Severe sleep apnea can lead to brain damage, and fortunately, it can be reversed. However, the time it takes to reverse the damage caused by sleep apnea is different in every situation and is highly dependent on the severity of sleep apnea, how long it has been present, and the overall health of the patient. Results from studies looking at the link between brain damage and sleep apnea show that participants with severe, untreated sleep apnea had a significant reduction in white matter fiber integrity in multiple areas of the brain; this brain damage was characterized by impairments to cognition, mood changes and a reduction in daytime alertness. Three months of CPAP therapy produced limited improvements to damaged brain structures, however, after 12 months of CPAP therapy, it led to an almost complete reversal of white matter abnormalities. Treatment also produced significant improvements in mood, alertness, quality of life, and nearly all cognitive tests.