Previous studies have shown an association between ADHD and mood disorders. People with ADHD often also have asthma and other allergies.
What has not been known until now is how the combination of ADHD and asthma affects the occurrence of mood disorders, specifically depression.
This study was conducted by Mu-Hong Chen, from the Department of Psychiatry at Taipei Veterans General Hospital and the Institute of Hospital and Health Care Administration at National Yang-Ming University in Taipei, Taiwan, and colleagues.
Some studies have found that teenagers with ADHD have a higher risk of developing depression and bipolar disorder. There is some scientific evidence that patients with asthma have a higher risk of mood disorders.
This research team reported that theirs was the first study to look at adolescents with asthma, ADHD or the combination of asthma and ADHD, and to compare these teens to a control group for evaluating risk of developing a depressive disorder over seven years.
Study participants were recruited in 2003 from the National Health Insurance Research Database in Taiwan. The researchers grouped them by diagnosis of asthma, ADHD or both. Diagnoses of other allergic conditions were noted, as was whether the adolescent lived in a rural or urban area. A set of control study subjects was also identified and recruited from the database.
The study participants were followed for seven years to determine if they developed a diagnosis of a depressive disorder.
There were 1,172 participants with ADHD, 487 with asthma, 238 with the combination of asthma and ADHD and 7,552 controls.
Analysis of the characteristics of the teens in the study showed that they lived in rural and urban areas equally.
There was a difference in the presence of allergies in the study patients compared to controls.
Skin inflammation, known as atopic dermatitis, was seen in 2.5 percent of the controls, 7.3 percent of the asthma patients, 6.8 percent of the ADHD patients and 16 percent of the patients with both asthma and ADHD.
Allergic eye inflammation was seen in 12.4 percent of control subjects, 22.8 percent of patients with asthma, 19.3 percent of the ADHD patients and 39.4 percent of the study subjects who had both asthma and ADHD.
Allergic nose inflammation was reported in 21.2 percent of controls, 63.6 percent of patients with asthma, 36.8 percent of ADHD patients and 85.3 percent of participants with both asthma and ADHD.
Patients who had asthma only did not have an increase in depressive disorders in the seven years of this study.
ADHD and the combination of ADHD and asthma greatly increased the risk of developing depressive disorders.
The risk of developing any depressive disorder during the seven years of the study was not significantly elevated in the group of asthma patients. The adolescents with ADHD had a 9.3-fold higher risk and those with asthma and ADHD had a 12.2-fold higher risk of developing a depressive disorder compared to study controls.
When the occurrence of major depression was analyzed in the different study groups, the researchers found an 8.6-fold higher risk in adolescents with ADHD and a 10.2-fold higher risk in subjects with both asthma and ADHD. The risk was not increased in the participants with asthma only.
The biggest difference was seen in bipolar disorder in the adolescents studied. The risk of developing bipolar disorder in the asthma-only group was 1.9-fold higher than the control group and was not a significant increase. The ADHD patients had a 10.4-fold higher risk of developing bipolar disorder in the seven years the study was conducted. Patients with both asthma and ADHD had a 31.2-fold higher risk of developing bipolar disorder, a risk much higher than adding the individual risks the asthma-only patients and ADHD-only patients together.
The researchers concluded that ADHD was a risk factor in adolescents for developing depression later in life and that if the adolescent also had asthma, the risk was increased much more. The greatest risk increase was seen in the risk of developing bipolar disorder among adolescents who had both ADHD and asthma.
“Further studies would be also required to elucidate whether proper treatment of asthma could decrease the long-term risk of mood disorders among ADHD patients," the authors wrote.
Publication of this research appeared in the November issue of the Journal of Affective Disorders.
The research team disclosed no conflicts of interest.
Funding for this study came from a grant from the Taipei Veterans General Hospital.