Vitamin B12 is a critical coenzyme involved in amino acid metabolism and protein synthesis. The recommended daily allowance (RDA) is based on sustaining optimal blood levels, assuming 50% absorption. However, 10-30% of seniors may not absorb naturally occurring B12 due to lack of intrinsic factor, so adults over 50 should meet the RDA through fortified foods. Deficiency can cause blood-related symptoms like anemia as well as neurological issues in 75-90% of cases, impacting sensations, movement, cognition, and vision. B12 is absorbed in small amounts via intrinsic factor and the stomach, and circulating levels are maintained through bile reabsorption, though deficiency develops more quickly without these mechanisms