Depression 'lowers disease immunity'

Poor resistance to disease is common among older people

The ability to fend off disease can be reduced by older adults suffering from persistent mild depression, research suggests.

The US-based study found that such patients are not producing enough white blood cells to fight off infection.

Depression is estimated to affect up to 57% of older adults for some period of their lives.

The study suggests that earlier detection of even mild depression is crucial if the knock-on effect of lowering a person's immune system is to be combated.

It seems that it is the length of time of the depression, not the severity that is affecting a person's immunity

Lynanne McGuire, lead researcher

During the study, reported in the February edition of the Journal of Abnormal Psychology, researchers looked at a group of 78 adults with an average age of 72.5.

It compared 22 patients suffering from chronic depression with 56 non-sufferers, on their ability to generate enough white blood cells to fight off infection.

Poor immunity

The participants were taking part in a larger study looking at the stress and health of carers of dementia sufferers. They were a mixture of carers and non-carers.

The results showed that those with chronic mild depression had low T cell response to laboratory-produced infection when they were re-assessed 18 months later.

T cells and their performance are the most reliable gauge of a person's ability to fight off foreign bodies such as viruses and bacteria.

The older the person, the poorer the immune response was found to be.

It's too early to start flag-waving but this is certainly good laboratory evidence and it is important because it is testable

Dr Mike Isaac, Institute of Psychiatrists

The information, together with previous research, showed depressive symptoms could increase the typical immune system decline which accompanies ageing.

Lead researcher Lynanne McGuire of the John Hopkins School of Medicine said: "In this study, it seems that it is the length of time of the depression, not the severity, that is affecting a person's immunity."

She said changes in immunity have been associated with both depression and ageing, particularly in those over 60.

Other factors can also affect a person's resistance to infection and a lack of social support was highlighted as a risk factor for depression in the report.

'Testable'

The research was greeted with enthusiasm by Dr Mike Isaac, a consultant psychiatrist and member of the Institute of Psychiatrists.

He said: "It has never been absolutely clear which comes first, people with long-term illnesses becoming depressed or their immune system being affected by the depression.

"It's too early to start flag-waving but this is certainly good laboratory evidence and it is important because it is testable."

He said the results reflected what he and other clinicians have found in practice.

"The problem has been the evidence has so far only been anecdotal," he added.

Detection essential

Dr McGuire conducted the study with co-authors Janice K Kiecolt-Glaser and Ronald Glaser of the Ohio State University College of Medicine.

They suggest the effect of mild depression on the immune system is linked to the increased risk and severity of infections and cancer found in older adults.

Spotting and treating even mild depression in this age group may be essential to achieving better health in older people, they add.

The Journal of Abnormal Psychology is published by the American Psychological Association (APA), the largest professional organisation representing psychology in the US and the world's largest association of psychologists.