Vitamin B12 is essential for DNA synthesis and digestion, according to Mayo Clinic. This vitamin also helps fight eczema and lowers the risk for heart disease and cancer, reports Cathy Wong, N.D., for About.com.
Additionally, vitamin B12 helps regulate the metabolism, form red blood cells and maintain the central nervous system. The brain also requires this vitamin for proper functioning and development, adds Wong. It is also noted that there is not enough scientific evidence to support the claims that doses of vitamin B12 beyond the recommended daily requirement treat certain conditions, as of 2015. Despite this fact, people use vitamin B12 for the treatment or prevention of conditions such as allergies, Alzheimer's disease, asthma, back pain and depression. It is also used for osteoporosis, male infertility and diabetes.
Symptoms of a vitamin B12 deficiency include weakness, loss of balance, anemia and numbness or tingling in the arms and legs, according to Wong. Foods that are rich in this vitamin include fortified cereals, plain yogurt, milk, eggs and tuna. Side effects associated with taking B12 include diarrhea, blood clots, itching and severe allergic reactions. It is also advised to not take B12 in combination with the antibiotic chloramphenicol as it may create dangerous side effects.