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In the light of the publicity last week on the BBC about inflammation being the cause of depression, we asked for an expert analysis of what this could mean. This is Tim Cantopher’s view.
Nothing about Major Depressive Disorder (MDD, Depressive Illness) is simple, least of all what causes it. Over the last year or two you may have heard or read that depression isn’t caused by hardship, stresses, losses or lack of transmitter chemicals in the brain, as had been thought, but by inflammation linked with unhealthy diet or other aspects of our toxic modern world. Like most specious statements this one contains a grain of truth.
A consistent finding in people suffering from Depressive Illness is a raised level of the antiinflammatory hormone cortisol. Successful treatment leads to a reduction in cortisol levels. Taking steroid hormones similar in action to cortisol can produce depressive symptoms. Other markers for inflammation (eg cytokines, C-Reactive Protein) are also commonly raised in blood taken from depressed patients and reduced after successful treatment. Omega-3 Fatty Acids, which have an anti-inflammatory action, have been shown by some studies to have a mild antidepressant effect. Anti-oxidants (which may reduce harmful inflammatory processes) in a healthy diet have been suggested to help in preventing depression. Vitamin D has an antiinflammatory action and deficiency, which is very common in Britain, has been linked to increased risk of depression.
All compelling evidence that Depressive Illness is caused by inflammation, right? Well, not really. If MDD were an inflammatory illness, like Rheumatoid Arthritis, then anti-inflammatory drugs like Ibuprofen and Naproxen should successfully treat it. They don’t and results with other anti-inflammatory drugs have been patchy. Taking Vitamin D supplements or high levels of antioxidants doesn’t reliably improve depressive symptoms. The benefits of Omega-3 Fatty Acid supplementation in MDD are far from convincing. So as yet, I wouldn’t advise you to rely on measures designed to fight inflammation to combat Depressive Illness. A combination of effective psychotherapy (Cognitive-Behavioral Therapy has the best evidence base) and antidepressants are still the treatment of choice for anything more severe than mild depression.
What is more interesting to me is the nature of the link between inflammation and depression. There are a number of theories, but the most plausible goes like this: Our ancestors, living on the primordial plane, had to adapt to a hostile environment in which danger and injury abounded. Natural selection took care of this adaptation. We are adapted for life on the primordial plane. So stress causes the immune system to gear up, increasing the activity of inflammatory processes, because the body is expecting to be injured and therefore to need to fight infection at the site of the wound(s). If the danger persists for more than a short period, the best chances of survival were served by a slowing of metabolic processes and withdrawal from the conflict (like hibernation in lower primates, but exhibiting as depression in the modern world). Cortisol takes care of that. If a child suffers a lot of stress and hardship through her formative years, she becomes more sensitive to stress later in life (there’s plenty of evidence for this) and is much more prone as an adult to produce both inflammatory reactions (for example asthma, eczema, gastritis, IBS and a hundred other stress-related inflammatory conditions) and also to a rise in cortisol linked to development of Depressive Illness. This is why stress early in life causes vulnerability to MDD.
So yes, inflammation and depression are linked, but beware those who tell you that the answer to Depressive Illness is a change in diet or some other panacea.