This study examined the associations between asthma and suicidal ideation with and without attempts in adults 18 years and older in the United States. To our knowledge, this is the first study to examine these relationships using a nationally representative sample of adults. The results are consistent with and extend previous literature in this area. First, the results showed a significant link between asthma and suicidal ideation with attempts but not suicidal ideation without attempts. Second, the data failed to support the idea that common sociodemographic factors explained these links. Third, although concurrent mental disorders, smoking, and nicotine dependence accounted for some of the association between asthma and suicidal ideation with attempts, an independent and statistically significant association remained even after controlling for these factors.
These findings are consistent with the general suicide literature and those who have found links between respiratory diseases, including but not specific to asthma, and suicidal behavior among adults in the United States using community-based samples5
and clinical samples.19
For example, the higher rates of suicidal ideation without and with attempts observed in women vs men are likely related to reports that women are more likely to use self-poisoning and overdose methods, whereas men tend to use more irreversible suicide attempt methods.22
The results contribute to our knowledge of the asthma-suicidality link by providing the first available information, to our knowledge, that asthma is associated with suicidal ideation with attempts but does not seem to be linked with suicidal ideation without attempts, as reported in previous studies5,8,20
on suicidal ideation and suicide attempts. The reason for what seems to be discrepant results, relative to suicidal ideation without attempts, is possibly because of differences in the data sources used and difference in the categorization of the outcome. Previous studies have not examined asthma and suicidal ideation with and without attempts using a nationally representative sample, as done in the present study, and, therefore, the findings might not necessarily be discrepant. Also, to the degree that representative samples have examined the link between asthma and suicidal ideation with and without attempts, they often failed to examine distinct suicidal ideation groups by the removal of individuals with a suicide attempt to create groups with increasing severity. This suggests that asthma may be associated with the more severe form of suicidal behavior (ie, suicide attempts) but not with the milder forms of suicidal thoughts without attempts. Researchers8
have speculated that the relationship between asthma and suicidal behaviors is possibly because of ensuing mood and anxiety that results from disability and discomfort associated with asthma, which can be a lifelong disease. Individuals might have frequent thoughts of death with increasing severity solely because they have a potentially life-threatening illness. If this holds true, significant associations between asthma and suicidal ideation with and without attempts should be observed in the present study, as reported by Goodwin and Eaton5
in their follow-up study using data from the Epidemiological Catchment Area study. These findings partially supported this hypothesis by observing a statistically significant association between asthma and suicidal ideation with attempts. Crandall and colleagues19
did not find a statistically significant risk for suicide in their follow-up study of individuals with a history of asthma who presented to the emergency department with suicidal behavior. However, the study was based on nonconcurrent emergency department visits in a single urban city, which limited the generalizability of the results.19
Future studies on this issue can help to enhance our understanding of the mechanism by which asthma is associated with suicidal ideation with attempts but not suicidal ideation without attempts, as observed in the present study; suicidal ideation with and without attempts, as observed in our ad hoc analyses; and suicidal ideation, suicide attempt, and suicide, as reported by Goodwin and Eaton5
; but not with suicide, as observed by Crandall and colleagues.19
The results provided new evidence suggesting that the link between asthma and suicidal behavior is not because of common sociodemographic characteristics. Asthma and depression, the strongest risk factor for a suicide attempt, are both associated with common demographic characteristics, especially in childhood-onset asthma, such as racial minority status, lower household income, and urban residence. As such, it is conceivable that these factors were responsible for this observed association. Our results showed that although common demographics seem to be responsible for some of the strength of this link, the relationship persists even after adjustment.
To the best of our knowledge, these results are the first to investigate the potential role of cigarette use and nicotine dependence in the association between asthma and suicidal behavior, which is important to examine because cigarette use and nicotine dependence have been linked with both asthma11–13
and suicidal behavior.10
It is plausible that smoking was responsible for the observed association between asthma and suicidal ideation with attempts. The 16% change in the association between asthma and suicidal ideation with attempts on adjustment for smoking and nicotine dependence indicated that some of the observed risk can be explained by the independent links between smoking and asthma and between smoking and suicidal ideation with attempts, as proposed. Because the association between asthma and suicidal ideation with attempts remained after adjustment for these factors, the role of other factors is suggested. The 18% decrease in the association between asthma and suicidal ideation with attempts on control for depression, anxiety, and alcohol dependence or abuse indicated that some of the observed risk was because of the difference between asthmatic and nonasthmatic patients in terms of these factors and the independent link between these factors and suicide attempt. A statistically significant association still remained, indicating the role of other factors not examined herein. Adjustment for depression, panic, alcohol dependence or abuse, smoking, and demographic characteristics did not fully explain the association between asthma and suicidal ideation with attempts (as indicated by the remaining statistical significance of asthma), thereby suggesting other mechanisms at work.
Future studies need to examine various other common risk factors to enhance understanding of the mechanism underlying the link between asthma and suicidal behaviors. Prospective studies7,13
beginning early in life (given the onset of many cases of asthma in early childhood) would be useful in examining this association throughout development and in exploring the potential role of other family, genetic, and environmental factors. For instance, it has been suggested that the link between asthma and mental disorders, such as suicide attempt, could be due to early life exposure to risk factors that tend to co-occur, such as depression and nicotine dependence,23
which may also co-occur among parents, both prenatally24
and postnatally. Specifically, it may be that individuals with a parental history of depression, anxiety, and/or suicidal behavior also have a parental history of cigarette smoking and nicotine dependence, which heightens the offspring’s risk for both suicidal behaviors and asthma later in life. This mechanism could not be investigated herein given the use of cross-sectional data, which also limited our ability to elucidate the directionality of the relationship between asthma and suicidal ideation with and without attempts.
In interpreting the results, one needs to bear in mind that information on study variables was self-reported. Asthma status was self-reported, with no validation by review of hospital or physician records or objective respiratory measures, which could affect the validity of the results. Therefore, one needs to think about whether the study measure accurately classified asthmatic patients vs nonasthmatic patients. However, we can have confidence in the results obtained because the lack of objective validation of asthma status would affect both the suicide attempters and nonattempters equally, which would lead to an underestimate of the true risk. Another issue of concern is that information on asthma was collected in part 2 of the NCS-R study, which was based on responses in part 1 and specifically on those meeting the lifetime criteria for a part 1 disorder and a probability sample of other respondents who did not. As such, there was an oversampling of individuals with part 1 disorders, which might account for the lack of statistically significant association between asthma and suicidal ideation without attempts. The NCS-R excluded individuals who died by suicide, which prevented the ascertainment of whether the observed effects were a result of asthmatic patients being more likely to attempt or use less severe methods compared with nonasthmatic patients, who might be using more lethal methods, leading to their death.
Lack of information on the recency of asthma symptoms limits our ability to determine the direction of causality. Even if the onset of asthma occurred before the onset of suicidal ideation or attempt, lack of timing information prevents us from determining if other intermediate factors not examined herein could account for the relationship observed. It is, therefore, imperative to conduct studies with longitudinal data, preferably using nationally representative samples and including information on the mechanisms of injury, onset and recency of asthma, suicidal ideation, and suicide attempts to disentangle these relationships.