Many hikers and mountain climbers say their love of the sport is a spiritual experience that clears the mind, but that analogy may be a bit too real. A new study finds high altitude mountain climbing alters the brain.

Magnetic resonance images or MRIs were performed on thirty-five mountain climbers: twelve professionals and twenty-three amateurs. They all recently attempted high altitude climbs - including Mount Everest, the world's highest peak. Virtually everyone who climbed Everest showed signs of brain damage, and many of the others as well. The MRIs revealed microhemorrhages in the brain.

The worst cases were climbers who had suffered high-altitude cerebral edema. This happens when capillaries in the brain leak, causing dangerous swelling. A quick fix is rapidly descending the mountain or using a hypobaric chamber.

Scientists had always thought once a climber recovered, the brain healed. But the new study suggests the damage is permanent, and revealed even climbers of lesser peaks who showed no signs of altitude sickness had irregular MRIs.

The scans showed an enlargement of the Virchow-Robin or VR spaces. These spaces surround blood vessels that drain brain fluid and communicate with the lymph system. Usually, an enlargement of VR spaces happens in the elderly, but not young people, such as the mountain climbers in the study. Three years after the initial MRI, these same climbers who had made no expeditions in the interim, still had the same brain scans, suggesting the damage is permanent.

Scientists will need to study a greater number of climbers to conclude whether high-altitude mountaineering leads to long-term brain damage and diseases such as Alzheimer's. As the sport gains popularity, climbers should know the full risks.