Through their transmission of diseases like malaria, yellow fever, and West Nile virus, mosquitoes have been responsible for more deaths than any other animal in history. Yellow fever alone killed thousands of people in the U.S.-- up to 10% of the population in some areas-- (REF: 1) and West Nile virus cases currently in nearly every state. (REF: 2) Even uninfected mosquitoes are nearly universally reviled as they irritate us with their itchy bites. So it's understandable when people reach for easy ways to repel these blood-sucking insects. Vitamin B12, also known as cobalamin or cyanocobalamin, is one such easy solution. Unfortunately, there's no evidence that it works.
Entomologists Naysay B12
The American Mosquito Control Association specifically states that Vitamin B12 does not work as a systemic repellent. (REF: 3) However, it does appear that some people are more attractive to mosquitoes than others. Entomologist Karl-Martin Vagn Jensen of Aarhus University and colleagues found that the smells of certain people, transferred to petri dishes for testing, did attract mosquitoes more than others. However, B vitamins do not appear to responsible, according to Dr. Jensen. (REF: 4) Scientific studies specifically testing Vitamin B12 as a repellent found that it had no significant repellent ability to repel mosquitoes. (REF: 5)