Which mineral is essential for oxygen transport in the body?

Iron is essential for oxygen transport in the body primarily because it is a key component of hemoglobin, the protein in red blood cells responsible for carrying oxygen from the lungs to the rest of the body's tissues. Each hemoglobin molecule can bind to four molecules of oxygen, and the presence of iron in its structure allows this binding to occur. Without adequate iron, the production of hemoglobin is compromised, which can lead to a form of anemia characterized by reduced oxygen-carrying capacity.

In the context of the other minerals listed, calcium plays roles in muscle contraction and bone health but is not involved in oxygen transport. Sodium is vital for fluid balance and nerve function, while potassium is important for muscle contractions and heart function, but neither sodium nor potassium facilitates the transport of oxygen in the bloodstream. Therefore, iron stands out as the critical mineral for this specific function.