Vitamin B12 is a water-soluble vitamin necessary for healthy nerves and red blood cells. If you don’t get enough from your diet, a doctor may recommend supplements. Here’s what to know about dosage, risks, and more.
Vitamin B12 is added to some foods, like cereal, and can be found naturally in a variety of animal-based products, including fish, meat, eggs, and poultry. How much you should get daily depends on age and overall health. Here is the recommended dietary allowance (RDA) for vitamin B12:
Age
Recommended Amount
Birth to 6 months
0.4 micrograms (mcg)
7-12 months
0.5 mcg
1-3 years
0.9 mcg
4-8 years
1.2 mcg
9-13 years
1.8 mcg
14 years and older
2.4 mcg
Pregnancy
2.6 mcg
Breastfeeding
2.8 mcg
If you’re interested in taking a vitamin B12 supplement, it’s best to discuss dosage with a medical professional. However, experts typically recommend taking between 500 mcg and 1,000 mcg of vitamin B12 per day, which is higher than the RDA because only a small percentage of the vitamin is absorbed.
Your body stores up to 2,000 times as much vitamin B12 as you eat daily. However, some people do not get enough through their diet. Others may have conditions that make it hard for the body to absorb it.
You may need B12 supplementation if you fall into one of the following categories:
- Have an autoimmune disorder (e.g., Crohn’s or celiac disease)
- Are an older adult
- Recently had weight loss surgery
- Follow a vegetarian or vegan diet
In more severe cases, you may need B12 injections to ensure your body absorbs it effectively. You may switch to oral supplements once levels become normal, but some people need injections for life.
Vitamin B12 can be used sublingually (under your tongue) and nasally, but these are not well studied and may be expensive.
Vitamin B12 deficiency symptoms can vary. Some common signs of low B12 levels include:
- Dizziness
- Fatigue
- Headaches
- Jaundice (yellow eyes and skin)
- Lower appetite
- Nausea
- Painful, smooth, red tongue
- Rapid heart rate or shortness of breath
- Tingling in hands and feet
- Weight loss
Less common symptoms include uncontrolled muscle movement, vision changes, depression, poor memory, confusion, and mouth or tongue soreness.
Vitamin B12 is generally safe. In high doses, you may develop side effects like:
- Allergic reactions
- Fever
- Itching
- Pain at injection sites for people who use intramuscular (IM) vitamins
- Rapid weight gain
- Rash
- Shortness of breath
People who use B12 injections are more prone to allergic reactions.
Cyanocobalamin—the synthetic form of vitamin B12—has an aluminum component that can worsen kidney function. People with kidney-related conditions should use methylcobalamin, the natural form.
Keep in mind that if you develop anemia due to a B12 deficiency, your complete blood count may take up to eight weeks to return to normal. More severe symptoms like memory problems, numbness, or tingling can take months to resolve.
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National Institutes of Health: Office of Dietary Supplements. Vitamin B12 – health professional fact sheet.
Wang H, Li L, Qin LL, Song Y, Vidal-Alaball J, Liu TH. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev. 2018;3(3):CD004655. doi:10.1002/14651858.CD004655.pub3
Al Amin ASM, Gupta V. Vitamin B12 (cobalamin). In: StatPearls. StatPearls Publishing; 2023.
National Heart, Lung, and Blood Institute. Vitamin B12–deficiency anemia.
Ankar A, Kumar A. Vitamin B12 deficiency. In: StatPearls. StatPearls Publishing; 2024.
Vasavada A, Patel P, Sanghavi DK. Cyanocobalamin. In: StatPearls. StatPearls Publishing; 2024.
