Story at-a-glance Research suggests "normal" vitamin B12 levels are insufficient for optimal brain health, especially in older adults, despite being above the standard medical threshold Vitamin B12 helps your nerves work well by protecting them with a special coating, allowing brain messages to travel quickly and clearly A study of healthy older adults showed that lower B12 levels, even within the "normal" range, were linked to slower thinking and brain signals Signs of low B12 include brain fog, memory issues, tingling in hands and feet, and mood swings; these symptoms often develop gradually Rich sources of B12 include grass fed meat, eggs and dairy; supplementation is often necessary for vegans, older adults or those taking certain medications like metformin