Which nutrients, if low, can affect respiratory function?

The correct choice emphasizes the critical role that specific minerals such as iron, calcium, magnesium, and phosphorus play in respiratory function. Iron is essential for the formation of hemoglobin, which carries oxygen in the blood. A deficiency in iron can lead to reduced oxygen transport, thus impairing respiratory efficiency and overall oxygen delivery to tissues.

Calcium and magnesium are important for muscle function, including the diaphragm and other muscles involved in breathing. These minerals help regulate muscle contraction and relaxation, which is vital for effective respiration. A deficiency in either can lead to muscle weakness, which could hinder the body's ability to breathe properly.

Phosphorus, on the other hand, is involved in energy production at the cellular level, including the muscles responsible for respiration. Low levels of phosphorus could potentially impair muscular function and stamina, negatively impacting respiratory capability.

While the other options include nutrients that are important for overall health and other bodily functions, they do not have as direct or significant an impact on respiratory function as the combination of iron, calcium, magnesium, and phosphorus. Thus, the selected nutrients provide a more focused understanding of what influences respiration directly.