SACRAMENTO, September 18 — A study of 6,336 California grandparents has found that a grandfather’s smoking and drinking habits are associated with an increased risk of autism spectrum disorder in his grandchildren, according to research published in a peer-reviewed journal. The analysis drew on data from the California Department of Public Health’s California Autism Twins Study and other sources, and focused on grandparents’ lifestyle exposures — specifically smoking and alcohol consumption — and their potential transgenerational effects on neurodevelopment.
Among the grandparents studied, those who reported consuming five or more servings of hard liquor per week had nearly three times the risk of having a grandchild with autism compared with non-drinkers. Grandparents who smoked 20 or more cigarettes per day had roughly twice the risk.
The researchers controlled for potential confounders including parental age, socioeconomic status, and maternal smoking during pregnancy. The findings suggest that paternal grandfathers’ exposures may be particularly relevant, though the study did not find a statistically significant association for maternal grandmothers’ exposures.
Observational findings, not proof of cause
The study’s authors emphasize that the results are observational and do not prove causation. They add to a growing body of evidence that environmental exposures can have effects across generations, possibly through epigenetic mechanisms. Autism spectrum disorder is a developmental disability characterized by challenges with social communication and repetitive behaviors.
According to the Centers for Disease Control and Prevention, approximately 1 in 36 children in the United States is diagnosed with ASD, with boys being four times more likely than girls. The study’s limitations include reliance on self-reported exposure data and the potential for recall bias.
The authors note that the absolute risk increase is small, but the population attributable risk could be significant given the prevalence of smoking and drinking. The findings were adjusted for multiple comparisons, with effect sizes reported as odds ratios with 95% confidence intervals, and were consistent across sensitivity analyses.
What the research adds
The work is consistent with the Developmental Origins of Health and Disease hypothesis, which holds that environmental exposures during critical periods of development can have long-lasting effects. It also adds to previous research linking parental exposures to autism risk, such as the association between maternal smoking during pregnancy and autism, though some studies have shown mixed results. The study was conducted in California, which has a diverse population and a large sample size, but the results may not be generalizable to other populations.
The authors call for replication in other cohorts, and recommend that healthcare providers counsel men of reproductive age about the potential risks of smoking and heavy drinking. The findings have implications for public health messaging, suggesting that reducing smoking and heavy drinking among men of reproductive age could have benefits for future generations.
The encouraging part is that this is a modifiable exposure — unlike genetics, smoking and heavy drinking are behaviors that men can change. The study’s authors conclude that grandpaternal smoking and drinking may be associated with autism risk in grandchildren, but further research is needed to confirm these findings and elucidate the underlying mechanisms. Watch for replication studies in other populations and for work exploring the biological pathways involved. Consult your doctor for medical advice.
