Gender difference in the association between adult attention deficit hyperactivity disorder symptoms and morningness–eveningness

Authors


Seog Ju Kim, MD, PhD, Department of Psychiatry, Gachon University of Medicine and Science, 1198, Guwol-dong, Namdong-gu, Incheon 405-760, Korea. Email: psychical@hanmail.net

Abstract

We aimed to investigate the association between attention deficit hyperactivity disorder (ADHD) and morningness–eveningness in adulthood. Subjects without psychiatric comorbidity on the Structured Clinical Interview for DSM-IV Axis I Disorders (n = 344) completed the Morningness–Eveningness Questionnaire (MEQ) and the Adult Self-Report Scale for ADHD. MEQ showed an independent and negative association with ADHD symptoms (P < 0.0001). In male subjects, both inattention (P < 0.0001) and hyperactivity–impulsivity were associated with MEQ (P = 0.01). In female subjects, only inattention was associated with MEQ (P < 0.001). Our findings suggest that eveningness may be strongly associated with inattention of adult ADHD and that it may be associated with hyperactivity–impulsivity of adult ADHD in male subjects only.

RECENTLY, ATTENTION DEFICIT hyperactivity disorder (ADHD) has been regarded as a potentially life-long disorder. Similarly to childhood ADHD, adult ADHD is also associated with sleep disturbances or circadian abnormalities.1,2 Therefore, adult ADHD may also be related to the preference of morning/day activity (i.e. morningness) or evening/night activity (i.e. eveningness), an indicator for circadian rhythm.

A previous study reported the association between eveningness and ADHD in a sample, the majority of whom consisted of female university students.3 However, both morningness–eveningness and ADHD are substantially affected by psychiatric comorbidity, age and gender.4–6 Therefore, these confounders must be regarded as important variables in research concerning adult ADHD or morningness–eveningness. We aimed to investigate the association between ADHD symptoms and eveningness in adults with a broader age range whose psychiatric comorbidity was verified and to explore the gender differences in the association.

METHODS

Subjects

Initially, 393 community-dwelling adults (age range: 19–79 years) were recruited by posters and brochures from the Incheon area, Republic of Korea. The Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-IV) was carried out between psychiatrists and all participants. Among the initial 393 subjects, 49 subjects with Axis I psychiatric disorders were excluded. Finally, 344 subjects (134 male, 210 female, 43.53 ± 14.15 years old) participated in the current study. The study protocol was approved by the institutional review board at Gachon University of Medicine and Science.

Among the 344 subjects, 44 (12.8%) were classified as the potential ADHD group. There was no significant difference in age between the potential ADHD group and the non-ADHD group. Potential ADHD was more commonly found in male subjects (19.71%) than in female subjects (9.52%) (χ2 = 4.43, P = 0.03).

Procedure

The Adult Self-Report Scale v 1.1 (ASRS) from the World Health Organization Composite International Diagnostic Interview was used for screening adult ADHD, as there were no criteria specific for adults in the DSM-IV. The first six items from the original 18 items of the ASRS were used, as these six items are more powerful screening tools than the full scales.7 Four of the six items represent symptoms of inattention, while the other two represent symptoms of impulsivity–hyperactivity. If subjects had four or more symptoms among the six items, they were classified as having potential adult ADHD. The English version of ASRS was translated into Korean and was checked by two board-certificated psychiatrists. The Korean version showed tolerable internal consistency (Cronbach's α = 0.69) and good test–retest reliability (intraclass correlation coefficient = 0.93). The validation process of the Korean version has not been confirmed.

The Korean version of the Horne and Ostberg Morningness–Eveningness Questionnaire (MEQ) was used to measure morningness–eveningness.8 A higher MEQ score means higher morningness and lower eveningness.

Statistical analysis

Differences in the MEQ scores between groups were evaluated using ancova (covariates: age and gender). Multiple regression analysis was also used for evaluating the relationship between the MEQ scores and the number of ADHD symptoms (dependent variable: ADHD symptoms; independent variables: MEQ score, age, and gender). Statistical significance was defined at an alpha of <0.05 and two-tailed.

RESULTS

Among the male subjects, the MEQ scores were significantly lower in the potential ADHD group after controlling for age. After age was controlled for, a lower MEQ score in male subjects significantly predicted inattention, impulsivity–hyperactivity and total ADHD symptoms (Table 1).

Table 1.  MEQ scores and adult ADHD symptoms on ASRS
 Male subjects (n = 134)Female subjects (n = 210)Whole subjects (n = 344)
  • *

    P < 0.05,

  • **

    P < 0.001,

  • ***

    P < 0.0001.

  • After controlling for age.

  • After controlling for age and gender.

  • ADHD, attention deficit hyperactivity disorder; ancova, analysis of covariance; ASRS, Adult Self-Report Scale v 1.1; MEQ, the Horne and Ostberg Morningness–Eveningness Questionnaire.

Differences between potential ADHD and non-ADHD   
 Potential ADHD (n = 44)n = 24n = 20n = 44
 MEQ scores42.38 ± 9.9350.90 ± 12.2446.25 ± 11.72
 Non-ADHD (n = 300)n = 110n = 190n = 300
 MEQ scores52.38 ± 10.4554.30 ± 9.2353.60 ± 9.72
 ancovaF = 22.82***F = 3.36F = 21.94***
Relationship between MEQ scores and ADHD symptoms   
 Inattentionβ = −0.45***β = −0.33**β = −0.34***
 Impulsivity–Hyperactivityβ = −0.27*β = −0.11β = −0.19*
 Total symptomsβ = −0.47***β = −0.28**β = −0.36***

Among the female subjects, the MEQ scores of the potential ADHD group were also lower, but the statistical significance was not reached after controlling for age (P = 0.06). After age was controlled for, a lower MEQ score in female subjects significantly predicted inattention and total ADHD symptoms, but not impulsivity–hyperactivity (Table 1).

In total subjects, the MEQ scores were significantly lower in the potential ADHD group after age and gender were controlled for. After controlling for age and gender, a lower MEQ score significantly predicted inattention, impulsivity–hyperactivity and total ADHD symptoms (Table 1).

DISCUSSION

The current results showed the association between eveningness and adult ADHD. As subjects with other Axis I psychiatric disorders were excluded in the current study, the eveningness–ADHD association seemed to be independent from psychiatric comorbidity. In addition, our results suggest that the eveningness–ADHD association might also be found even in middle or older ages.

One previous study of 205 adults reported that eveningness was related only to inattention, but not to hyperactivity–impulsivity of ADHD.3 Corresponding to this previous study, we found that eveningness was strongly associated with inattention of adult ADHD in both genders. It might be inferred that inattention of ADHD and eveningness might share some neurobiological or genetic characteristics. Otherwise, it is also plausible that eveningness-related sleep disturbances might induce the decline of attention similar to ADHD symptoms.

The most unique finding of the current study was that hyperactivity–impulsivity was associated with eveningness only in male subjects. Although this finding was not in line with the previous study mentioned above, subjects of the previous study were predominantly female (78.6%) or university students (81.5%). The gender differences might be related to a higher proportion of predominantly inattentive type cases in female ADHD relative to male ADHD.6 However, the reason for the gender difference still remains unclear.

In spite of the limitation that the Korean version of the ASRS is not a diagnostically validated tool, but only a screening tool, for adult ADHD, our results suggest a strong association between eveningness and inattention of adult ADHD. In addition, our finding demonstrated a gender difference in the association between eveningness and hyperactivity–impulsivity of adult ADHD.

ACKNOWLEDGMENTS

This study was supported by a grant from the Korea Healthcare technology R&D Project, Ministry for Health, Welfare & Family Affairs, Republic of Korea (A090059).

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