All-cause mortality is significantly higher for individuals with autism spectrum disorder or attention-deficit/hyperactivity disorder than for the general population, based on data from more than 600,000 individuals.
Studies of individuals with mental disorders have suggested an increased mortality risk, compared with the general population, but similar studies of individuals with autism spectrum disorder (ASD) or ADHD have yielded inconsistent results, Ferrán Catalá-López, PhD, of the Institute of Health Carlos III, Madrid, and colleagues wrote.
In a systematic review and meta-analysis published in JAMA Pediatrics, the researchers examined 27 studies including 642,260 individuals; 154,238 with ASD and 396,488 with ADHD. The studies were published up to April 1, 2021, and included deaths from natural causes (such as respiratory illness or cancer) and unnatural (external) causes, such as accident, injury, or poisoning. The proportion of females in the studies ranged from 14% to 100%; the follow-up ranged from 3 to 33 years; and three studies included first-degree relatives.
Overall, all-cause mortality was significantly higher among individuals with ASD (rate ratio, 2.37) and ADHD (RR, 2.13), compared with the general population. Among individuals with ASD, deaths from natural causes and unnatural causes were significantly increased, compared with the general population (RR, 3.80 and RR, 2.50, respectively). Among individuals with ADHD, deaths from natural causes were not significantly increased (RR, 1.62), but deaths from unnatural causes were significantly increased, compared with the general population (RR, 2.81).
Potential mechanisms to explain the excess mortality among individuals with ASD and ADHD include health determinants and biological pathways, but the complex nature of the associations make the establishment of causality a challenge, the researchers wrote in their discussion of the findings. In general, “severe mental and behavioral disorders appear to be associated with reduced life expectancy, both in terms of mortality from external causes and mortality from other medical conditions or diseases.” With regard to ASD/ADHD in particular, these individuals often experience emotional and social problems as they enter adulthood. “Behaviors such as impulsivity and/or inattention can be contributing factors for injuries and unintentional incidents in children with ASD/ADHD,” they added.
The study findings were limited by several factors including the possible omission of studies and the use of study-level data rather than individual participant data, as well as the limitation of electronic health records, the researchers noted. Also, the studies were mostly conducted in Western countries and the results may not be generalizable to other countries.
Although ASD and ADHD were associated with a significant increased risk of all-cause mortality, “the results should be interpreted with caution because there was evidence of heterogeneity between study estimates of the mortality risks,” the researchers said. However, the results were strengthened by the large study sample, and offer a comprehensive look at the evidence supporting increased mortality risk among individuals with ASD or ADHD, and highlight the need to identify modifiable risk factors.
“Understanding the mechanisms of these associations may lead to targeted strategies to prevent avoidable deaths in high-risk groups of children and young people as an approach to improve public health,” they said.