The nervous system works in two parts; the sympathetic nervous system works primarily in “fight or flight” mode. The parasympathetic nervous system focusses on “rest and digest”.
So, opposites, to a point. You can’t run away whilst resting!
When exercising (or running away!) blood flow is directed to muscles – often screaming for oxygen to keep you going – and so the blood flow to the stomach lining decreases. The body requires iron to transport oxygen from the lungs throughout the body and to muscle tissue, which uses oxygen to create energy. Without adequate iron stores, athlete’s performance suffers.
Iron deficiency is a common cause of tiredness, or overtraining syndrome, particularly in endurance athletes – runners, cyclists, swimmers. Active people are susceptible to iron deficiency for a number of reasons; primarily, iron intake, increased iron loss, inadequate iron absorption. Other factors to consider include menstruation, and internal bleeding.
Iron, when eaten, is absorbed (in a state called ferrous) in the first & second section of the small intestine (duodenum and proximal jejunum).
In the blood, iron moves about bound to a molecule called transferrin. Transferrin carries iron (in its ferrous state) to the bone marrow and to other organs.
Most iron in the body is found in hemoglobin (in the adult male that accounts for approx.2300 mg; in the female, approx.1750 mg). Hemoglobin is the iron rich red blood cells, which carry oxygen from the lungs to the rest of the body (i.e. the muscles, organs, tissues). Once at its destination, it releases the oxygen to permit aerobic respiration to provide energy to power the required activity or function, in a process called metabolism.
Most of this circulating iron is taken up by red cell precursors and incorporated into heme (which is then combined with globin chains to make hemoglobin!). 85% of heme molecules are synthesized in bone marrow, the rest mostly in liver, but almost all body cells possess the ability to synthesize heme (Reference 1)
There are two storage forms of iron: ferritin and hemosiderin.
- Ferritin is the main storage form of iron. It is a protein which is released, and it is a useful measure of the tissue stores of iron (in other words, if you are iron rich in your tissues, your ferritin levels will be high). Iron can transfer in and out of this form quickly, which makes it easily accessible, but also means that it goes up in certain conditions, like chronic inflammation.
- Hemosiderin – made up of ferritin and cell debris – is a more stable form of iron storage, but is less readily accessible.
Measuring levels is a bit of a minefield, with lots of different markers indicating lots of different levels;
Haemoglobin is a protein responsible for transportation of oxygen in the blood. Normal male levels being between 13.5 and 17.5 grams per decilitre of blood, and normal female levels are 12.0 to 15.5 grams per decilitre of blood.
Haematocrit; this is the volume of red blood cells in blood. It is normally recorded as a percentage; 47% ±5% for men, 42% ±5% for women. The higher the ‘better’.