HMS, BM EQ-Bank 77

Overview Statement

• Iron deficiency affects endurance athletes through both the endocrine and digestive systems.
• Key components include hormone production, iron absorption and oxygen transport to working muscles.

Endocrine System Effects

• The thyroid gland needs iron to produce thyroid hormones (T3 and T4).
• Low iron reduces thyroid hormone output, slowing metabolic rate and energy production.
• When oxygen delivery falls, the kidneys release erythropoietin (EPO) to stimulate red blood cell production.
• Without enough iron, bone marrow cannot build haemoglobin, so this hormonal signal fails to restore oxygen-carrying capacity.
• These relationships show that hormonal control of endurance capacity depends on adequate iron.

Digestive System Effects

• Iron is absorbed mainly in the duodenum, the first section of the small intestine.
• When iron stores are low, the small intestine increases the proportion of dietary iron it absorbs.
• However, hard endurance sessions raise hepcidin, a hormone from the liver that reduces iron absorption for several hours afterwards.
• Blood diverted away from the gut during long sessions further limits absorption around training.
• This reveals how training itself can limit the digestive system’s ability to correct a deficiency.

Implications and Synthesis

• The systems interact: the endocrine response to training limits digestive iron uptake, while low iron weakens endocrine control of metabolism and red blood cell production.
• Reduced haemoglobin lowers oxygen delivery to muscles, causing earlier fatigue and reduced aerobic capacity.
• Therefore, athletes should plan iron-rich meals around their training and pair them with vitamin C to improve absorption.
• The significance is that correcting iron deficiency requires managing both diet and training load.