A new study draws links between attention deficit hyperactivity disorder, or ADHD, and oxygen deprivation early on in life.
Earlier studies with animal models have hinted at a connection between lack of oxygen in the womb or during birth and ADHD, but a new study published Monday in the journal Pediatrics takes one of the broadest looks at the connection in humans, using the vast trove of electronic medical records in the Kaiser Permanente Southern California health system.
A team of researchers led by KPSC epidemiologist Darios Getahun started out by combing through medical records for more than 300,000 children between five and 11 years old who were born and raised in the KPSC system between 1995 and 2010.
Getahun and his team identified 13,613 cases of children with ADHD by looking for individuals with a clinical diagnosis of the condition and who had received at least two prescriptions for an ADHD medication. In general, children with ADHD were more likely to be male, and either white or African-American, than children without an ADHD diagnosis.
The scientists matched each ADHD case to five controls, for a total of nearly 82,000 study subjects. Among the subjects, they found that some prenatal exposure to a situation that deprived the brain of oxygen was associated with a 16 percent greater risk of developing ADHD.
Certain conditions carried even greater risks. For birth asphyxia, when a baby is deprived of oxygen right before, during or just after birth, the risk of developing ADHD was 26 percent. For babies exposed to preeclampsia, when the mother has high blood pressure during pregnancy, the risk was 34 percent. And for neonatal respiratory distress syndrome, a condition often seen in premature infants with underdeveloped lungs, the risk for ADHD later in life was 47 percent, the researchers found.
The link between oxygen deprivation and ADHD was strongest in preterm births, regardless of how early or late the child was delivered, and other risk factors.
“This suggests that events in pregnancy contribute to ... this condition over and above the well-known familial/genetic influences,” the researchers wrote.
It is still not precisely clear how oxygen deprivation would cause ADHD. But lack of oxygen is known to affect key parts of a baby's developing brain, including the substantia nigra, an area tied to reward and addiction, and other parts of the frontal lobe and cerebrum.
While the study does not definitively provide evidence that oxygen deprivation actually causes ADHD, the findings are still very clinically valuable, according to Getahun. Physicians can educate mothers on potential risk factors -- for instance, a very high body-mass index during pregnancy raises the risk for preeclampsia -- and identify at-risk newborns who could be watched and treated early on if they start to show signs of ADHD.
In future studies, Getahun says he and his colleagues are interested in seeing if oxygen deprivation is linked to a greater risk for autism spectrum disorders.
SOURCE: Getahun et al. “In Utero Exposure to Ischemic-Hypoxic Conditions and Attention-Deficit/Hyperactivity Disorder.” Pediatrics published online 10 December 2012.