The most interesting session I attended at AAAAI 2008 was entitled ‘Neuroimmunologic Consequences of Allergic Inflammation.’
How do allergies affect your brain and mood?
We all know that allergies can make people feel miserable. Therefore, a link between allergies and depression is not surprising.
However, you may be surprised to learn that peaks in tree pollen counts are associated with spikes in suicide.
It appears that the connection between allergies and depression runs deeper than the obvious fact that allergies make people feel bad.
When allergies activate the immune system, the brain begins to produce pro-inflammatory cytokines. Cytokines are signal proteins that allow cells to communicate with each other. Pro-inflammatory cytokine expression can lead to reduced activity and social interaction, inhibition of sexual behavior, reduced food intake, increased sleepiness, and altered REM sleep.
Pro-inflammatory cytokines also activate the HPA axis in the brain. The HPA axis consists of the hypothalamus, the pituitary gland, and the adrenal gland. By sending and receiving hormones and other signals, the HPA axis controls reactions to stress and regulates digestion, immune responses, sexuality, mood, and energy.
One hypothesis states that activation of the HPA axis results in aberrant responses to stress. In other words, allergies not only make you feel bad, but they could also make you overreact to stressful situations. One UCLA study found that subjects with a history of allergy were three times more likely to have both major depression and lower back pain. Researchers hypothesized that allergies may prime the HPA axis to respond more strongly to stressors like back pain.
Non-physical stressors, for example, may include the death of a loved one or loss of a job. If allergies cause the brain to overreact to stress, then it's easy to imagine how suicide rates increase during peak tree pollen season.
Note that clinical depression involves much more than feeling bad; it's deeper than reduced activity, increased sleepiness, and all the other feelings that go along with being sick. Depression involves dysphoria (extremely low mood) or anhedonia (an inability to experience pleasure), and it can significantly affect work, family, school, sleep, health, and life. Clinical depression can also lead to suicide.
According to Dr. Teodor Postolache, MD, one allergy patient out of 500 will attempt suicide. Allergists, allergy nurses, and other healthcare practitioners should look for signs of clinical depression among patients and try to differentiate them from the mood changes that typically occur with sickness. Signs of clinical depression include hopelessness, helplessnes, excessive guilt, and worthlesness.
Do allergies cause depression and suicide? No – but allergy sufferers are at increased risk, and allergic disease is one more straw on the camel's back. If you can eliminate that one straw – by relieving allergies with environmental control, immunotherapy, or medication – then the chance of suicide is greatly reduced.
However… Also be aware that some allergy medications, like antihistamines, decongestants and corticosteroids, can make depression worse for certain patients. Use of the allergy medication Singulair has recently been linked to suicide.
USA Today recently published an article about seasonal allergies and depression: Seasonal Allergies Could Spark Depression, Fatigue.