In last month's issue of Attention Research Update - www.helpforadd.com/2010/august.htm - I 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.  The 'Healthy' pattern (these labels were assigned by the investigators) was positively associated with omega-3 fatty acids, fiber, and folate.  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.  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.