Blood flow to the brain significantly affected by dehydration

It’s a lesson riders in the Tour de France know all too well – drinking water while cycling in extreme heat is vital if they are to remain at peak performance.

Now a new study shows that not only does dehydration significantly reduce blood flow to the brain – but the brain itself has a remarkable coping mechanism to keep athletes going.

Using new techniques, researchers at Brunel University have demonstrated for the first time that, when people are dehydrated through exercise, they experience a fast and significant fall in blood flow and oxygen delivery to the brain.

However, rather than shutting down, the brain cleverly reacts by increasing oxygen extraction from the circulation and giving itself just enough to keep functioning.

Researcher at Brunel and first author of the study Steven Trangmar said: “This research has helped us understand a lot more about how the human brain responds to extreme exercise in extreme conditions. We can now see that blood flow to this vital organ is significantly affected by dehydration.”

“But we can also see that this is when the brain kicks in, preserving its own oxygen consumption to ensure it sustains its function.”

José González-Alonso, Professor of Exercise and Cardiovascular Physiology at Brunel, said:

These findings show that the brain has remarkable ways of protecting itself from extreme circumstances, however they also clearly substantiate the recommendation that people should ingest fluids during exercise to help optimise physiological function and performance.

Researchers used Doppler ultrasonography and catheters inserted in the brachial artery and internal jugular vein to assess blood flow. Measurements were taken from 10 trained male cyclists during incremental cycling to exhaustion in a hot environment.

The study showed that dehydration reduced body mass, increased internal body temperature, lowered brain blood flow and impaired exercise capacity.