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May 6, 2008 (Washington, DC) - Analysis of a major population-based study of
mental health suggests an association between allergies and suicidality.

Using data from the National Comorbidity Survey Replication (NCS-R),
researchers showed a significant association between allergies and a history
of suicide ideation and between allergies and a history of suicide attempts
that remained significant even after they controlled for depression.

"This is similar to previous results showing significant relationships
between both asthma and dermatitis and suicide ideation and suicide
attempts," the researchers, with coauthor Stephen Welch, MD, from the
Medical College of Georgia, in Augusta, write.

Their report was presented here at the American Psychiatric Association
161st Annual Meeting.

History of Allergies and Suicide Ideation

The study used data from the NCS-R, a national representative sample of 9882
English-speaking people aged 18 years or older living in US households
between 2001 and 2004, funded by the National Institute of Mental Health.

Part 1 of the survey, comprising the core diagnostic assessment, was
administered to all respondents, and Part 2 only to those individuals who
met lifetime criteria for a Part 1 disorder, as well as a probability sample
of other respondents.

Logistic regression models were used to calculate adjusted odds ratios with
95% confidence intervals after researchers controlled for confounding
variables, including age, sex, race, and a history of depression.

Their results showed a positive and significant correlation between a
history of allergies and suicidal ideation, with an adjusted odds ratio of
1.37 (95% CI, 1.13 - 1.65), they note. After they controlled for depression,
the odds ratio was 1.27 (95% CI, 1.04 - 1.54).

The correlation with a history of suicide attempts was even greater, with an
adjusted odds ratio of 1.40 (1.07 - 1.84), falling to 1.32 (1.003 - 1.74)
after they controlled for depression.

The researchers postulate several different theories on the association, Dr.
Welch told Medscape Psychiatry. "Is this just a quality-of-life issue? Is
this something to do with personality? Or is there a biochemical basis
behind it?" he said.

Previous studies that looked at whether personality traits might simply lead
some people to be more likely to report both depression and allergies did
not find a correlation, according to the paper. Nor did a study of possible
association between increased levels of immunoglobulin E (IgE), the authors
write.

"The most promising research seems to be with increased cytokine activity in
the body," said Dr. Welch. Research is looking at their possible
relationship to depression. Other studies have shown increased cytokine
levels in the brains of suicide victims.

Future Research

Right now, Dr. Welch said of the allergy-suicidality link they are reporting
here: "It's not a major correlation, so it would be unlikely that this would
be of big clinical significance, in terms of: 'Do I need to screen for
allergy when I am in the emergency room assessing someone for suicidality?'

"There are more important risk factors that have a much greater level of
significance, such as a history of depression, history of previous
attempts," he explained.

However, he said, if research can look at homogeneous groups of people - for
example, groups of the same sex, age, race, and history of previous illness
- to limit the number of variables that could be influencing the situation,
"We would hope that that would give us a lot more insight into what is going
on, and it would give us a good place to start attacking in terms of how can
we treat this effectively."

Questions for future research, said Welch, include whether the association
would remain significant if the data were controlled for other illnesses,
including asthma.

In addition, he said, longitudinal studies looking at severity of symptoms
might provide further support. "If you find that as allergy symptoms
increase, the intensity of suicide ideation, the number of attempts,
increases, that would lend evidence to the allergies causing the
suicidality," Dr. Welch added.

Some work, he noted, does indicate that peaks in tree pollen correlate with
certain types of suicide attempts. If suicide attempts go down with
treatment for asthma and allergy symptoms, "that would also lend some more
credence," he added.

Future research for his group, he said, may include looking at the data
while controlling for asthma and some of the other Axis I disorders.

The study was supported by the National Institute of Mental Health.

American Psychiatric Association 161st Annual Meeting: Abstract NR2-030.
Presented May 5, 2008.