Does Vitamin B12 Have Any Side Effects? Here’s What You Need to Know
Absorption
Let’s start with a quick look at how vitamin B12 is absorbed. When you take high doses of vitamin B12 orally, its absorption rate is quite low. For B12 to make it through the digestive system and into your bloodstream, it needs to bind with something called intrinsic factor. The amount of B12 that gets absorbed depends on how much intrinsic factor is available. Because of this, taking large amounts of B12 orally is unlikely to cause any problems since not all of it gets absorbed. Even when B12 is absorbed through the tissues in your mouth (sublingual absorption), the levels aren’t high enough to worry about.
Symptoms of Deficiency
There are a couple of reasons why someone might be deficient in vitamin B12. One is not eating enough foods that contain B12, like red meat, fish, or dairy products. This is a common issue for vegetarians and vegans. Another reason is having trouble digesting B12 due to low levels of intrinsic factor, which can be caused by genetic factors or physical damage to the stomach or small intestine.
Common symptoms of B12 deficiency include numbness in the hands and feet, mood swings, memory problems, dementia, poor red blood cell formation, impaired DNA function, and fatigue.
B12 Side Effects
Vitamin B12 exists naturally in three forms: methylcobalamin, adenosylcobalamin, and hydroxocobalamin. There’s also a lab-made form called cyanocobalamin, which uses cyanide for stabilization and is found in many low-quality supplements. Injections are often used for people who can’t digest and absorb B12 properly. Many vegetarians and vegans are B12 deficient because they’ve cut out natural dietary sources of the vitamin. Surprisingly, many meat-eaters are also deficient.
Some side effects have been reported from cyanocobalamin injections, including itching, acne, nausea, diarrhea, blood clots, headaches, nervousness, and dizziness. However, studies have shown that a 1 mg injection of cyanocobalamin doesn’t usually cause any significant side effects.
No Upper Limit Safety Recommendations Exist
There haven’t been any adverse or toxic reactions to vitamin B12 from dietary consumption or supplement use. The US Food and Nutrition Board hasn’t set any upper safety limits for B12 in healthy people. Although it’s always a good idea to check with your doctor before starting a new supplement routine, B12 supplementation is generally considered safe. If you’re looking for a safe, natural B12 supplement, I recommend Global Healing’s B12. It’s a vegan-safe formula that contains methylcobalamin and adenosylcobalamin, along with hydroxocobalamin for long-lasting support, providing 5,000 mcg of B12 per serving. It also includes Energized Trace Minerals for enhanced bioavailability.