Vitamin B12 shots are injections of vitamin B12, often prescribed for people with a vitamin B12 deficiency. Vitamin B12 plays an important role in many bodily functions, including DNA and red blood cell production, nerve function, and energy metabolism. A vitamin B12 deficiency can cause fatigue, neurological issues, and megaloblastic anemia. B12 shots provide a quick boost of vitamin B12 that can help raise B12 levels in people with a deficiency. But how long does this boost in vitamin B12 levels last after getting a shot? Here is a closer look at how B12 shots work and how long they last in the body.
How Do B12 Shots Work?
Vitamin B12 shots work by directly injecting the vitamin into the bloodstream so that it can be directly utilized by the body. Most often, vitamin B12 shots contain a form of vitamin B12 called cyanocobalamin.
When you eat foods that contain vitamin B12, like meat, fish and dairy products, the vitamin must be separated from the food source and bound to intrinsic factor in the stomach before it can be absorbed into the bloodstream. Many people have trouble properly absorbing vitamin B12 from foods due to conditions like pernicious anemia, celiac disease, Crohn’s disease, or atrophic gastritis.
B12 shots bypass this absorption process by injecting the vitamin directly into the blood. This allows people with absorption issues to get the vitamin B12 their bodies need even if they cannot absorb it properly from foods.
How Long Do the Effects of a B12 Shot Last?
So once you get a vitamin B12 shot, how long does it last? There is no definitive answer, as it depends on the individual’s vitamin B12 status and how well their body absorbs and utilizes it. However, most people can expect the effects and increased vitamin B12 levels from a shot to last 1-3 months. Here is a bit more about what influences how long B12 shots last:
Current B12 Status
If you have a severe vitamin B12 deficiency, the B12 from shots is likely to get used up more quickly as your body works to replenish stores and utilize the vitamin. In this case, you may need another shot in 1-2 months.
If your B12 levels are only slightly low or within normal range, your body does not need to utilize the B12 as quickly. In this case, a B12 shot could last 3 months or longer.
Absorption Ability
Some people have conditions that impact the body’s ability to absorb and utilize vitamin B12 properly. Even if B12 levels increase right after a shot, absorption issues may lead to faster depletion of B12 stores and the need for more frequent shots.
For example, people with pernicious anemia have an autoimmune response that blocks normal absorption of vitamin B12. Those with atrophic gastritis have low stomach acid that impairs B12 absorption. People with these conditions may only get 1-2 months benefit from B12 shots.
Dosage
The dosage of vitamin B12 in the shot will also impact how long it lasts. A typical dose is 1,000 mcg per injection, but some shots provide higher doses up to 10,000 mcg. The higher the dose, the longer the effects of the shot may last.
Of course, there is a limit to how much B12 your body can absorb and utilize at one time. Megadoses well beyond the recommended daily amount will provide minimal additional benefit.
How Often Should You Get B12 Shots?
Most doctors recommend getting B12 shots every 1-3 months to maintain adequate B12 levels. However, some people may need more or less frequent injections based on their unique situation. Here are some general B12 shot frequency guidelines:
Every Month
You may need shots every 4 weeks if:
- You have a severe B12 deficiency
- You have trouble absorbing B12
- You have a condition causing higher B12 needs, like pregnancy
Every 2-3 Months
Shots every 8-12 weeks are appropriate if:
- You have a mild B12 deficiency
- Your levels are in the low end of normal range
- You don’t absorb vitamins well from the digestive tract
Every 4-6 Months
If your B12 levels are optimal and you don’t have absorption issues, you may only need B12 shots 1-2 times per year for maintenance.
Your doctor can order bloodwork to check your B12 levels and recommend the ideal frequency for shots based on the test results and your health status.
Maximizing How Long B12 Shots Last
While B12 shots provide a boost in vitamin B12 levels, there are also steps you can take to help maximize and maintain your levels between shots:
- Take a B12 supplement. Look for a sublingual or chewable supplement that is better absorbed.
- Eat B12 rich foods like meat, eggs, dairy and fortified grains.
- Treat any conditions that impair vitamin absorption, like celiac disease.
- Ask your doctor about prescription B12 supplements or pills that contain much higher vitamin concentrations than over-the-counter products.
- Avoid excessive alcohol, which can deplete B12 stores.
- Consider probiotic supplements to support healthy gut bacteria needed for B12 absorption.
Making targeted dietary and lifestyle changes along with your B12 injections can help you maintain optimal vitamin B12 status.
The Takeaway
Vitamin B12 shots provide a direct infusion of vitamin B12 that bypasses the need for absorption from the digestive system. This allows for fast improvement in B12 levels.
On average, most people can expect the benefits and boosted B12 levels from a shot to last around 1-3 months. However, how long a B12 shot lasts really depends on the individual.
Factors like your current B12 levels, underlying medical conditions, and dosage all play a role. Work with your doctor to determine the optimal frequency for B12 shots based on your unique health status and vitamin needs.