Naturalistic exposure to tree pollen in spring: A positive relationship between depression, anxiety and allergy symptom changes in patients with recurring mood disorders

In order to consider the evidence for an association between allergy, allergens, depression and anxiety symptoms we hypothesized that patients with recurring mood disorders who are sensitized to tree pollen, in comparison to those who are not sensitized, will report larger negative changes in mood during exposure to tree pollen in spring. We have also hypothesized that changes between low and high tree pollen periods in self-reported allergy symptoms will correlate positively with changes in self-reported depression scores. We present 1-year preliminary data on the first 51 patients with unipolar or bipolar disorder (age: 19-63 years, 65% female). All tree- pollen IgE positive subjects (12) were included in the experimental group and patients negative to a multi-allergen serological test were included in the control group. Ratings of mood and allergic disease status were performed once during the period of high airborne pollen counts and once during a period of low airborne pollen counts, as reported by two local pollen-counting stations. Linear regression models were developed to examine potential associations between changes in depression and anxiety scores (dependant variable) and tree pollen sensitization, and changes in the allergy symptom severity score and their interactions with gender and order of testing. We did not confirm the hypothesized relationship between a specific tree pollen sensitization and changes in mood during tree pollen exposure; however, we did confirm the hypothesized positive relationship between the changes in allergy symptoms and changes in subjects’ depression scores (adjusted p<0.05) and significant positive association between changes in allergy scores and changes in anxiety scores (p< 0.04). This is consistent with previous epidemiological evidence connecting allergy with depression and anxiety, as well as our recent reports of increased expression of cytokines in the prefrontal cortex in victims of suicide and in experimental animals sensitized and exposed to tree pollen. Larger clinical samples with measurements of molecular and cellular markers of inflammation are necessary to better understand the allergy-depression relationship, and for potentially developing interventions to prevent and treat environmentally induced exacerbations in mood disorders.