Like all good things, too much of any vitamin or mineral can stir up trouble. Vitamin B12 is no exception and can cause side effects.
Vitamin B12 is essential for DNA production, red blood cell formation, DNA synthesis, and brain health. But if you take B12 supplements, you risk ingesting more B12 than you actually need. Here are the deets.
B12 supplements come in a variety of forms, including capsules, tablets, soft gels, gummies, and drops or sprays.
Taking these B12 supplements when you aren’t deficient may cause side effects like:
If you notice any of these side effects, stop taking B12. And call your doc if anything gets worse.
While not fully proven side effects, research has also linked the following health risks to taking high dose B12 supplements when you aren’t deficient, like:
- Skin conditions. A 2015 research review linked taking too much B12 to acne, rosacea, vitiligo, and atopic dermatitis.
- Colon cancer risk. A 2019 study found that older adults supplementing high doses of vitamin B12 were at an increased risk of colon cancer.
- More hospital time and death. A 2016 study involving hospitalized people found that the participants with high B12 levels needed longer hospital stays and had a higher chance of dying. The participants included folks with cancer, liver disease, kidney diseases, and who were older adults and critically ill.
- Failed chemo treatment. A 2019 study involving people with breast cancer found less favorable chemotherapy outcomes for the participants taking B12 supplements.
Just note, we still need more research to know these outcomes are actually linked to B12 supplements. If anything, it’s a good reminder that you should def chat with your doc about finding out if you’re deficient in B12 before you take a supplement.
If you’ve got a more serious case of vitamin B12 deficiency, your doctor may recommend B12 shots to boost those B12 levels. These injections send a high dose of vitamin B12 straight into your system, helping to counteract the effects of a deficiency.
B12 injections are generally considered safe if you’re deficient, and side effects are super rare. Still, you may experience mild side effects like diarrhea and swelling. Call your doc if these symptoms don’t go away or get worse.
You can also encounter rare, serious side effects like:
- skin rash or hives
- weak muscles or cramps
- leg pain or warm, tender pain in one leg
- dizziness and fatigue
- frequent peeing
- feeling super thirsty
- fast heart rate
- swelling of your extremities
It’s important to call your doc ASAP if you notice any of these negative effects.
Call 911 if you have an allergic reaction!
While also super duper rare, it is possible to have an allergic reaction to vitamin B12 injections.
If you have any symptoms of an allergic reaction (aka anaphylaxis), call 911 stat! These include:
- swollen face, tongue, and throat
- difficulty swallowing
- difficulty breathing
While B12 is fairly safe on its own, it doesn’t always play well with certain drugs or supplements. These meds can lower your body’s B12 levels by affecting absorption, so you might need to take a B12 supplement to keep those red blood cells in tip-top shape.
Common meds that B12 may interact with include:
- folic acid
- vitamin C
- H2 blockers
- proton pump inhibitors
- aminosalicylic acid
- gastric acid inhibitors
Talk with your doc before adding B12 to your diet if you’re currently taking any medications. To avoid any serious interactions, they may recommend specific dosage amounts or suggest taking medications and B12 supplements at different times.
B12 is a water-soluble vitamin that is absorbed in your intestines. That means any extra your body doesn’t need is flushed out of your system when you sweat or pee. (Science!)
Because of this, there’s actually no tolerable upper intake level (UL) for B12 (the max dose you can take before you experience side effects). But if you’re not deficient in B12, taking a B12 supplement is still linked to side effects.
On top of that, B12 is a unique water soluble vitamin because your body is great at storing it. An average person can have enough stored B12 to last them 3 to 5 years! That said, deficiency is rare and can only be confirmed through a lab test.
If you have any questions or concerns about what dose of B12 is best for you, talk with your doc for guidance.
First things first: If you start experiencing any side effects from taking B12 supplements, stop taking them ASAP.
Symptoms continuing to pester you or getting worse? Time to dial up your doc.
They can help figure out what’s going on (like if you’re taking doses that are too high or if another supplement is interfering with your B12 levels) and help you figure out the best course of action. This may include adjusting dosage amounts, adding more B12-rich foods to your diet, or simply skipping supplements altogether.
The National Institutes of Health shares the following recommended dietary allowances (RDAs) in micrograms (mcg) when it comes to vitamin B12:
- Teens and adults more than 14 years old: 2.4 mcg
- Pregnant women: 2.6 mcg
- Breastfeeding women: 2.8 mcg
Food is also a great source of nutritional goodness, and many people are able to fulfill all of their B12 needs through diet alone. You can get your RDA of this vital vitamin by eating B12-rich foods, like:
We know, we know: Many of these foods aren’t fit for the awesome vegans and vegetarians among us. For our more plant-based friends, there are a variety of fortified foods that can give you that B12 boost, such as certain soy products, foods containing yeast extracts, and even many bread and cereals (yums!).
Vitamin B12 is necessary for your body’s overall wellness needs. You can get most of your B12 intake from common foods, like meat, dairy, fish, or fortified foods like bread or cereal.
But if you need an extra B12 boost thanks to a deficiency, supplements or injections may help. If you aren’t deficient, you may experience side effects taking a supplement.
While rare, you may also experience not-so-fun side effects, or even a life threatening allergic reaction, from a B12 injection.
If you experience any adverse effects from your B12 supplement, stop taking it. Symptoms should go away on their own. If they don’t subside or they get worse, talk with your doc. They can see what’s up and recommend treatment.