If you ask the experts, they will tell you that approximately 9% of children in the US have the cluster of symptoms defined as ADHD. 5-16% of kids will have what is called "Oppositional Defiant Disorder," where kids deliberately break the rules, are quick to anger, and will often be sensitive and vindictive, among other problems. Perhaps not surprisingly, these disorders overlap, with something like 50% or more of kids with ODD also having symptoms of ADHD. It is also stressful and difficult to be surly and argumentative - 35% will also have a mood disorder, such as a depressive disorder.
I've already blogged quite a bit about the best research on the suspected links between diet and ADHD. Kids diagnosed with ADHD were put on an anti-allergy diet (meat, vegetables, rice, water, pears and, for some, small amounts of wheat, potato, and other fruits), and 60% of them had significant improvement in ADHD and oppositional symptoms, which returned when they were switched back to the "healthy" control diet. But another important behavioral link to ADHD is sleep quality. It is known that kids with ADHD are poor sleepers in general compared to kids without ADHD, but what comes first? Do the brain changes in ADHD screw up sleeping patterns, or do the sleeping pattern problems cause ADHD? It may actually be a two way street for many, but a compelling recent line of research suggests that lack of sleep may be the causative issue for some kids.
First, some definitions. There are basically three kinds of "sleep-disordered breathing" in kids: obstructive sleep apnea (OSA - more common with obesity and allergy where kids get large tonsils and adenoids), upper airway resistance syndrome (UARS - probably also a structural or allergic phenomenon), and primary snoring. There is also the relatively rare central apnea, where kids stop breathing and drop oxygen levels because the brain seems to forget to tell the lungs to work sometimes in sleep (happens with 10% of people on chronic opiate treatment for pain, too! Scary.) The difference between the obstructive and upper airway resistance apneas have to do with differences in how the diaphragm and chest work together to push the air out. In both cases, the oxygen levels in the blood drop due to not getting enough air. Do this all night, every night, and your brain gets to be a bit irritated with you. Brain needs oxygen. However, even kids who snore without dropping oxygen levels (the primary snorers) have more interrupted sleep and problems similar to those kids with OSA and UARS (1).
What kinds of problems? Well, hyperactivity, poor attention, if young, lower scores on IQ tests, defiant behavior, poor grades. Sounding familiar? Interestingly, studies haven't consistently shown a connection between OSA and defiant behavior and low IQ in adults, though there are issues with inattention in adults (2). In a study of kids with OSA who have surgery to remove the big floppy tonsils and adenoids that kept them from breathing properly (3), aggressive, inattentive, and hyperactive behavior significantly decreased following the surgery. That's a pretty telling finding strongly suggesting that poor sleep in kids causes symptoms of ADHD and ODD.
In the German study of 1114 mostly Caucasian kids (1) from a random sample of schoolchildren, 114 ended up being habitual snorers, with most of that number ending up diagnosed with primary snoring, and a smaller number UARS and OSA. It is interesting to me that number is pretty similar to the 9% overall prevalence of ADHD (though not all snorers had ADHD symptoms, and some never-snorers had ADHD symptoms).
In the Cinncinati study of overweight older children and adolescents (2), it was noted that childhood obesity rates in 10-16 year olds have tripled in recent decades, to 16%, and minorities are overrepresented in this group. 13-39% of these obese kids will have sleep disordered breathing (SDB). Among the obese kids without sleep problems, very few made the cut-off in this study for attentional problems, whereas of the kids diagnosed with SDB, 44% of them were defined by parents and 38% defined by teachers as having attentional problems.
To add yet another wrinkle, in a 2008 Yale study, 34 kids age 7-19 with metabolic syndrome and a positive sleep problem questionnaire were recruited to have sleep testing done. 25 of them ended up with sleep-disordered breathing, and those kids had higher sympathetic response (suggesting a raised level of overall stress, which eventually puts one at risk for all those diseases of inflammation, especially depression, anxiety, etc.) and higher leptin levels while insulin resistance was not elevated. This is some evidence that leptin resistance occurs first, prior to insulin resistance, in the pathology of metabolic syndrome. Treatment of the sleep-disordered breathing with a CPAP machine (a contraption that you wear at night to help you breathe better) for three months resulted in a near significant decrease in sympathetic activation, and a significant decrease in leptin levels.
Sadly, of a group of obese kids 4-20 years old, 38.7% of the moderately obese had metabolic syndrome , and 49.7% of the severely obese kids did. Obesity in kids, as well as adults, is associated with hypertension, dyslipidemia, chronic inflammation, increased blood clotting, endothelial dysfunction, and high triglycerides.
The big picture - what is a common solution that would presumably help the inflammatory/allergy and the metabolic syndrome/obesity issues with oppositional behavior and attention in kids all at the same time? Might it be that same old paleolithic-style diet I keep coming back to, along with regular exercise and dedication to proper sleep habits? Killing all birds with one skillfully thrown stone, the evolutionary medicine lifestyle. Again.