Vitamin B12 is one of the most important essential vitamins for health and is an important coenzyme that is required by every cell in your body. Vitamin B12 is needed for red blood cell formation and DNA production, and supplementation may help with anemia, fatigue, low energy, immunity, detoxification, nerve problems, pain, mental health, insomnia, chronic illnesses, and more. Since it’s not made in the body, it has to come from an external source via diet and/or supplementation.

Vitamin B12 plays a crucial role in numerous cellular processes, most notably in the formation of new blood cells and the maintenance of neurological health. On a cellular level, B12 serves as an essential cofactor for two key enzymatic reactions involving methionine synthase and methylmalonyl-CoA mutase.

Methionine synthase facilitates the conversion of homocysteine into methionine, which is vital for producing various molecules, including phospholipids and neurotransmitters, as well as for regulating gene expression. A deficiency in B12 can lead to megaloblastic anemia. Meanwhile, methylmalonyl-CoA mutase is crucial for breaking down odd-chain fatty acids and branched-chain amino acids. A shortage of B12 results in the accumulation of methylmalonyl-CoA, which can cause the neurological issues associated with vitamin B12 deficiency.

The time it takes to feel less tired after a B12 injection can vary. Some people report feeling more energetic within a few days, while others might not notice improvements for several weeks, depending on the level of deficiency.

Effects from a B12 injection can last several weeks to months, depending on your absorption rate, metabolism, and severity of B12 deficiency.