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Question: Can taking too much vitamin B-12 be dangerous? The label on my B-complex states it contains 50,000% the Daily Value!
Answer: If your B-complex contains 50,000% of the Daily Value (DV), which is 6 mcg for adults, then it has 3,000 mcg of B-12. For people without a severe B-12 deficiency, this is certainly more than necessary. [Update: In 2016, the FDA lowered the Daily Value for B-12 to just 2.5 mcg for adults, but this won't be reflected on most supplement labels until 2018 or 2019.]
Taking some B-12 is advisable for people over the age of 50 (when you're less able to extract B-12 from food), as well as for those taking medications that interfere with B-12 absorption, strict vegetarians, alcohol and drug abusers, people recovering from surgery or burns, and those with bowel or pancreatic cancer.
Although vitamin B-12 is generally considered to be safe, and no "Upper Tolerable Intake Level" has been established, there are some reports of doses of 20 mcg per day or higher causing outbreaks of acne and rosacea. There is also a study which showed that a high-dose B complex supplement (with 1,000 mcg of B-12) hurt, rather than helped, people with type 1 or type 2 diabetes and advanced kidney disease, resulting in a worsening of kidney function and an increase in the risk of heart attack, stroke and death.
In women who are pregnant, excessive blood levels of vitamin B-12 have been associated with an increased risk of autism in their children.
In general, it's best to avoid excessive doses of any vitamin if it is not needed.
Get more information, including the Recommended Daily Allowance for B-12 (by age and gender), differences in the forms of B-12, potential side-effects and drug interactions, plus ConsumerLab.com's tests of popular products, in the B Vitamin Supplements Review >>
You can check the recommended intakes of other vitamins and minerals here.