Parental history of psychiatric diagnoses and unipolar depression: a Danish National Register-based cohort study.

BACKGROUND: Depression is known to run in families, but the effects of parental history of other psychiatric diagnoses on depression rates are less well studied. Few studies have examined the impact of parental psychopathology on depression rates in older age groups. METHOD: We established a population-based cohort including all individuals born in Denmark after 1954 and alive on their 10th birthday (N = 29 76 264). Exposure variables were maternal and paternal history of schizophrenia, bipolar disorder, depression, anxiety or 'other' psychiatric diagnoses. Incidence rate ratios (IRRs) were estimated using Poisson regressions. RESULTS: Parental history of any psychiatric diagnosis increased incidence rates of outpatient (maternal: IRR 1.88, p < 0.0001; paternal: IRR 1.68, p < 0.0001) and inpatient (maternal: IRR 1.99, p < 0.0001; paternal: IRR 1.83, p < 0.0001) depression relative to no parental history. IRRs for parental history of non-affective disorders remained relatively stable across age groups, while IRRs for parental affective disorders (unipolar or bipolar) decreased with age from 2.29-3.96 in the youngest age group to 1.53-1.90 in the oldest group. IRR estimates for all parental diagnoses were similar among individuals aged ⩾41 years (IRR range 1.51-1.90). CONCLUSIONS: Parental history of any psychiatric diagnosis is associated with increased incidence rates of unipolar depression. In younger age groups, parental history of affective diagnoses is more strongly associated with rates of unipolar depression than non-affective diagnoses; however, this distinction disappears after age 40, suggesting that parental psychopathology in general, rather than any one disorder, confers risk for depression in middle life.

Allergy is associated with suicide completion with a possible mediating role of mood disorder - a population-based study.

BACKGROUND: With increasing research suggesting a role of allergy on suicidality, this study, on a population level, delved into how allergy affects risk for suicide completion in the context of mood disorder and other factors. METHODS: Based on the entire population of Denmark, we included 27,096 completed suicides and 467,571 live controls matched on sex and age with a nested case-control design. We retrieved personal information on hospital contacts for allergy and other variables from various Danish longitudinal registries and analyzed the data with conditional logistic regression. RESULTS: We noted that 1.17% suicide victims, compared with 0.79% matched controls, had a history of hospital contact for allergy and that a history of allergy predicted an increased risk for suicide completion; however, the effect was confined to allergy that led to inpatient treatment (IRR: 1.59, 95% CI: 1.41-1.80). The increased risk was attenuated somewhat but remained significant when adjusted for personal psychiatric history and socioeconomic status. Meanwhile, we observed a nonsignificantly stronger effect in women than in men, and a significant age difference with a stronger effect for individuals at high ages. Moreover, we detected a significant interaction between allergy and mood disorder - even an antagonism effect of the two exposures. Allergy increased suicide risk only in persons with no history of mood disorder, whereas it eliminated suicide risk in those with a history of mood disorder. CONCLUSIONS: The findings support a link between allergy and suicidality, with a possible mediating role of mood disorder.