Boys exposed to at least 2 hours a day of screen time by 1 year of age were significantly more likely to have an autism spectrum disorder (ASD) diagnosis at 3 years, based on data from more than 80,000 children.
The World Health Organization and the American Academy of Pediatrics recommend against any screen time for infants up to 1 year of age and 18 months of age, respectively, wrote Megumi Kushima, MA, of the University of Yamanashi (Japan), and colleagues on behalf of the Japan Environment and Children's Study Group.
The extent to which screen time duration in infancy is associated with subsequent ASD diagnosis remains unclear, the researchers said. The ongoing COVID-19 pandemic has increased screen time among children worldwide, which makes an examination of the impact of screen time on children's health an important public health issue.
In a study published in JAMA Pediatrics, the researchers recruited pregnant women between 2011 and 2014; data were analyzed in December 2020. The final study population included 84,030 mother-child pairs. The primary exposure of screen time at 1 year of age was assessed by questionnaire, in which mothers were asked to report their number of hours they let their child watch TV or DVDs daily. Responses were none (no screen time), less than 1 hour, 1 hour or more but less than 2 hours, 2 hours or more but less than 4 hours, and 4 hours or more.
The primary outcome was ASD diagnosis at 3 years of age, and mothers were asked via questionnaire whether their 3-year-old had been diagnosed with ASD from age 2.
The study was conducted by the Japan Environment and Children's Study Group at 15 regional centers across Japan.
Overall, 330 children had received an ASD diagnosis at age 3 years, a prevalence of 0.4%. Of these, 251 (76%) were boys, and 79 (24%) were girls. Independent of ASD, the most common response for screen time was less than 1 hour, which was reported by 27,707 mothers. The proportion of children with ASD at age 3 increased as screen time at age 1 increased, the percentages were 5.8%, 22.3%, 30.2%, and 31.7% for children with no screen time, less than 1 hour, 1 to less than 2 hours, and 2 to less than 4 hours, respectively. The percentage of children with ASD diagnoses who had 4 hours or more of daily screen time was 10%.
Logistic regression analysis showed that longer screen time at age 1 year was significantly associated with higher odds of ASD at 3 years in boys, but not in girls. The researchers controlled for variables including maternal maltreatment and children's predisposition to ASD. Among boys, the adjusted odds ratios for screen times of less than 1 hour, 1 hour to less than 2 hours, 2 hours to less than 4 hours, and more than 4 hours.
Screen time at age 3 years was not associated with ASD diagnosis at age 3 years, potentially "because the association with environmental factors on brain development varies with age," the researchers noted.
The study findings were limited by several factors including the reliance on parental reports of screen time and potential for reporting bias, the researchers noted. Other limitations included the possible missed diagnoses of mild ASD cases at 3 years, and the inability to consider variables such as childcare environment, living conditions, diseases, genetics, and disabilities.
However, the results were strengthened by the large study population and examination of screen time in early childhood, they said. More research is needed to examine other factors that contribute to the association between ASD and screen time but given the rapid increase in device use in children, "it is necessary to review its health effects on infants and control excessive screen time."
