Which vitamin is crucial for energy metabolism as a coenzyme?

Riboflavin, also known as vitamin B2, plays a vital role in energy metabolism as a coenzyme. It is involved in the metabolic processes that convert carbohydrates, fats, and proteins into energy. In its active forms, riboflavin contributes to the formation of coenzymes such as flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are critical for various enzymatic reactions in the energy production pathways. These coenzymes help facilitate reactions in the Krebs cycle and the electron transport chain, which are essential for generating ATP, the energy currency of the cell.

In contrast, while vitamin C and vitamin K are important for other physiological functions—vitamin C is mainly known for its role in immune function and collagen synthesis, and vitamin K is crucial for blood coagulation—neither is directly involved in energy metabolic processes as a coenzyme. Calcium, though important for numerous biological functions such as muscle contraction and nerve transmission, does not act as a vitamin and does not directly participate as a coenzyme in energy metabolism. Thus, riboflavin's specific role in providing essential coenzymes for energy production solidifies its importance in energy metabolism.