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Sub-clinical levels of attention deficit-hyperactivity
disorder are associated with tobacco consumption in male but not in female
Rebecca L. Douglas, Sean P. Barrett*, Neil T. Hanley and Robert O.
* To whom correspondence should be addressed: Sean
P. Barrett,Department of Psychology, McGill University, 1205
Doctor Penfield, Montreal, Quebec Canada, H3A 1B1. Fax: (514)
3984896; Phone: (514) 398-6119;firstname.lastname@example.org
ABSTRACT An abundance of evidence
has demonstrated an association between symptoms of attention
deficit hyperactivity disorder (ADHD) and tobacco consumption.
However, previous research has focused solely on populations
meeting full diagnostic criteria for ADHD, despite evidence
suggesting that symptoms below diagnostic threshold can
be associated with impairment. Furthermore, the role of
gender in the relationship between ADHD symptoms and tobacco
consumption has not been determined. To examine the relationship
between ADHD symptoms, tobacco use, and gender in a non-clinical
population, symptoms of inattention, hyperactivity and
impulsivity were assessed in 230 undergraduate students
(22 male and 45 female smokers, and 66 male and 97 female
nonsmokers). Overall, relative to nonsmokers, the smoking
subjects reported significantly higher levels of inattention
and hyperactivity. In male smokers, both inattentive and
hyperactive/impulsive symptoms were positively associated
with the number of cigarettes smoked daily. This relationship
did not hold for female smokers, for whom no association
was found between symptoms and nicotine consumption. Findings
imply that even sub-clinical levels of inattention and
hyperactivity/impulsivity are related to indices of tobacco
use in males, and support previous research suggesting
that significant gender differences may exist in tobacco
smoking motives. Results also have potential implications
for tobacco cessation programs, which may require more
Attention deficit hyperactivity disorder (ADHD) is a pervasive psychiatric
disorder, characterized by symptoms of inattention and/or hyperactivity-impulsivity.
The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) currently
recognizes three subtypes of ADHD: (i) a hyperactive-impulsive type, characterized
by excessive motor activity and a difficulty in delaying responses, (ii)
an inattentive type, in which individuals display a failure to pay close
attention to detail or to sustain attention, and (iii) a combined type
that includes features of both hyperactivity-impulsivity and inattention
(1). Although traditionally perceived as a form of childhood pathology,
it is now widely recognized that ADHD often persists into adulthood (2-4).
In order for an individual to receive a diagnosis of ADHD, six out of
nine criteria for inattention and/or hyperactivity/impulsivity must be
met (1). Individuals presenting with fewer than six criteria do not receive
a diagnosis of ADHD, regardless of the degree of impairment (1). As no
physiological significance has been attached to the cutoff criteria (5,6),
the diagnostic threshold for ADHD is potentially arbitrary. In fact, problematic
levels of disruptive behavior associated with hyperactivity and impulsivity
seem to occur even when the symptom count does not meet the diagnostic
threshold (7,6), indicating that the impairment associated with the disorder
is not categorical. Although evidence suggests that significant dysfunction
can be associated with sub-threshold levels of ADHD symptomatology (6,7),
little is known about how 'nonclinically significant' levels of hyperactivity
and/or inattention relate to other forms of pathology. Because ADHD has
been associated with a range of substance use problems, such as marijuana,
cocaine, and other stimulant drug use disorders (8), as well as conduct
problems, mood disorders, anxiety disorders, and learning disabilities
(2, 3), it remains possible that the presence of even sub-clinical symptoms
may increase an individual's risk for certain adverse outcomes, including
substance use and other psychiatric disorders.
An abundance of evidence suggests a link between the presence
of ADHD symptoms and tobacco usage. ADHD in childhood has been
associated with significantly younger age of first tobacco use
(9) and younger age
of commencement of daily tobacco consumption (10). In addition,
a greater proportion of adults with ADHD display tobacco dependence
controls (11, 10). The relationship between tobacco consumption
and symptoms of inattention and hyperactivity/impulsivity may
be partially or completely
explained by attempts to self-medicate symptoms of ADHD. Nicotine
has been demonstrated to ameliorate both inattention and hyperactive/impulsive
behavior (12, 13). Nicotine has also been demonstrated to induce
improvements, mostly in attentional areas, in normal nonsmoking
adults as well as those with impairments (13). Even low doses
of nicotine have
been shown to significantly reduce errors of omission on attentional
tasks, without increasing errors of commission, thus indicating
that the effects
are not simply due to increased responding (13). These effects
do not appear to diminish with chronic administration (13). Significant
in memory performance, specifically working memory, have also
been shown with nicotine administration over long periods of
The various effects of nicotine on attention and behaviours related to
hyperactivity/impulsivity may be linked to nicotine's effect on dopamine
transmission. Nicotine indirectly facilitates dopamine transmission, through
stimulation of the nicotinic acetylcholine receptors located on dopamine
containing neurons (14, 15). Studies of smokers have shown that nicotine
seems to inhibit monoamine oxidase-B (MAO-B), thus increasing the availability
of dopamine in the brain by preventing breakdown (11). Nicotine is also
believed to exert its effect on working memory and on regulation of impulsive
behaviors by interacting with the dopaminergic systems and receptors in
the brain (11, 13).
Because ADHD symptoms are thought to result from dopamine dysfunction
particularly in frontal and striatal regions (2), it seems possible that
individuals who display greater inattention or hyperactivity/impulsivity
may use tobacco in an attempt to address these symptoms. Previous research
has in fact suggested that tobacco may be used for self-medication in
clinical ADHD populations (10), and as sub-threshold symptoms of inattention
and hyperactivity/impulsivity also result in impairment (6,7), there may
be motivation for individuals, even in non-clinical populations, to self-medicate.
There is some evidence to suggest that gender differences may exist in
the relationship between smoking and ADHD symptoms. It has been suggested
that females may be less sensitive to nicotine's effects (17); the lower
efficacy of nicotine replacement therapy found among females in smoking
cessation programs suggests a decreased sensitivity in females to the
negative reinforcement effects of nicotine (17). Males also appear to
be more likely to self-administer nicotine (17). The findings of gender
specific nicotine effects raise the possibility of differences in likelihood
to self-medicate ADHD symptoms with tobacco.
To date, research that links tobacco smoking with symptoms of ADHD has
focused on participants whose symptoms meet the full diagnostic criteria
for ADHD. Although such symptoms fall on a continuum (5), with concomitant
dysfunction even at levels below the diagnostic threshold (6,7), the degree
to which subclinical levels of either inattention or hyperactivity/impulsivity
may be related to tobacco smoking behavior is not known. Furthermore,
although there appears to be significant gender differences in the manifestation
of hyperactive/impulsive and inattentive symptoms (16), previous studies
examining the link between ADHD and tobacco smoking have either used male
participants exclusively (9) or have failed to analyze male and female
participants separately (10). Thus, the relationship between inattention
and/or hyperactivity/impulsivity symptoms and tobacco consumption remains
unknown in females.
The purpose of this study was to examine the relationship between inattention,
hyperactivity/ impulsivity, and tobacco consumption in a non-clinical
population, and to determine how this relationship may differ
with respect to gender.
Two hundred forty-four undergraduate university students volunteered
to participate in the study. Potential participants were excluded
on the basis of past or present ADHD or other psychiatric diagnoses,
however the use of illicit drugs was not an exclusion criterion. In total,
participants were eliminated for not meeting the study's inclusion
criteria. Volunteers were approached at various locations at
campus and were asked to complete anonymous questionnaires. The
questionnaire consisted of an eighteen-item checklist for ADHD
symptoms, as defined
by the DSM-IV (1), consisting of nine items each for inattention
and hyperactivity/impulsivity. Because the DSM suggests an assessment
of childhood symptoms in adults
with ADHD (1) a nineteenth item asked participants to rate their
level of childhood hyperactivity. Similar self-report check-lists
used in clinical practice for the assessment of ADHD in adults
(e.g. 18, 19) and this method of ascertaining current and childhood
ADHD is widely considered to be reliable and valid in both clinical
(18, 19) and non-clinical populations (20). Participants were
asked to indicate
the degree to which each item applied to them using visual analogue
scales. Based on their self-reported endorsement of symptoms,
each participant was assigned a total composite ADHD score, as well as
hyperactivity /impulsivity sub-scores, based on DSM-IV ADHD diagnostic
criteria (1). While possible scores ranged from zero to ten on
all item scales, with higher scores reflecting greater symptomatology,
converted to z-scores before calculating composite scores in
order to avoid excessive influence of items with a limited range
of responses. Therefore, means reported for overall symptoms and the two
appear as z-scores. In addition to completing the ADHD self-report
participants also reported on their lifetime use of tobacco.
Participants were classified as current smoker, never smoker,
or former smoker. In
order to control for the potential confounding factor of smoking
cessation, 15 former smokers were eliminated from the analysis.
In addition to reporting
their smoking status, smokers also reported the average number
of cigarettes typically consumed daily. All participants were
blinded to the specific
hypotheses of the study, but the investigators were not.
Pearson bivariate correlations were performed in order to determine the
relationship between measures of tobacco consumption and ADHD symptomatology,
while independent t-tests were performed to examine potential effects
of gender and smoking status.
Symptoms of inattention and hyperactivity or impulsivity were assessed
in a non-clinical sample of 67 smokers (67% female) and 148 nonsmokers
(60% female) with a mean age of 21.57 years (SD = 2.55, range
18 to 30). Males and females did not significantly differ in their current
status (26.8% vs. 33.8% classified as current smokers; 2 (1,
N=215)=1.15, p=.760, NS) , nor did male and female smokers differ in their
number of cigarettes smoked per day (males M = 5.86, SD = 8.27;
females M = 4.46, SD = 7.17; t (65) = .65, p = .479, NS).
The analyses revealed significant differences between smokers
and nonsmokers on the measures of overall symptoms as well
as inattention and hyperactivity/impulsivity separately. Current smokers
overall ADHD symptoms (M = .09, SD = .44) than did nonsmokers
(M = -.07, SD = .37; t (211) = -2.74, p = .007). Smokers rated
higher symptoms of inattention (M = .11 , SD = .51) than nonsmokers
(M = -.08, SD = .49; t (212) = -2.29, p = .023) as well as
having higher hyperactivity/impulsivity (smokers M = .08, SD = .49; nonsmokers
M = -.07,
SD = .45; t (140) = -2.17, p = .031).
Within male and female smokers combined, only symptoms of hyperactivity/impulsivity
were related to level of tobacco consumption (r(67) = .254, p =.038).
However, when analyzed by gender, it was determined that the relationship
found between smoking and level of ADHD symptoms differed between males
and females. While daily consumption was strongly associated with overall
symptoms (r(22) = .595, p = .003), inattention (r(22) = .483, p =.023)
and hyperactivity/impulsivity (r(22) = .554, p =.007) in males, there
were no significant relationships between smoking and ADHD symptoms in
females (ps > .100, NS).
Finally, the relationship between the degree of childhood hyperactivity
and current cigarette consumption was assessed. With male smokers, there
was a modest but non-significant association between childhood hyperactivity
and current daily consumption (r(22) =.391, p = .07), whereas this association
was not observed in female smokers (r(45) =.007, p = .961, NS).
Based on previous findings of increased tobacco use in clinical ADHD
populations (e.g. 9) and the recognition that ADHD symptoms fall on a
continuum (5, 6) with impairment occurring at sub-diagnostic levels (6,7),
it was hypothesized that tobacco use would be positively associated with
inattention and hyperactivity/impulsivity in a non-clinical sample.
Indeed, significant differences in levels of both inattention and hyperactivity/impulsivity
were found between smokers and nonsmokers, with smokers displaying
much greater levels of each sub-score. Amongst smokers, daily consumption
positively associated with both inattention and hyperactivity/impulsivity
in males. Interestingly however, no significant relationships
were found among female participants.
In an attempt to discern the direction of the relationship between
ADHD symptoms and tobacco consumption, temporal order was addressed.
Although not significant, an association was identified between
the reported level
of childhood hyperactivity and current tobacco consumption
in male smokers. No parallel association was found with female smokers.
The relationship between smoking and symptoms of inattention and hyperactivity/impulsivity
found in males may be due to an attempt to self-medicate symptoms of ADHD.
Males with more ADHD symptoms may have higher nicotine consumption due
to nicotine's positive effects on attention and symptoms of hyperactivity/impulsivity
via its indirect effects on the dopaminergic system. The dramatic gender
differences found in the relationships between tobacco consumption and
ADHD symptomatology add a further layer of complexity. One possibility
for these observed differences is that males alone self-medicate with
tobacco. This possibility is supported by the findings that suggest gender
differences in the motivation for tobacco consumption and maintenance
(17). The current findings are consistent with the evidence that females
may be less sensitive to nicotine's effects (16). Given the gender specific
effects of nicotine and the proposed gender differences in smoking motives,
women may be less likely to self-medicate with tobacco for ADHD symptomatology,
as it is the nicotine component in tobacco that is suggested to influence
symptoms of ADHD.
There are several implications for the findings of this study. First,
the finding that smoking is associated with inattention and hyperactivity/impulsivity
even in a non-clinical population supports previous research that has
found functional impairment in those below the diagnostic threshold of
ADHD symptomatology (6,7). Second, there is support for previous research
reporting significant gender differences in tobacco smoking motives. Both
these findings have implications for the prevention and treatment of tobacco
consumption for those with ADHD symptoms. Individual differences, for
example in levels of inattention and hyperactivity/impulsivity, may be
factors that need to be considered in designing programs for both prevention
and treatment of tobacco consumption. If smoking functions to self-medicate
the ADHD symptoms of some individuals, then employing other methods to
medicate or manage these symptoms may facilitate smoking cessation. Furthermore,
cessation programs may need to be tailored by gender in order to target
the appropriate smoking motives. Future research is needed to further
examine this phenomenon of self-medication with tobacco in those with
clinical, as well as non-clinical, ADHD symptomatology, as well as to
examine possible gender differences in tobacco usage and the effects on
symptoms within this population.
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