What Causes ADHD?
WHAT CAUSES ATTENTION-DEFICIT HYPERACTIVITY DISORDER?
Physical Factors
Advanced imaging techniques have detected differences in the brains
of ADHD children compared to those of non-ADHD children.
Brain Structures. Increasingly, research is suggested that ADHD is a
disorder of the right side of the brain. Specific areas on the right
side may be important in understanding ADHD:
The prefrontal cortex. The prefrontal cortex, which is located in
the front of the brain, is thought to be the brain’s command center;
it regulates the brain’s ability to inhibit responses. A number of
imaging studies has indicated that the prefrontal cortex of the
brain in ADHD may be underactive in comparison with those without
ADHD.
The caudate nucleus and the globus pallidus. The caudate nucleus and
globus pallidus, located near the center of the brain, speed up or
stop orders coming from the prefrontal cortex. Abnormalities in
these areas may impair a person’s ability to brake actions,
resulting in the impulsivity typical of people with ADHD.
Dopamine and Other Brain Chemicals. Important neurotransmitters
(chemical messages in the brain) affect mental and emotional
functioning. Dopamine is under particular scrutiny. Studies have
suggested that dopamine levels are abnormal in the brains of those
with ADHD, with its effects being inhibited in the prefrontal lobes
of the brain, which helps regulate concentration, attention, and
inhibition. Deficiencies in norepinephrine, another brain chemical
that is involved in the fight or flight response, may also be
critical in ADHD. Both of these neurotransmitters are also important
in the “reward” response, in which a person experiences pleasure in
response to certain stimuli (such as food or love). Deficiencies in
these neurotransmitters create an intense need that causes
individuals to seek chemicals, such as nicotine or certain drugs,
that actually attach to receptors for dopamine and that help reduce
these needs.
Nerve Pathways. Another area of interest is a network of nerves
called the basal-ganglia thalamocortical pathways. Abnormalities
along this neural route have been associated with ADHD, Tourettes
syndrome, and obsessive-compulsive disorders, which all share
certain symptoms.
Problems Surrounding Pregnancy. ADHD is often associated with
problem pregnancies and with difficult deliveries. Maternal smoking
during pregnancy is also associated with a higher risk for ADHD. One
study indicated that an increased risk also existed in children of
women who were exposed during pregnancy to environmental toxins,
including dioxins and polychlorinated biphenyls (PCBs).
Genetic Factors
Evidence is increasing that genetic factors play the most important
role in ADHD. The relatives of ADHD children (both boys and girls)
have much higher rates of ADHD, antisocial, mood, anxiety, and
substance abuse disorders than the families of non-ADHD children. In
a twin study, 90% of children with a full diagnosis of ADHD shared
it with their twin. Most likely more than one gene is responsible
for inherited cases. This is not surprising, since there is no
consensus that ADHD is even a single disorder.
Genetic Factors Regulating Dopamine. Researchers are reporting
underlying genetic mechanisms that regulate hyperactivity,
particularly those that affect the neurotransmitter dopamine.
Studies are finding that a variation of a dopamine D4 receptor gene
is common in a high proportion of people with addictions and ADHD,
and it appears to be associated with novelty seeking and
extroversion. Other genes under investigation are those that
regulate dopamine; one is called the dopamine D2 receptor gene. Not
all studies, however, have confirmed the role of dopamine in ADHD.
Genetic Resistance to Thyroid Hormone. About 50% of adults and 70%
of children with a genetic resistance to thyroid hormone, essential
for normal brain development, have ADHD. People who have this
condition appear to have a more severe form of ADHD. The thyroid
disorder is not a common cause of ADHD, however, and only those with
a family history of thyroid disease are at risk.
Dietary Factors
Food and Allergies. Studies on the effect of food and food-additive
allergies are controversial. For example, one reported that 62% of
ADHD children had symptoms provoked by various foods and additives.
Another study indicated, however, that less than 5% of children with
ADHD are affected by food additives and even then, the effect is
very slight. Evidence does suggest, however, that certain children
with behavioral difficulties may be sensitive to certain chemicals
in foods. It should be noted that allergies themselves have recently
been associated with a higher risk for behavioral problems. Children
who respond to allergen-restrictive diets, then, may not have had
true ADHD in the first place. Among the additives and foods that
parents and studies report as culprits in inciting behavioral
changes are the following:
Any artificial colorings (particularly yellow, red, or green).
Other additives.
Milk.
Chocolate.
Eggs.
Wheat.
Aspirin and foods containing salicylates (the compound in aspirin).
They include berries (all), chili powder, apples and cider, cloves,
grapes, oranges, peaches, peppers (bell & chili), plums, prunes, and
tomatoes.
Deficiencies in Zinc and Essential Fatty Acids. Some studies have
found an association between deficiencies in certain fatty acids
(compounds that make up fats and oils) and ADHD. Related to these
findings are studies reporting an association between zinc
deficiencies and ADHD. (Zinc is important in the metabolism of fatty
acids, which in turn affects dopamine, the neurotransmitter likely
to be involved with ADHD.)
Sugar. Although parents often blame sugar for causing children to
become impulsive or hyperactive, a number of studies now strongly
suggest that sugar plays no role in hyperactivity. One study
reported, in fact, that ADHD children had fewer problems after a
high-carbohydrate breakfast than after a high-protein one. Another
reported that children actually moved more slowly after a high-sugar
meal, suggesting the carbohydrates may have a sedative effect.
Infant Malnutrition. Even if they receive enough food later on,
children who suffer from malnutrition as infants may develop
behavior problems, the most prevalent being attention-deficit
disorder.
Treatment
Psychostimulant drugs combined with counseling best control
symptoms. Used alone, psychostimulants have been effective
predominantly with less impulsive ADD children and with children
with primary inattention who have stable home environments. ADD
children with poor impulse control often are less helped by
treatment than are children with primary inattention.
Elimination diets, megavitamin treatments, use of antioxidants or
other compounds, and nutritional and biochemical interventions (eg,
the administration of neurochemicals) have had the least effect. The
value of biofeedback is unsubstantiated. Most studies have found
minimal change in behavior and no sustained benefit.
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