Magnesium 400 mg Capsules - Nervous System Support. Magnesium is a mineral that is critical for energy production and metabolism, muscle contraction, nerve impulse transmission, and bone mineralization. It is a required cofactor for an estimated 300 enzymes. Among the reactions catalyzed by these enzymes are fatty acid synthesis, protein synthesis, and glucose metabolism. Magnesium status is also important for regulation of calcium balance through its effects on the parathyroid gland. Natural colour variation may occur in this product.