People with severe nasal or skin allergies may have a higher suicide risk than the allergy-free, a new study suggests — although the reasons are not yet clear.
Reviewing medical records for more than 27,000 suicide victims, Danish researchers found that just more than 1 percent had ever been hospitalized for severe nasal allergies or eczema. That compared with 0.8 percent among nearly 468,000 adults studied for comparison.
When the researchers weighed other factors — like people's incomes and history of mental health disorders — those treated for severe allergies had a one-third higher risk of suicide than people with no history of allergies.
While that difference sounds large, the risk to any one person with serious allergies would still be quite small.
"We did find an increased risk for suicide associated with severe allergy — however, the risk is not particularly high," said lead researcher Dr. Ping Qin, of Aarhus University in Denmark.
So allergy sufferers, Qin said in an e-mail, should not be alarmed.
The findings, published in the journal Allergy, are in line with a recent study from Taiwan linking asthma symptoms with suicide risk. But researchers are not completely sure why these connections exist.
In the current study, people who had only ever received outpatient treatment for milder nasal allergies or eczema showed no increased suicide risk.
Instead, the link was confined to people who at some point needed inpatient treatment — to manage, for instance, a severe asthma attack related to nasal allergies.
But Qin's team speculates that the suicide risk is not only a matter of people with serious allergies feeling worse.
During allergic reactions, the brain churns out substances called pro-inflammatory cytokines — proteins that help cells communicate with each other. And research shows that these cytokines can have depression-promoting effects, such as dips in the brain's production of the "feel-good" chemical serotonin.
So it's possible that such effects on the nervous system play a role, the researchers say.
But Qin's team also found that the picture became more complicated when they looked at people's mental health history.
Severe allergies, it turned out, appeared related to suicide risk only among people who had never been treated for depression or anxiety disorders. Compared with this group, people who had ever been treated for both severe allergies and depression/anxiety actually had a lower suicide risk.
According to Qin, this raises the question of whether mental health problems in people with severe allergies are going unrecognized, whereas diagnosing and treating them can lower their odds of suicide.
Certain antidepressants, the researchers note, not only ease depression symptoms, but also seem to suppress those same inflammatory cytokines released during allergic reactions.
None of this, however, means that people with allergies need to be screened for suicidal thoughts and behavior, Qin's team says.
But, they write, "the results suggest that physicians treating patients with allergic disorders should be vigilant about expressions of suicidal ideation or signs of self-harm, particularly for those with a recent diagnosis or severe allergy."
One of the limits of the current study is that the researchers had no information on the specific allergy or psychiatric treatments people had received.
Qin said more studies are needed to look at how various antidepressants and allergy drugs might affect suicide risk in allergy sufferers.
In recent years, there have been reports of depression, suicidal thoughts and other psychiatric problems in some people on allergy medications known as leukotriene modifiers — including Singulair, Accolate and Zyflo. But whether the drugs themselves are to blame remains unclear.
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