Vitamin B 12 helps to regulate the expression of genes, meaning it prevents things like cancer from happening. Most processed foods are fortified with folic acid, which masks B12 deficiency, signs of which are aggression, obsessive-compulsive behavior, sleeplessness, & tingling in the arms & legs. Don’t settle for low levels even if they are “low normal.” 200 to 1,100 picograms per milliliter is normal, but levels of under 400 increase your risk of mental health problems like dementia and depression.