TMG (trimethylglycine) is taken with NMN (nicotinamide mononucleotide) or NR (nicotinamide riboside) because it can help to increase the absorption and effectiveness of these NAD+ precursors. NAD+ is a molecule that is essential for cellular energy production and many other important functions in the body. It declines with age, which is one of the factors that contributes to aging.

TMG is a methyl donor, which means that it can donate a methyl group to other molecules. This is important for the production of NAD+, as the body needs methyl groups to convert NR and NMN into NAD+. TMG can also help to protect the mitochondria, which are the cell's powerhouses. This is important because mitochondria are damaged with age, which can contribute to aging and age-related diseases.

In addition to increasing the absorption and effectiveness of NMN and NR, TMG can also have its own anti-aging benefits. It has been shown to increase lifespan in mice, and it can also protect against age-related diseases such as Alzheimer's and Parkinson's.