VITAMIN B12 IN ENERGY METABOLISM AND ITS ASSOCIATION WITH BODY WEIGHT

Vitamin B12 (cobalamin) is an important water-soluble micronutrient that serves as one of the key inputs for cellular metabolism, especially DNA synthesis, methylation, and mitochondrial function. Its function spreads to fundamental energy production pathways by serving predominantly as a co-factor with two important mammalian enzymes such as methionine synthase (MTR) and methylmalonyl-CoA mutase (MMUT). The MMUT-catalyzed reaction bridges catabolism of certain amino acids and odd-chain fatty acids to the tricarboxylic acid (TCA) cycle, a cellular energy production-evolving center. The MTR reaction is essential for the methionine cycle and global methylation during nucleotide synthesis. These essential functions have led to heightened interest in the association of vitamin B12 in metabolic health and, as such, body weight control. Serum B12 levels consistently have an inverse association with body mass index (BMI), with lower reported levels reported in individuals with obesity. It remains uncertain, though, whether low levels of B12 in the body promote weight gain or if obesity-related factors lead to lower B12 levels. This review summarizes the biochemical status of vitamin B12, discuss its unique roles within energy metabolism, and review the evidence from human studies relating B12 status and body weight. We assess possible mechanisms of action like lipid metabolism, insulin resistance, or mitochondrial performance, but we emphasize that research to date is limited and B12 itself should not be regarded as an actual weight-losing agent. Grasping this nuanced interplay will be particularly important for students of the biochemistry and the medicine disciplines who wish to link micro-nutrient status with metabolic health on a systemic level.