Bipolar disorder results in loss of brain tissue, research published today reveals.
The four-year study examined 21 patients with the illness along with a control group.
The patients' brains were scanned at the beginning and end of the research.
In the interval, all had experienced at least one episode and some as many as six.
They found that every patient had lost grey matter in the temporal lobe and the cerebellum, the areas of the brain associated with memory and coordination.
Study leader Dr Andrew McIntosh said it remained unclear whether the loss of brain tissue was a cause or consequence of the disease.
"It may be that repeated episodes of illness harm the brain and lead to the decline," he said.
"Another possibility is that the brain changes are caused by stress or genetic factors, which tend to lead both to more frequent illness episodes and to greater brain loss.
"No matter which way round it is, it emphasises in my mind the importance of maintaining people in remission and the importance of getting them the best treatment."
Bipolar disorder affects half a million people in the UK. Sufferers experience successive episodes of mania followed by deep depression.