Is It Dangerous to Have a High Level of Vitamin B12?

Your body needs Vitamin B12 for nerve tissue health, brain function and the formation of red blood cells. Because the vitamin is water soluble, any excess is excreted with your urine. For this reason, it's unlikely you could get too much vitamin B12 from food alone, but you could experience side effects from taking too many supplements. If a B12 blood test indicates your levels are excessive, it may be the sign of a disease.

The recommended daily allowance (RDA) for vitamin B12 is 2.4 micrograms for both men and women 14 years of age or older. The RDA for children is dependent on age, and pregnant and breastfeeding women need amounts above the B12 normal range, according to the National Institutes of Health. While mega-doses of vitamin B12 of 2,000 micrograms or under are considered safe in treating B12 deficiency, there is no estimated tolerable upper intake level for vitamin B12, says Healthline.

Read More: Symptoms of Low B12

Healthline advises that side effects from taking too much supplemental B12 may be mild to severe. Symptoms of high B12 might include narrowing of blood vessels, high blood pressure, dizziness, headache, cold symptoms, anxiety, itchy or burning skin with red discoloration, joint and muscle pain, edema, facial flushing, urine discoloration or gout flare-up.

Vitamin B12 can also cause very rare but serious allergic reactions. Symptoms may be swelling of the face, tongue and throat, and difficulty swallowing and breathing. If this occurs after you take vitamin B12, call 911 or your local emergency contact immediately.

Read More: Vitamin B12 Benefits & Side Effects

High levels of vitamin B12 may lead to skin conditions such as outbreaks of acne and rosacea, which cause redness and pus-filled lesions on the face. Too much vitamin B12 activates specific bacteria that can lead to acne-promoting inflammation. A study published in the journal Cutaneous and Ocular Toxicology investigated the injection of B12 in a female patient to determine the relationship between the vitamin and acne. The result was a drug-induced acne outbreak suggesting that vitamin B12 affects how genes behave in the facial bacteria of some people.

Although folate is important for women during pregnancy, excess vitamin B12 intake could be associated with a greater risk of autism in their infants. A study published in Paediatric and Perinatal Epidemiology examined the effect of high vitamin B12 levels during pregnancy and at birth in relation to early brain development in infants. Findings were that women who had extremely high levels of B12 had 2.5 times increased risk of their children developing autism, as compared with mothers who had normal levels of vitamin B12 — though, as the researchers stress, that doesn't necessarily mean B12 causes autism. In addition, because breast milk contains vitamin B12, supplementation isn't recommended for mothers who are breastfeeding, warns Everyday Health.

Alcoholism and genetic factors can cause elevated B12 levels, but an excess is more often associated with an underlying illness. High levels can be associated with diseases of the blood, such as leukemia; cancerous and other tumors; chronic liver disease; intestinal disease; blood disorders; autoimmune diseases with chronic inflammations; and hepatitis that causes vitamin B12 to accumulate in the liver, according to B12-Vitamin.org.

A study published in QJM: An International Journal of Medicine in 2013, underscored the importance of evaluating blood levels of vitamin B12 as an early marker in diagnosing disease.

If you suspect you have a high level of vitamin B12, get a B12 blood test to rule out serious diseases. Early diagnosis is vital.

Read More: The Best Way to Take Vitamin B12 Supplements