Prevalence of Attention Deficit Hyperactivity Disorder among Older Adults in Northwestern Iran

Introduction

Attention deficit hyperactivity disorder (ADHD) is one of the most common behavioral and developmental disorders among children and adolescents [1]. A child with ADHD is usually unable to concentrate on any subject and, therefore, experiences difficulties in learning. Some children with ADHD also exhibit increased motor activity. Attention deficit or hyperactivity-impulsivity, or a combination of these cases, is classified into three types depending on the presence of symptoms. Many of such children may also suffer from one or more other behavioral disorders due to comorbid conditions [2, 3]. According to a study conducted in Tabriz, Iran, the prevalence of ADHD was 30.5% among children aged 3-7 years [4] and 9.7% among primary school students based on parent and teacher reports [5].

Initially, ADHD was considered a developmental delay in behavioral control during childhood, usually disappearing by adulthood. However, numerous data indicate that ADHD persists into adulthood [6], and ADHD symptoms persist into adulthood in 60% of cases [3]. The prevalence of self-reported ADHD in Turkey was 10.1%, while the actual prevalence of ADHD among university students was 6.1% [7]. According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV)/Composite International Diagnostic Interview (CIDI), the prevalence of ADHD in adults by published studies averaged 2.8%; it was higher in high-income (3.6%) and upper-middle-income countries (3.0%) than in low/lower-middle-income countries (1.4%) [8].

Based on previous reports in a community sample of Tabriz, the prevalence of ADHD in adults in a sample of residents aged 18 to 45 years was estimated at 3.8% using a psychiatric interview [9]. Another study also showed that the prevalence of ADHD in the general adult population is 2.5% and carries a significant individual burden. The most common comorbid psychopathologies are mood and anxiety disorders, substance abuse disorders, and personality disorders [10].

Based on a review of previous studies, it became clear that this disorder has a great impact on social and inner life. Drug abuse [11], more frequent job changes and multiple marriages [12], unemployment [13], and lower work performance are problems observed in adults with ADHD. Therefore, given the high prevalence of ADHD in childhood and, if untreated, the persistence of symptoms in later life, it is necessary to assess the prevalence of ADHD at other stages of life. Since this disorder is well studied by researchers in adults, it is important to treat it in the older adults as well [6, 14, 15].

When ADHD is combined with other mental disorders in adults and plays a significant role in their disability, it becomes even more important in older adults. Since only a small number of patients with ADHD seek psychiatric treatment, it is suggested that ADHD in adults be studied more seriously in epidemiological and clinical studies [16]. In addition, the symptoms of ADHD in older adults, which may be related to symptoms of mild cognitive impairment and neurodegenerative diseases, should be differentiated for effective treatment of this disease. Accordingly, the present study was conducted to assess the prevalence of ADHD among older adults in Tabriz, northwestern Iran.

Material and Methods

Study design and setting

This cross-sectional study was conducted over 12 months in 2018 to assess the prevalence of ADHD among older adults in the city of Tabriz, northwestern Iran. The statistical population included all older adults 60 years of age and above residing in Tabriz in 2018. Figure 1 depicts the population pyramid of Tabriz, East Azerbaijan. The sample size was determined to be 1,000 individuals based on previous studies [17-19] considering p=0.53, α=0.05, and d=0.1p. Sampling was performed using a two-stage cluster sampling method. First, 150 clusters were randomly selected from the districts of Tabriz, and then 20 households were selected from each cluster. Participant selection was then performed by visiting homes and including older adults aged 60 years or more in the study. Thus, 1,043 individuals were included in our study.

Figure 1. Population pyramid in Tabriz, East Azerbaijan.

Eligibility criteria

Inclusion criteria were informed consent to participate in the study and a minimum age of 60 years. Individuals with severe physical illnesses or serious mental disorders were excluded from the study. Participants could withdraw from any part of the study if they wished.

Participants

A total of 1,043 individuals participated in this study, of whom 454 (43.86%) were men and 581 (56.14%) were women. The mean age of the participants was 68.89 years with a standard deviation of 7.38. The majority of participants had a medium socioeconomic status (64.91%) (Table 1).

Table 1. Demographic characteristics of study participants (n=1,043)

Measurements

Ultra-short versions of the Socioeconomic Status (SES) questionnaire

In this study, a six-item questionnaire was employed to assess socioeconomic status [20]. The questionnaire was developed in Tabriz, Iran, and included questions about education level, car and home ownership, and household income. Scores on the six items were summed. Quartiles were used to classify socioeconomic status (low, medium, partially high, and high). The developers of this questionnaire reported a reliability of 0.65 (measured by Cronbach’s alpha coefficient) and a test-retest reliability of 0.76. The correlation coefficient between the full version and the ultra-short version of the questionnaire was 0.84 [20].

Structured Clinical Interview for DSM-IV (SCID-IV)

SCID is a structured interview that allows for diagnosis based on DSM-IV and is available in two main versions: SCID-I assesses major mental disorders on Axis I, while SCID-II assesses personality disorders on Axis II. SCID is used in psychiatric research more often than any other standard diagnostic interview. Its administration requires clinical evaluation of the interviewee’s responses by the interviewer; therefore, the interviewer must possess clinical knowledge and experience in psychopathology. The main advantage of this type of interview is that it is closer to clinical practice. The Persian version of the SCID, which was used in this study, is a valid instrument for clinical diagnosis and is highly recommended for confirming the diagnosis of mental disorders [21].

ADHD symptom questionnaire based on DSM-5 criteria

The ADHD symptom questionnaire includes all symptoms and diagnostic criteria for ADHD according to DSM-5. It is a fully structured 18-item questionnaire designed for individuals over 18 years of age. According to DSM-5 criteria, if a person has 5 symptoms of attention deficit or 5 symptoms of hyperactivity-impulsivity, or answered ‘yes’ to 10 questions about attention deficit and hyperactivity-impulsivity, then this person is presumed suffering from ADHD during the initial screening. Farokhzadi et al. confirmed the validity and reliability of this questionnaire in Iran [22].

Procedure

Screening for ADHD in adults was conducted by visiting the residence of each participant in the statistical sample and verifying the inclusion criteria by completing an ADHD symptom questionnaire based on DSM-5 criteria by a trained master’s degree holder in clinical psychology. In case of refusal to participate in the study or belonging to an organization providing assistance to people with severe/very severe mental and physical disabilities, the participant was replaced by another. The initial screening was conducted considering the presence of at least 5 symptoms of attention deficit or 5 symptoms of hyperactivity/impulsivity, or a total of 10 symptoms in the questionnaire. SES questionnaire was also completed to assess the socioeconomic status of the participants. At this stage, 283 older adults were selected for clinical psychiatric interviews. Participants with severe mental disorders (e.g., psychotic disorders) or physical illnesses (e.g., Alzheimer’s disease) were excluded during the clinical interview. As a result, 4 patients were excluded. Other diagnostic criteria, including the persistence of symptoms, as well as the presence of symptoms before the age of 12 years, in addition to the analysis of clinical symptoms, were considered in the psychiatric interview. Thus, clinical interviews were conducted with all selected participants based on DSM-5 criteria and using the Wender Utah Rating Scale (WURS), and study subjects with definite ADHD symptoms were diagnosed with adult ADHD.

Statistical analysis           

All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS) version 26. Descriptive statistics, including frequency and percentage, were used to summarize categorical variables such as gender, age groups, and socioeconomic status. The association between demographic variables and the prevalence of ADHD was examined using the chi-squared test and Fisher’s exact test where appropriate. A p-value of less than 0.05 was considered statistically significant.

Results

Table 2 presents data on the prevalence of ADHD among older adults: a total of 41 (3.93%) participants were diagnosed with ADHD based on a psychiatric interview, of which 17 (3.74%) were women and 24 (4.13%) were men. According to the results of the chi-squared test, no statistically significant difference in the prevalence of ADHD was found between men and women (p>0.050).

Table 2. Prevalence of attention deficit hyperactivity disorder among older adults in Tabriz in 2018 (n=1,043)

With respect to socioeconomic status, the prevalence of ADHD was 5.29% among older adults with low socioeconomic status, 3.65% among those with medium socioeconomic status, and 5.08% among those with partially high socioeconomic status. The results of the chi-squared test revealed no significant association between socioeconomic status and ADHD in older adults (p>0.050).

Among the 41 patients with ADHD, 16 (4.65%) were in the age group from 60 to 64 years, 8 (3.29%) were in the age group from 65 to 69 years, 7 (3.45%) were in the age group from 70 to 74 years, 6 (5.17%) were in the age group from 75 to 79 years, and 3 (2.52%) were in the age group of 79 years and older. No statistically significant association was found between age and ADHD (p>0.050) (Table 2).

Discussion

This study was conducted to assess the prevalence of ADHD among people aged 60 years and older in Tabriz, Iran. The results showed that 41 people (3.93%) of older adults were diagnosed with ADHD, with 3.73% being women and 4.13% men.

In the study by Michielsen et al., the prevalence of ADHD symptoms was reported to be 2.8% among older adults, and the prevalence of complete symptoms was 4.2% [23]. The prevalence of symptoms was higher in older adults aged 60-70 years than in those aged 71-90 years. In the study by Kooij et al. in the Netherlands, the prevalence of the disorder ranged from 1% to 2.5% among the population aged 18-75 years [24]. In the study by Guldberg et al., 3.3% of older adults aged 65-80 years retrospectively reported symptoms of ADHD in their childhood [25].

Although previous studies have shown a higher prevalence of ADHD in boys than in girls [1-3, 5, 23], in the present study, the prevalence was almost the same among men and women. According to another study, the prevalence of ADHD was higher in men [13], but the results of our study demonstrated no association between gender and ADHD in older adults. This finding is consistent with previous studies confirming the ineffectiveness of the gender factor in relation to adult ADHD [9, 14].

According to the results of the present study, there are no differences in the prevalence of ADHD among different age groups. This finding is consistent with data from studies among adults [6, 9, 14]. In contrast to our study, Park et al. reported that ADHD symptoms in adults were more prevalent with decreasing age [16, 26]. According to the Australian Personality and Total Health Through Life (PATH) project, the prevalence of ADHD in people aged 68-74 years was lower (2.2%) than in individuals 48-52 years of age (6.6%) [27].

Some researchers believe that the lower life expectancy of patients due to car accidents, drug use, mood disorders, and other health problems is the reason for the lower rates in younger adults. Another reason is the lack of appropriate age-specific diagnostic criteria for this disorder, which complicates differential diagnosis and leads to overlapping symptoms with other diseases. These diseases include dementia, mild cognitive impairment, sleep disorders, medication use, chronic pain, as well as visual and hearing impairments [28-30].

According to other research results, the prevalence of ADHD is not associated with the socioeconomic status of older adults. In this regard, the study by Lee et al. was conducted among American workers aged 18 to 44 years, and it was found that the prevalence of ADHD in them did not differ across different levels of professional skills [9, 16] and education levels [6, 9, 14, 16]. Therefore, a small sample size and its categorization into different gender, age, and socioeconomic groups may reduce the accuracy of findings. Consequently, further research with a larger sample size of people with ADHD is needed to improve the accuracy of identifying the relationships.

Conclusion

Our study has established that the prevalence of adult ADHD among older adults in Tabriz, Iran, was 3.9% (3.7% in females and 4.1% in males). We have found no statistically significant associations of ADHD prevalence in older adults with their age or socioeconomic status.

Limitations and implications for the future

This study has several limitations that should be considered when interpreting its results. First, the cross-sectional design does not allow for the establishment of causal relationships between variables such as socioeconomic status and ADHD symptoms. Second, ADHD symptoms were initially identified using a self-report questionnaire, which may be subject to recall bias or underreporting, especially in older adults. Although a clinical interview was conducted to confirm a diagnosis, the use of retrospective self-reports of symptoms before the age of 12 years may lead to inaccurate recollection. Third, individuals with severe mental or physical disorders were excluded from the study, which may limit the generalizability of the results to a broader population of older adults. Furthermore, despite the use of cluster sampling, the study was conducted in a single urban area (Tabriz), which may limit the external validity of the results to rural or culturally different populations.

Future studies should employ longitudinal design to better understand the temporal relationship between ADHD symptoms in early life and outcomes in later life. Multicenter studies in diverse urban and rural populations will help increase the generalizability of the results. Moreover, the inclusion of objective neuropsychological assessments alongside clinical interviews may improve the accuracy of ADHD diagnosis in older adults. Finally, future studies should explore the potential role of comorbidities and healthcare system factors in the diagnosis and management of ADHD in older adults.

Ethical approval

This study was approved by the Ethics Committee of Tabriz University of Medical Sciences (ID number: 5/4/11677). The regional ethical approval code is TBZMED.REC.1394.909.

Data availability statement

The datasets used or analyzed during this study are available from the corresponding author upon reasonable request.

Conflict of interest

The authors declare that they have no conflicts of interest.

Funding                

This study received no external funding.

Acknowledgements
We are sincerely grateful to all study participants and their families for their input.