For the first time, researchers have found a link between living at higher altitudes in the U.S. and lower rates of attention-deficit hyperactivity disorder (ADHD). The finding points to the possibility of altitude-related approaches to treating the disorder.
Publishing their findings March 25th in Journal of Attention Disorders, the research team looked at the relationship between rates of ADHD in the U.S. population and the average altitude of U.S. states. Led by Rebekah Huber, M.A., of the University of Utah and Veterans Affairs Medical Center, the team included two NARSAD-funded researchers: Perry F. Renshaw, M.D., Ph.D., a Scientific Council member who was a 1993 and 1996 Young Investigator grantee and a 2000 Independent Investigator grantee; and Douglas G. Kondo, M.D., a 2009 Young Investigator grantee.
Looking at population survey data from 2007 and 2010 and controlling for other ADHD risk factors, the researchers found that in both years, statewide ADHD rates decreased by 0.001 percent for each one-foot increase in a state’s average altitude. Looking at altitude alone, therefore, one would expect a 6.3 percent lower rate of ADHD in Colorado (average altitude of 6,800 feet), than in Connecticut (average altitude of 500 feet). Since these figures relate to rates of ADHD’s occurrence, the impact of the reduction can be dramatic. For instance, in Rhode Island, with an average elevation of 210 feet, 10.3 percent of children are predicted to have an ADHD diagnosis. In Utah, with an average elevation of 6,364 feet, the predicted rate is only 5.3 percent. Among an equal number of children in each state, then, nearly twice as many are expected to have ADHD in Rhode Island.
ADHD is associated with unusually low levels of the neurotransmitter dopamine. Important for motor, motivational, and reward processes in the brain, dopamine works as a chemical signal in the brain in the presence of oxygen. Because oxygen is rarer at higher altitudes, the researchers suggest that levels of dopamine production corresponding with high elevation may help protect children against developing ADHD.
It is also possible, the researchers say, that regional differences in ADHD rates are actually driven by the intensity of sunlight hitting the higher elevated states. Previous research has suggested that sun exposure may regulate ADHD-associated disruptions to the internal clocks that set our sleep schedules.
The researchers caution that more work is needed to support higher altitude as a possible protective factor against ADHD. Population-based studies of ADHD have varied in their findings, suggesting a variety of risk factors including gender, low birth weight (found to be a risk factor in this study), complications of pregnancy, and prenatal exposure to drugs and alcohol. Such variation suggests the factors that produce ADHD are complicated and may overlap.
If more evidence suggests that higher altitudes help reduce rates of ADHD, that would highlight the potential for environment-based treatments for the disorder. Currently, ADHD in the U.S. is largely treated with stimulant medications that target dopamine levels in the brain and can have side effects such as slowed growth, anxiety, aggression, and insomnia.