Study finds surprising correlation between states’ elevation and ADHD prevalence

Who would have thought that chil­dren liv­ing at high­er alti­tudes have low­er risk of devel­op­ing ADHD than peers at low­er ele­va­tion lev­els? 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 Study:

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.

Results:

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:

• A brief sleep inter­ven­tion can bring mea­sur­able and sus­tained ben­e­fits to chil­dren with ADHD
• 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”
• What are cog­ni­tive abil­i­ties and how to boost them?