ADHD Myths (page 2)
ADHD is caused by too much sugar (or aspartame, or preservatives, etc.) in the diet.
Among the causal myths about ADHD, some have targeted common dietary substances, including sugar, aspartame (an artificial sweetener), various food colorings, and preservatives. However, the role of dietary factors has been investigated for three decades without producing evidence of a relationship. In 1982, at a consensus conference convened by the National Institutes of Health, researchers reviewed over 20 studies and found that no relationships existed between dietary variables and the symptoms of ADHD. Neither those studies nor others conducted since that time have yielded any evidence of a relationship between the consumption of specific substances and the symptoms of ADHD (Hoover & Milich, 1994; Shaywitz et al., 1994; Wolraich et al., 1994; Wolraich, Milich, Stumbo, & Schultz, 1985).
When a complete causal explanation of ADHD is established, it will not be so simple as the effects of ingesting sugar or artificial sweetener. Nor is it likely that it will involve a single cause. Just as a number of causal elements have been found for medical conditions such as heart and bone diseases, scientists believe multiple factors will ultimately be identified as causes of ADHD (LaHoste et al., 1996).
ADHD is caused by poor parenting.
Although some members of the public have stated that poor child-raising practices are responsible for causing ADHD, research has found no evidence to support this myth. However, research has revealed that in a significant number of cases, parents' genetic contributions to their children may "cause" ADHD. One study that investigated the role of genetic inheritance found that when one parent had ADHD, the risk to his or her offspring was 57% (Biederman et al., 1995). Although researchers have not identified a genetic link in all cases of ADHD, they have found that individuals with a family history of the disorder are more likely to have it themselves. This risk may be increased when combined with factors that parents may or may not be able to control, including prenatal health and environmental toxins (Milberger, Biederman, & Faraone, 1994; Sprich-Buckminster, Biederman, Milberger, Faraone, & Lehman, 1993).
Among the studies that have investigated the heritability of ADHD several have found that the parents and siblings of children diagnosed with ADHD are much more likely to have the disorder themselves (Cantwell, 1972; Biederman et al., 1992; Deutsch, Matthysse, Swanson, & Farkas, 1990; Faraone et al., 1993; Hechtman, 1994). Studies of twins have found that if one identical twin has ADHD, the chances have been estimated at 80-90% that the other twin will have it as well (Hechtman, 1994; Levy, Hay, McStephen, Wood, & Waldman, 1997). Findings of the same study indicated that if one non-identical twin has ADHD, there is a 30% chance that the sibling twin will have it as well. Other studies have demonstrated genetic transmission factors in children who have both ADHD and learning disabilities (Faraone et al., 1993; Gilger, Pennington. & DeFries, 1992; Gillis, Gilger, Pennington, & DeFries, 1992; Semrud-Clikeman et al., 1992).
Researchers are currently investigating the relationship of multiple genetic factors to ADHD. In 1995, a dopamine-related gene was linked to novelty-seeking behavior (Cook et a1., 1995; Benjamin et al.,1996; Ebstein et al., 1996). Two years later, researchers confirmed that it is involved in some cases of ADHD (Gill, Daly, Heron, Hawi, & Fitzgerald, 1997; Swanson et al., 1997).
Although a causal link has not been demonstrated between parenting practices and ADHD, this is not necessarily the case for two other conditions that co-occur at a high rate of frequency with ADHD. Studies have indicated that two disorders associated with significantly difficult and negative behaviors, Oppositional Defiant Disorder (ODD) and Conduct Disorder (CD), may in some cases be connected with parents' behavior. The behaviors associated with ODD and CD appear to be precipitated or exacerbated by some parents' communication styles and child-rearing practices (Sprich-Buckminster et al., 1993).
ADHD does not have a physical cause.
Individuals who believe that ADHD has no physical cause and those who believe that it is a cultural invention should review the findings of the past 100 years' worth of research investigating its likely causal factors. The historical highlights from research literature provided earlier in the article give an overview of the progress that scientists have made in linking behavior to the functioning of various brain structures. Although the precise causes of ADHD have yet to be identified, clearly a great deal has been learned about the relationships between such physical structures as genes and the brain and the symptoms of ADHD (LaHoste et al., 1996).
The myth that ADHD has no physical cause may have continued to circulate since the outward manifestations of the disorder reveal very little about the internal workings that are responsible for its symptoms. However, the investigation of physical factors requires that scientists first determine what constitutes normalcy in the brain's structures and functions. In order to accomplish this, researchers are employing a wide range of advanced technology to examine normal brains and those of persons with diagnosed mental disorders. These applications include magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), positron emission tomography (PET), and sophisticated laboratory methodologies.
Some researchers investigating the relationship of brain to ADHD have focused on the structures that appear to support the executive functions. The involvement of the prefrontal cortex (the outer layer of gray matter covering the cerebral hemispheres) in executive functioning has been well established. These functions have been defined as the “abilities to prioritize, organize, and strategize” (Denckla, 1989) and as the “control processes involving inhibition and delay of responding that allow an individual to initiate, sustain, inhibit/stop, and shift” (Denckla, 1996). The executive function deficits in ADHD appear to involve a network linking various structures of the brain that are believed to be responsible for providing positive and negative feedback to various other parts (Alexander, DeLong, & Strick, 1986). Inadequate inhibition of traffic through these circuits is associated with not only ADHD, but also with Tourette's syndrome and obsessive-compulsive disorder (Alexander & Crutcher, 1990; Alexander DeLong, & Strick, 1986). In addition to the prefrontal cortex, research has indicated that the following brain structures are related to the executive function and that disturbances in them may be associated with some of the symptoms of ADHD:
- Basal ganglia: four collections of neurons located deep in the cerebral hemispheres
- Cerebellum: a portion of the brain that interacts with the brain stem in executing voluntary movement
- Thalamus: a part of the brain that receives input from all the senses (except smell), associates and synthesizes it, and relays it to other parts of the brain
Research was conducted to measure a number of regions of the brains of boys with ADHD, using anatomic MRI to see if their brain structures were different from those of normal subjects (Casey et al., 1997; Castellanos et al., 1994; Giedd et al., 1994). The following differences in the brains of subjects with ADHD were documented:
- smaller cerebral volume
- less asymmetry in the caudate
- smaller right globus pallidus
- smaller anterior frontal region
- smaller cerebellum
- a reversal of lateral ventricular asymmetry
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