Dehydration leads to changes in the volume of compartments within the cranium that could put sportsmen and women at risk of brain damage after head injuries, according to a team of UK researchers (‘The effects of dehydration on brain volume – preliminary results’, International Journal of Sports Medicine 2005; 26:481-485).
In adults, the cranium (the part of the skull that encloses the brain) is a rigid bony vault of fixed size, with a constant volume that is the product of the volume of the brain, the intracranial cerebrospinal fluid (CSF) in a compartment known as the subarachnoid space, and the intra- cranial blood. The brain is suspended within the sub-arachnoid space, which surrounds it with a protective cushion of fluid. The brain itself contains fluid- filled cavities known as the cerebral ventricles, which communicate with the subarachnoid space.
The aim of this pioneering study was to investigate the relationship between dehydration and changes in the volume of the brain and the cerebral ventricles in six healthy male amateur rugby union players.
The subjects underwent magnetic resonance imaging (MRI) scans of the brain before and after a period of exercise designed to cause significant dehydration, while samples of blood and urine were taken before and afterwards to assess the degree of dehydration. One of the subjects (control) undertook a further series of MRI scans to enable the researchers to assess day-to-day fluctuations of brain and ventricular volume in a normally hydrated healthy person.
They found that the subjects lost between 2.1% and 2.6% of their body mass from sweating during the exercise. They also found a correlation between the degree of dehydration and the change in ventricular volume, with changes in the latter much larger than those seen in the normally hydrated control subject.
‘Changes in the volume of the brain, the intracranial CSF (especially the subarachnoid space) and the intracranial blood may influence the outcome of closed head injuries,’ the researchers explain. ‘After an impact to the head the brain will travel further within the cranium before it meets the skull if the subarachnoid space is enlarged than in the normally hydrated state. Consequently it will accelerate to higher velocities and this may increase the likelihood of contusion injuries after blows to the head such as those sustained in boxing, football and rugby’.
Although the researchers acknowledge that their study was too small to be definitive, they conclude that dehydration causes changes in the volume of intra-cranial compartments that may put sportsmen and women at increased risk of brain damage from contusion injury (bruising) and internal haemorrhage after head injuries.
‘Some sportsmen and women, eg boxers, rugby players and footballers, are especially vulnerable to serious head injuries whilst dehydrated.’