What deficiency is primarily associated with fatigue and poor athletic performance?

Iron deficiency is primarily associated with fatigue and poor athletic performance because iron plays a crucial role in the formation of hemoglobin, which is responsible for transporting oxygen in the blood. When an individual has insufficient iron, this can lead to a condition known as iron deficiency anemia, characterized by decreased hemoglobin levels. As a result, the body’s ability to deliver adequate oxygen to muscles and tissues during exercise is compromised. This inadequate oxygenation can lead to feelings of fatigue, decreased endurance, and overall decreased athletic performance.

While vitamin D, calcium, and protein deficiencies can also impact athletic performance and energy levels, their primary effects differ. Vitamin D is mainly involved in bone health and immune function; calcium is essential for muscle contraction and bone health; and protein is vital for muscle repair and building. However, none of these deficiencies directly contribute to the acute fatigue seen with iron deficiency, making iron the most critical nutrient related to the specified symptoms when it comes to athletic performance.