s too low might risk hitting the radial nerve or the radial artery. Similarly, IM injections in the gluteal region (the buttocks) can risk damaging the sciatic nerve if not properly located.
Slower Absorption Rate
In subcutaneous delivery, it can take longer for the body to absorb and disperse the injected substance, because fat tissue has fewer blood vessels than muscles. This slower absorption can provide a more sustained release of B12, which is good, because we want a steady level of the vitamin in the bloodstream around the clock.
Remember, B12 is water-soluble. While the body does store some excess amounts in the liver, it excretes the rest in the urine. When injecting, doses are high, and there’s a lot of excess. A rapid influx of B12 might result in a greater portion being excreted, whereas a slower release could be more efficient. However, it’s hard to predict exactly how much is being absorbed. Even if a substance is released slowly, there’s still a limit. If the rate of release exceeds the rate of absorption, then the excess will still be excreted.
In Summary
When you receive a B12 shot, the body uses what it needs, stores a certain amount, and discards the excess in the urine. Often, B12 shots have a significant excess.
What happens if you inject B12 into fat, rather than into muscle?
Injecting B12 into fat has three benefits. First, this tissue has fewer blood vessels than muscle, leading to a potentially slower absorption rate for the B12, which may lead to lower amounts of B12 being excreted. Second, there’s a lower chance to hit a nerve, bone, or major blood vessels. Third, injecting into fat is less painful than into muscle.
For all these reasons, we much prefer the SC delivery over IM.
All the best.