PHILADELPHIA — Seasonal allergies might be associated with fatigue and mood disorders, including depression, in certain patients, Dr. Tedor T. Postolache reported at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.
These possible associations are suggested by a series of observational studies documenting the correlation of a spike in suicides during the spring months and the sudden release of tree pollens after the relatively pollen-free winter, said Dr. Postolache, a psychiatrist and director of the mood and anxiety program at the University of Maryland, Baltimore.
Allergies that occur at other times of the year might have the same effect, but the impact of tree pollen on suicide rates can be seen in large populations because it is so dramatic after winter. Dr. Postolache and his associates first reported on a possible link between the tree pollen season and an increased suicide rate in women several years ago (Molecular Psychiatry 2005;10:232–5).
“Allergens may generate an immune response in vulnerable individuals, with inflammatory processes reaching brain centers involved in modulation of risk factors for suicide,” he said at the meeting.
Among the evidence that links allergy and depression is a 1999 study of more than 6,800 adults that showed that patients with hay fever were twice as likely to have been diagnosed with major depression in the past 12 months.
In the same group, those participants with a history of receiving allergy shots or having a positive skin test reaction were more than three times as likely to have been diagnosed with major depression in the same time.
A population-based study of an unselected group of more than 12,000 Finns born in 1966 found that maternal atopy was linked with an almost twofold increased risk for depression in women at any time in life. Women who themselves were diagnosed with atopy and also had a mother with atopy had a fourfold increased risk of developing depression, compared with nonatopic women with nonatopic mothers (J. Allergy Clin. Immunol. 2003;111:1249–54).
A link between allergy and suicide was recently explored by Dr. Postolache and Danish collaborators (including Dr. Ping Qin, an epidemiologist at Aarhus (Denmark) University in a study of more than 21,000 Danes who committed suicide during 1981–1997. The medical data were obtained through the National Patient Register in Denmark. In this case-control analysis, data were obtained for 20 control individuals for every suicide case by randomly finding people from Danish records who lived at the same time, and matching for gender and age.
Preliminary analysis of these data indicated that men and women had a similarly increased risk for suicide that was linked to having allergies.
Among all people in the study, those with an allergy were about two times more likely to have committed suicide, compared with similarly aged people without history of an allergy, Dr. Postolache said. He and his associates now are in the process of adjusting this risk ratio for potential confounders, such as psychiatric history, socioeconomic status, and family history of allergy.
Dr. Postolache suggested some possible physiological mechanisms that could mediate the link between allergies, especially aeroallergen allergies, and psychiatric effects, based on evidence from animal studies. Cytokines released in the nose because of an allergic reaction can activate indoleamine 2,3-dioxygenase, which inhibits serotonin production. Cytokines in the nose also may upset the hypothalamic-pituitary-adrenal axis. Nasal cytokines can affect the brain through signals sent via the vagus and olfactory nerves.
Those with an allergy were more than twice as likely to have committed suicide than were those without allergy. DR. POSTOLACHE