A major study that compared the psychiatric health and academic achievement of siblings gives strong support to the theory that dad’s biological clock exists and may be just as important as mom’s. Younger siblings are much more likely to suffer psychiatric disorders and academic difficulties than their older siblings.
Dr. Brian D’Onofrio led the study involving 2,615,081 people born in Sweden between 1973 and 2001. D’Onofrio is an associate professor at the Indiana University Department of Psychological and Brain Sciences. The results of his study — the largest and most comprehensive of all studies on how paternal age affects offspring — were published online in February by the medical journal, JAMA Psychiatry.
The Indiana study explored the effect of paternal age at childbearing in relation to specific measures:
- Attention-deficit / hyperactivity disorder (ADHD)
- Autism spectrum disorder (autism)
- Bipolar disorder
- Substance abuse
- Suicide attempts
- Failing grades
- Low educational attainment
When data analysis involved the general population, no significant trends emerged. Children born to older fathers were more likely to be diagnosed with some of the measures in the study but less likely for others.
The striking connections between fathers and their children occurred when siblings were compared. The sibling comparison revealed increased risk for all the measures used in the study and the increased risk was much higher than expected.
For example, comparing the psychiatric and academic health of children born when their fathers were 20 to 24 years of age to their younger siblings born when the father was 45 or older revealed:
- Autism — 3 times more likely in the children fathered later in the man’s life
- ADHD — 13 times more likely
- Bipolar disorder — 24 times more likely
D’Onofrio theorizes that gene mutations in the base pair of the man’s DNA occur more frequently as men age, the gene mutations occur during spermatogenesis, when the sperm is created, and that these mutations influence the neurological health of his children.
Previous studies have compared young fathers and older fathers but D’Onofrio likens that method to comparing apples and oranges. His study looked at the neurological health of children born to the same father over time. D’Onofrio says doing so “enables us to get a better understanding of what’s truly due to the advancing father’s age at childbearing.”
In 2012, researchers in Iceland studied the effects of paternal age to the rate of autism and schizophrenia in his children. Of the 78 genomes that were examined for this study, the increased risk for autism and schizophrenia by 20% to 30% was linked to father’s age.
Source: D’Onofrio, Brian M., PhD, et al. “Paternal Age at Childbearing and Offspring Psychiatric and Academic Morbidity (abstract).” JAMA Psychiatry. The JAMA Network / American Medical Association. Feb 26, 2014. Web. Mar 7, 2014.