Patients with major depressive disorder had more signs of inflammation in the brain than healthy people, scientists at the University of Manchester have found.

There are about 6,000 suicides in the UK and Ireland each year, and about 55,000 in the EU, according to the Mental Health Foundation. More than 90% of suicides have been associated with a psychiatric disorder. The highest rates of suicide are among those with depressive disorders.

Depression is a mental health problem that has physical symptoms in the brain. Inflammation has been consistently linked to depression in studies for several years. But pinpointing whereabouts this depression is in the body or brain hasn't been easy.

Inflammation in the brain is worst among depressed patients who are having suicidal thoughts, a study in Biological Psychiatry has now found.

"We were really struck by the difference between patients who were suicidal at the time and those who were not. Even if they had similar overall depression rating scores, the people who were having suicidal thoughts had much higher levels of those inflammatory markers," study author Peter Talbot of the University of Manchester told IBTimes UK.

The inflammation was picked up by noting activation of the brain's microglial cells, which make up about 10% of cells in the brain, during PET scans of patients' brains. These are the cells responsible for the immune defence of the central nervous system. It's possible that the depression-linked inflammation may be happening elsewhere in the brain.

More fine-grained data on where the inflammation is in suicidal patients – and those with depression more broadly – isn't an easy task. But one region called the anterior singulate appears to be involved. The anterior singulate plays a crucial role in mood regulation and cognitive function.

Microglial inflammation has been linked to depression before, but mainly in brain tissue samples from patients after death. This is the second time it's been linked to depression in living patients, as well as the first to have found an association with suicidal thoughts.

The finding suggests that anti-inflammatory medication may have antidepressant effects in some patients. However, not all patients with depression have brain inflammation.

Talking therapies, antidepressants, a healthy diet and exercise are current treatments for depression. But for many patients, none of these therapies are effective. Anti-inflammatories could be another option. A previous study has found that a drug for rheumatoid arthritis was an effective augmentation to standard treatments for depression.

"Already data are starting to suggest that some patients' depression may be responsive to anti-inflammatory drugs," Talbot said. "So it may be in the future we're not using anti-inflammatory drugs for everyone, but we're identifying a sub-population whose depression is particularly associated with inflammation and using it to treat them."

There are about 6,000 suicides in the UK and Ireland every year. Gerald Gabernig