I recently reported on an intrigu­ing study exam­in­ing the impact of an herbal treat­ment for youth with ADHD. Results from this randomized-controlled trial were quite promis­ing and con­sis­tent with the idea that some indi­vid­u­als with ADHD have defi­cien­cies in essen­tial nutri­ents that com­pro­mise healthy brain devel­op­ment and result in ADHD symp­toms. This idea has sparked the long-standing debate about whether dietary fac­tors play an impor­tant role in the devel­op­ment of ADHD, at least for some chil­dren, and led to many stud­ies of this issue.
Although results of these stud­ies elude any sim­ple con­clu­sions, dietary fac­tors do appear to con­tribute to ADHD symp­toms in some individuals.

Some have argued that research on the rela­tion­ship between diet and ADHD is more impor­tant than ever because the diets of chil­dren in West­ern coun­tries have shown steady increases in the amounts of heav­ily processed foods rich in sat­u­rated fats, salt, and sug­ars accom­pa­nied by decreases in omega-3 fatty acids, fiber, and folate. Is it pos­si­ble that such ‘West­ern’ style diets are asso­ci­ated with an increased risk of ADHD, and per­haps a con­tribut­ing fac­tor to the high preva­lence of the disorder?

This impor­tant ques­tion was exam­ined in a study pub­lished recently online in the Jour­nal of Atten­tion Dis­or­ders [Howard et. al. (2010). ADHD is asso­ci­ated with a “West­ern” dietary pat­tern in ado­les­cents. Jour­nal of Atten­tion Dis­or­ders]. Par­tic­i­pants were 1172 14 year-old Aus­tralian ado­les­cents and their par­ents who had been recruited into the study and fol­lowed since the moth­ers were between 16 and 20 weeks preg­nant. The data col­lected in this study was part of a large-scale lon­gi­tu­di­nal inves­ti­ga­tion focused on a vari­ety of issues related to under­stand­ing healthy and mal­adap­tive development.

When youth were 14, par­ents were asked whether their child had ever been diag­nosed with ADHD by a qual­i­fied health pro­fes­sional. One hun­dred and fif­teen — nearly 10% — had been diag­nosed, includ­ing 91 boys and 24 girls. These diag­noses were con­firmed by review­ing children’s med­ical records. Pri­mary care­givers also com­pleted the Food Fre­quency Ques­tion­naire (FFQ) in which they rated the typ­i­cal intake by their child of over 200 dif­fer­ent foods from nearly 40 dif­fer­ent food groups.

Based on responses to the FFQ, 2 major dietary pat­terns were identified.

• The ‘West­ern’ pat­tern was pos­i­tively asso­ci­ated with higher intakes of total fat, sat­u­rated fat, refined sug­ars, and sodium. Spe­cific food types promi­nent in the West­ern diet included ‘take­away’ foods (I believe this refers to ‘fast’ food’) red meat, processed meats, soft drinks, full fat dairy prod­ucts, soft drinks, sug­ary foods, and fried foods.
• The ‘Healthy’ pat­tern (these labels were assigned by the inves­ti­ga­tors) was pos­i­tively asso­ci­ated with omega-3 fatty acids, fiber, and folate. Promi­nent foods in the healthy diet included all types of veg­eta­bles, fresh fruit, whole grains, legumes, and fish.

Ado­les­cents received scores on both diet pat­terns based on par­ents’ responses about their typ­i­cal food intake. Those above the mean were clas­si­fied as ‘high’ for that pat­tern and those below the mean were clas­si­fied as ‘low’. Thus, each ado­les­cent was placed in a high or low group for both the West­erns style and Healthy diets. By clas­si­fy­ing par­tic­i­pants in this way, the researchers could exam­ine whether being high vs. low for a West­ern diet and a Healthy diet was asso­ci­ated with an increased like­li­hood of being diag­nosed with ADHD.

Because many fac­tors besides diet may increase risk of ADHD, the researchers mea­sured a num­ber of other vari­ables that could poten­tially con­found the results. These included mater­nal age at con­cep­tion, mater­nal edu­ca­tion, mater­nal smok­ing dur­ing preg­nancy, pres­ence of bio­log­i­cal father in the home dur­ing preg­nancy, fam­ily income dur­ing preg­nancy, and the num­ber of stress­ful life events expe­ri­enced by the mother dur­ing preg­nancy. In addi­tion, data was col­lected on ado­les­cents’ typ­i­cal weekly level of phys­i­cal activ­ity and the num­ber of hours they spent each day watch­ing tele­vi­sion, play­ing video games, or using the computer.

- Results -
After con­trol­ling for all the other vari­ables noted above, ado­les­cents in the ‘high’ group for the West­ern dietary pat­tern were more than twice as likely as those in the ‘low’ group to have been diag­nosed with ADHD.
These results were con­sis­tent for boys and girls. A high score for the Healthy dietary pat­tern, how­ever, was not asso­ci­ated with reduced risk of hav­ing a diagnosis.

When the authors looked at spe­cific food groups, high con­sump­tion of fast food, red meat, processed meats, and high-fat dairy prod­ucts, potato chips, and soft drinks were all asso­ci­ated with increased risk of an ADHD diagnosis.

Increased like­li­hood of an ADHD diag­no­sis was also related to moth­ers hav­ing expe­ri­enced mul­ti­ple stress­ful events dur­ing preg­nancy. The only vari­able asso­ci­ated with lower odds of diag­no­sis was phys­i­cal activ­ity, as youth who exer­cised at least 2 hours per week out­side of school were less likely than oth­ers to be diagnosed.

- Sum­mary and Impli­ca­tions -
Results from this study based on a large com­mu­nity sam­ple of youth clearly indi­cate that a Western-style dietary pat­tern is asso­ci­ated with greater odds of hav­ing ADHD. This was true for both boys and girls. The Western-style diet iden­ti­fied in this study was one that was high in total fat, sat­u­rated fats, refined sug­ars, and sodium.

One pos­si­ble inter­pre­ta­tion of these find­ings is that diets high in these food ele­ments play a direct causal role in the devel­op­ment of ADHD. How­ever, there was no evi­dence that adher­ing to a healthy diet, i.e., one high in veg­eta­bles, fresh fruit, whole grains, and fish, reduced the odds of being diag­nosed. Thus, while West­ern style diets may increase risk for ADHD, the find­ings do not sup­port the notion that adher­ing to a health­ier diet reduces such risk. This does not mean that the healthy dietary pat­tern may not have had other ben­e­fits, but only that it did not alter the risk for ADHD beyond what could be explained by being high vs. low for the Western-style pattern.

While it is tempt­ing to con­clude that the West­ern dietary pat­tern directly con­tributed to the devel­op­ment of ADHD in some youth, the authors are care­ful to note that the design of their study does not allow causal con­clu­sions to be made. For exam­ple, although the con­sump­tion of a more ‘West­ern’ style diet may have “…pro­moted the expres­sion of atten­tion deficits” it is also pos­si­ble that “…diag­nosed atten­tion deficits led to poorer food choices and a more ‘West­ern’ style diet.” For exam­ple, the authors sug­gest that their results “…could be explained by the ten­dency for ado­les­cents expe­ri­enc­ing emo­tional dis­tress to crave fat-rich snack foods as a self-soothing strat­egy.” It is also worth
not­ing that this study did not exam­ine whether dietary changes can reduce ADHD symp­toms and that the find­ings should not be inter­preted in that way.

While no sin­gle study can fully answer com­pli­cated ques­tions per­tain­ing to the role of diet and nutri­tional fac­tors in the eti­ol­ogy of ADHD, this research clearly high­lights that a Western-style dietary pat­tern is asso­ci­ated with increased odds of hav­ing an ADHD diag­no­sis. This sug­gests, but does not prove, that dietary pat­terns may be impli­cated in the devel­op­ment of ADHD, and high­lights the need for addi­tional study so that a more defin­i­tive under­stand­ing of this impor­tant issue can be obtained.

These find­ings also pro­vide an reminder that although risk for ADHD has been strongly linked to genetic fac­tors, it is impor­tant to con­tinue the explo­ration of other fac­tors that may increase risk. Such explo­ration should ulti­mately lead to a richer under­stand­ing of the dis­or­der and how it devel­ops, and hope­fully to the devel­op­ment of more effec­tive treatments.

– Dr. David Rabiner is a child clin­i­cal psy­chol­o­gist and Direc­tor of Under­grad­u­ate Stud­ies in the Depart­ment of Psy­chol­ogy and Neu­ro­science at Duke Uni­ver­sity. His research focuses on var­i­ous issues related to ADHD, the impact of atten­tion prob­lems on aca­d­e­mic achieve­ment, and atten­tion train­ing. He also pub­lishes Atten­tion Research Update, a com­pli­men­tary online newslet­ter that helps par­ents, pro­fes­sion­als, and edu­ca­tors keep up with the lat­est research on ADHD.

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