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What is already known on this topic?
There is robust evidence of an increased risk for autism, schizophrenia and learning disabilities in children born to older fathers, and an increased risk for Down's syndrome in children born to older mothers.1 Advanced parental age may prompt mental disorders in the offspring via de novo mutations in the male germline or chromosomal abnormalities in the female gamete.2 On the other hand, the children of young parents more frequently display conduct disorders and poor outcomes, such as substance use or academic problems, a finding that has been attributed to the socioeconomic deprivation and mental health difficulties affecting teenage mothers as described by McGrath et al.
What this paper adds?
Most previous studies had examined the effect of extreme parental ages in clinical samples with regard to a particular mental disorder; rarely had assessments been conducted across diagnostic categories.1
Their results confirm the risks of delaying paternity but, unlike recent reports, fail to find an association between paternal age and the occurrence of bipolar disorder or schizoaffective disorder in the offspring.2
Most interestingly, almost all mental disorders, except for eating disorders and schizoaffective disorders, were more strongly associated with teenage or young mothers than they were with the reference age group (25–29 years). Inversely, a maternal age between 30 and 40 years showed a protective effect with regard to several mental disorders.
Although the results were adjusted for some key variables, they did not account for the effect of the educational and socioeconomic level of the parents.
The low rates of teenage pregnancy and the importance of social welfare systems in Denmark could limit the generalisability of the results.
There is no reliability information on the clinical diagnoses or any attempt to compare with structured interviews. An analysis of the characteristics of the diagnosticians could have also been useful.
What next in research?
Future research could explore the mechanisms by which socioeconomic factors mediate the effect of advanced and young parental age on the intellectual performance and mental health of the offspring.2 Correlates of early maternal age and late paternal age may vary in different countries and societies. Similar studies in developing countries are therefore needed.
Do these results change your practices and why?
Yes, this study raises awareness of the possible risks associated with overly late or early parenthood and should inform the advice given to future parents. The impact of early childbearing is particularly relevant from a public health perspective because it has been partially disregarded until now.
ABSTRACT FROM: McGrath JJ, Petersen L, Agerbo E, et al. A comprehensive assessment of parental age and psychiatric disorders. JAMA Psychiatry 2014;71:301–9.
Patients/participants 2 894 688 individuals born in Denmark between 1 January 1955 and 31 December 2006, whose parents were also born in Denmark. Individuals with an existing diagnosis of any psychiatric disorder (pre-1995) were excluded from the study, as were those who were no longer living in Denmark as of 1995.
Setting Denmark; 1995–2011.
Exposure Maternal and parental age at time of offspring birth.
Comparison Risk of incident psychiatric diagnosis was compared across a range of parental ages (ie, mother's or father's age at offspring's birth). Assessed parental age groups included 12–19, 20–24, 30–34, 35–39, 40–44 and >45 years; parental age of 25-29 years served as the reference category for all comparisons.
Follow-up period 17 years.
Overall, 2 894 688 individuals were followed up for 42.7 million person-years, and 218 441 cohort participants had a first psychiatric disorder diagnosis during that time.
Any psychiatric diagnosis (ICD-10-DCR, recorded in the population-wide Danish Psychiatric Central Research Register (DPCRR)) Offspring of mothers with lower maternal age had significantly higher incidence rate ratio (IRR) for any psychiatric diagnosis. Offspring of older maternal age groups had significantly lower risk of any incident psychiatric diagnosis. The relationship with paternal age was U shaped, with significantly higher IRR for younger and older paternal age. See the WebExtra table for IRR data across parental age groups and outcomes.
Mental or behavioural disorders due to psychoactive substance abuse (ICD-10-DCR)
Offspring of young parents (maternal or paternal age 12–19 years) had significantly higher IRR of disorders related to substance abuse (including alcohol and cannabis); a smaller but still statistically significant increase in IRR was also observed with older fathers. When assessed by particular substance among the parental age category of 12–19, the risk of incident disorders due to cannabis tended to be higher than those due to alcohol use (maternal: alcohol IRR=1.51 (95% CI 1.43 to 1.59), cannabis IRR=2.22 (95% CI 2.05 to 2.41); paternal: alcohol=1.39 (95% CI 1.29 to 1.51), cannabis IRR=1.58 (95% CI 1.40 to 1.79)).
Schizophrenia and related disorders (ICD-10-DCR) Older paternal age was associated with increased risk of incident schizophrenia and related disorders; the association was significant for paternal age categories over 35 years and particularly among those aged 45 or older. Conversely, these disorders were associated with younger maternal age.
Hyperkinetic disorders (ICD-10-DCR) Younger maternal age was associated with increased risk of hyperkinetic disorders, while older maternal age was associated with significantly reduced IRR compared to age 25–29. The relationship with paternal age was U shaped, with significantly higher IRR among younger and older fathers.
This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.
Files in this Data Supplement:
- Data supplement 1 - Online table
Competing interests None.
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