This question is about Running
Runners should not take iron pills unless they are diagnosed with an iron deficiency. This can impair muscle function and athletic performance, resulting in negative symptoms such as lethargy, fatigue, impaired responses to training, and poor performance [ 1
Suboptimal iron status often occurs from low iron intake from heme rich foods (such as beef, poultry, fortified foods, or legumes). Rapid growth, high altitude blood loss, menstruation, foot-strike hemolysis, blood donation, or injury can also negatively influence iron status [ 1
1]. Unmonitored iron supplementation is not advised and may cause gastrointestinal issues, like constipation. Moreover, too much iron in the blood can be toxic and lead to negative health effects.
Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528. https://doi.org/10.1016/j.jand.2015.12.006