Une étude révèle une corrélation surprenante entre l'élévation des états et la prévalence du TDAH

Une étude révèle une corrélation surprenante entre l'élévation des états et la prévalence du TDAH

september 8, 2020 0 Door admin

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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 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:


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