The Effects of Excessive Vitamin B12

You know that there’s a long list of vitamin B12 benefits that come with getting enough of the nutrient. In fact, you need enough of it to maintain hormone balance, the health of your nerve cells, DNA synthesis and enzyme production — just to name a few. But what happens when you take too much vitamin B12? Can you suffer from a vitamin B12 overdose?

Although a vitamin B12 overdose is rare, research suggests that some groups of people are at a greater risk of adverse effects from taking an excessive amount of the nutrient. Are you at risk of a vitamin B12 overdose? If you have certain health conditions, you have to be careful of supplementing with this essential nutrient.

How Much Vitamin B12 Should You Take?

Stages of life, lifestyle changes, diet and health conditions all impact the amount of vitamin B12 you need to avoid a deficiency. The National Institutes of Health recommend the following daily dosage of vitamin B12:

• Birth to 6 months: 0.4 micrograms
• Infants 7–12 months: 0.5 micrograms
• Children 1–3 years: 0.9 micrograms
• Children 4–8 years: 1.2 micrograms
• Children 9–13 years: 1.8 micrograms
• Teens 14–18 years: 2.4 micrograms
• Adult men and women 18–50 years: 2.4 micrograms
• Adult men and women over 50 years: 25–250 micrograms
• Women who are pregnant: 2.6 micrograms
• Women who are breastfeeding: 2.8 micrograms

Adults over the age of 50 are at a greater risk of vitamin B12 deficiency because they tend to produce less stomach acid, which is needed to convert the vitamin properly. Studies show that taking 125–250 micrograms of vitamin B12 is effective for maintaining proper B12 levels for older adults. Consulting with your health care provider about the best dosage for your specific needs is recommended.

There are a few other groups that need to take more vitamin B12, usually as a supplement, to avoid deficiency. It is recommended that people who follow a vegan or vegetarian diet take one oral dose of 50–100 micrograms per day.

People with gastrointestinal issues or pernicious anemia should take a one-milligram dose of B12 daily, in either injection or oral forms. If you have any condition that impacts your ability to convert or absorb vitamin B12 properly, speak to your health care provider about the best dose for your needs.

Vitamin B12 Overdose Symptoms and Complications

Although vitamin B12 is an essential vitamin that we need to develop and function properly, what happens when we take too much of it? There isn’t a tolerable upper intake level for vitamin B12, as it’s considered a vitamin with low levels of toxicity. That means that there’s no maximum daily dose that’s known to cause adverse effects to the general population.

However, there are some groups of people that may be at a greater risk of vitamin B12 overdose. This includes people with kidney and liver disease, those with diseases related to the blood, and women who are pregnant. Studies show the consuming an excessive amount of vitamin B12 may:

• Increase the risk of cardiovascular events in people with diabetic nephropathy: A study published in JAMA sought to determine whether B vitamin therapy was able to slow the progression of diabetic nephropathy (kidney damage due to diabetes) and prevent vascular complications. Patients were given a single tablet of B vitamins containing 2.5 milligrams of folic acid, 25 milligrams of vitamin B6 and one milligram of vitamin B12 per day for 36 months or a matching placebo. Researchers found that those in the treatment group had a greater decrease in kidney function and an increase in vascular events, including heart attack and stroke.
• Have a negative impact on unborn children: A study published in Pediatric Perinatal Epidemiology found that extremely high plasma folate and vitamin B12 levels in pregnant women were associated with risk of autism spectrum disorder. Researchers conclude that this study outcome does not question the importance of getting enough of these vitamins during pregnancy but highlights concerns about the impact of a vitamin B12 overdose on offspring.

There are also negative side effects associated with vitamin B12 injections. Some of the most common complaints include:

• Headache
• Swelling
• Rash
• Facial flushing
• Itchy skin
• Dizziness
• Numbness
• Diarrhea
• Vomiting
• High blood pressure
• Cold symptoms
• Anxiety

Causes of Vitamin B12 Overdose

Vitamin B12 is a water-soluble vitamin, which means that when we ingest too much of it, the excess amounts are flushed out of the body through urine. This makes it nearly impossible to overdose on the nutrient. On top of that, we know that only a small percentage of vitamin B12 taken orally is actually absorbed.

So what may cause a vitamin B12 overdose? Research suggests that megadoses of two milligrams per day are safe for correcting a vitamin B12 deficiency. People without a deficiency should not take megadoses of B12.

Also, some people have trouble properly absorbing the nutrient because of issues involving the GI tract or lack of stomach acid. For these people, taking more and more vitamin B12 isn’t going to solve their problem. The cause of malabsorption needs to be addressed by a health care professional in these cases.

How to Prevent and Overcome Vitamin B12 Overdose

The Institute of Medicine reports that there are no adverse effects associated with excess vitamin B12 intake from food and supplements in healthy individuals. If you don’t have a vitamin B12 deficiency to begin with or you don’t first address the underlying causes of a deficiency, high doses of vitamin B12 will not work to improve your quality of life.

Researchers at Cornell University propose that vitamin B12 deficiency needs to be diagnosed correctly and reversed. However, the underlying cause of the deficiency must also be addressed in order to prevent relapse and further complications. This comes with education about how much vitamin B12 you need for your specific age, dietary choices and health.

The best way for healthy individuals to prevent a vitamin B12 overdose is to eat a well-rounded and healthy diet, incorporating foods high in B12 like organic animal meat, wild seafood, organic dairy products and eggs.

Adults over 50, vegetarians and vegans, and people with gastrointestinal issues may need to take vitamin B12 supplements to avoid deficiency. Before using megadoses of vitamin B12 to correct a deficiency, speak to your health care professional. If you experience side effects from B12 injections, ask about switching to oral doses instead.

Risks and Side Effects

• Vitamin B12 is a water-soluble vitamin. When consumed in excess amounts, it’s flushed out of the body through urine. For this reason, a vitamin B12 overdose is unlikely. In fact, studies show that for those who are deficient in the nutrient, taking up to 2,000 micrograms per day is safe.
• However, people with certain medical conditions or those receiving B12 injections may experience negative side effects or overdose symptoms.
• If you take large doses of vitamin B12 and notice adverse side effects, talk to your health care professional about the issue and ask about evaluating your ability to properly absorb the nutrient.