Magnesium is a chemical element with the symbol Mg and atomic number 12.

It is a cofactor in more than 300 enzyme systems that regulate diverse biochemical reactions in the body, including protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation. Magnesium is required for energy production, oxidative phosphorylation, and glycolysis.

Source: 

https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/