Une étude révèle une corrélation surprenante entre l'élévation des états et la prévalence du TDAHseptember 8, 2020
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Who would have thought that children living at higher altitudes are at increased risk for the development of ADHD? As the research described below suggests, however, this may be the case.
The impetus for this study is the well-documented regional variation in the prevalence of ADHD in youth. For example, national data for the years 2007–2009 indicate that ADHD prevalence rates were approximately 10% in the south and midwest but only 5% in the western US. How can such substantial regional variation be explained?
The authors of a recently published study, Association between altitude and regional variation of ADHD in youth, suggest that living at high elevation reduces ADHD risk because diminished oxygen levels results in mild hypobaric hypoxia, i.e., less oxygen reaching the brain, which, in turn, stimulates the production of dopamine. This hypothesis is plausible because youth with ADHD show decreased dopamine activity relative to other youth, and stimulant medications used to treat ADHD increase brain dopamine activity. Thus, if ADHD is associated with reduced dopamine activity, and living at high elevation ‘naturally’ increases brain dopamine levels, perhaps ADHD would be less common among youth living at higher elevations.
The authors examined the association between ADHD prevalence and altitude in 2 nationally representative data sets that include tens of thousands of children; one data set was from 2007 and the second from 2010. The data sets include ADHD diagnostic information so that the prevalence of ADHD in all 50 states could be calculated. The average altitude for each state was calculated using data obtained from NASA.
If living at high elevation protected against the development of ADHD, then ADHD rates should be lower in states with higher average elevation compared to states at lower average elevation , i.e., there would be a negative correlation between states’ ADHD prevalence rate and average elevation.
This negative correlation is exactly what was found. In one sample, the correlation between average state elevation and ADHD prevalence was ‑0.53; in the second sample, the correlation was ‑0.54. These results are remarkably consistent and the magnitude of the association is impressive.
In a more fine-grained analysis, the researchers reexamined the link between elevation and ADHD prevalence after controlling for other variables related to ADHD prevalence across states. These included the percent of youth in each state from different racial/ethnic groups, the percent of low birth rate babies, the percent uninsured, the percent living in a two-parent household, and the percent ever diagnosed with depression and anxiety.
After controlling for these factors, mean state elevation remained a significant predictor of ADHD prevalence rate. Specifically, results indicated that for each additional foot in altitude, ADHD prevalence decreased by an average of 0.001%. While .001% is small, the average altitude rate across states is large, ranging from 60 feet above sea level in Delaware to 6700 feet above sea level in Washington. Based on study results, that would lead to a predicted ADHD prevalence rate in Delaware that is 6.6% higher than for Washington, a non-trivial difference.
Summary and implications:
Because this is a correlational study, one cannot conclude with certainty that variations in elevation play a causal role in the development of ADHD. However, in 2 large and nationally representative data sets, a clear and consistent association between altitude and ADHD prevalence was evident. This association remained after controlling for multiple other factors linked to variation in state-wide prevalence of ADHD and may help explain the geographic variation in ADHD prevalence that has been reported. While this demonstrated link between ADHD risk and altitude is surprising, there is also a plausible theoretical mechanism, i.e., living at higher altitude promotes increases in dopamine activity, that may explain it.
This study adds to other work on how natural factors may play a role in the development of ADHD. For instance, several years ago I reviewed a study in which a link between ADHD and exposure to sunlight was found, and exposure to natural outdoor environments has also reported to reduce ADHD symptoms.
Results such as these are surprising and interesting, and highlight the complexity of factors that may be involved in the development and expression of ADHD symptoms.
Several aspects of the current work are important to keep in mind. First, the results highlight a potential linkage between altitude and ADHD at the population level; while interesting to say the least, one can’t conclude from population-level data that living at lower altitude causes the development of ADHD for any individual child. Instead, variations in altitude may be one factor among many that modifies the risk of ADHD and additional work is needed both to replicate the current findings and to better understand the mechanism by which altitude may modify ADHD risk.
Second, it is difficult to know what the practical implications of these findings may be. The authors speculate that conducting summer camps for children with ADHD at high altitudes may help alleviate symptoms. They also suggest that spending time in devices that mimic high altitudes by creating a hypobaric environment — and which have been shown to be safe and effective in the training of endurance athletes — might be helpful for youth with ADHD. Theoretically, this could be an alternative to stimulant drugs for increasing dopaminergic activity. This may be an interesting approach to test, although even if benefits were found, one wonders what the duration would be.
Based on these findings alone, it would certainly be premature to suggest that moving to a high altitude state would improve a child’s ADHD symptoms. However, the findings highlight the value of keeping an open mind in efforts to understand the development of ADHD and the role natural environments may play in potentially alleviating it. Also highlighted is the value of future research into the biological mechanism that is affected by altitude for individuals with ADHD.
– Dr. David Rabiner is a child clinical psychologist and Director of Undergraduate Studies in the Department of Psychology and Neuroscience at Duke University. He publishes the Attention Research Update, an online newsletter that helps parents, professionals, and educators keep up with the latest research on ADHD.
The Study in Context:
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- Study finds combined pharma non-pharma treatment most beneficial to help youth with ADHD address long-term academic difficulties
- Having ADHD costs $1.1 million in lower lifetime earnings, even when “treated”
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