a1 Department of Preventive Medicine, University of Sao Paulo, Brazil
a2 Academic Unit of Psychiatry, Department of Community Based Medicine, Faculty of Medicine, University of Bristol, Bristol, UK
a3 Child and Adolescent Public Health Epidemiology Group, Karolinska Institute, Stockholm, Sweden
a4 Department of Psychological Medicine, Cardiff University, Cardiff, UK
a5 Department of Social Medicine, University of Bristol, Bristol, UK
Background A consistent association between paternal age and their offspring's risk of schizophrenia has been observed, with no independent association with maternal age. The relationship of paternal and maternal ages with risk of bipolar affective disorders (BPAD) in the offspring is less clear. The present study aimed at testing the hypothesis that paternal age is associated with their offspring's risk of BPAD, whereas maternal age is not.
Method This population-based cohort study was conducted with individuals born in Sweden during 1973–1980 and still resident there at age 16 years. Outcome was first hospital admission with a diagnosis of BPAD. Hazard ratios (HRs) were calculated using Cox's proportional hazard regression.
Results After adjustment for all potential confounding variables except maternal age, the HR for risk of BPAD for each 10-year increase in paternal age was 1.28 [95% confidence interval (CI) 1.11–1.48], but this fell to 1.20 (95% CI 0.97–1.48) after adjusting for maternal age. A similar result was found for maternal age and risk of BPAD [HR 1.30 (95% CI 1.08–1.56) before adjustment for paternal age, HR 1.12 (95% CI 0.86–1.45) after adjustment]. The HR associated with having either parent aged 30 years or over was 1.26 (95% CI 1.01–1.57) and it was 1.45 (95% CI 1.16–1.81) if both parents were >30 years.
Conclusions Unlike schizophrenia, the risk of BPAD seems to be associated with both paternal and maternal ages.
(Received July 25 2008)
(Revised May 17 2009)
(Accepted June 11 2009)
(Online publication July 23 2009)
c1 Address for correspondence: Professor F. Rasmussen, Child and Adolescent Public Health Epidemiology Group, Department of Public Health Sciences, Karolinska Institute, SE-17176 Stockholm, Sweden. (Email: firstname.lastname@example.org)