American Journal of Epidemiology Advance Access originally published online on July 14, 2006
American Journal of Epidemiology 2006 164(4):399-400; doi:10.1093/aje/kwj228
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Letter to the Editor |
THE AUTHORS REPLY
1 Department of Genetics and Pathology, Rudbeck Laboratory, Uppsala University, SE-751 85 Uppsala, Sweden
2 Child and Adolescent Public Health Epidemiology Group, Department of Public Health Sciences, Karolinska Institute, SE-17176 Stockholm, Sweden
3 Division of Epidemiology, Stockholm Centre of Public Health, SE-17176 Stockholm, Sweden
4 Department of Social Medicine, University of Bristol, Bristol BS8 2PR, United Kingdom
(e-mail: finn.rasmussn{at}ki.se)
We thank Drs. Bernsen and Nagelkerke (1
) and Dr. Zhang (2) for their observations on our study (3).
Bernsen and Nagelkerke (1) are concerned that we did not control for smoking in our analysis. Data on smoking were not available in the linkage forming the basis of our study; this information was only available for men conscripted in 1969–1970. Less than 5 percent of our 1.3 million study members overlapped with the 49,000 included in the analysis by Hemmingsson and Kriebel (4). Smoking is associated with a low body mass index, increased levels of mental illness, and alcohol misuse (4), but the associations with markers of mental health and suicide are unlikely to be causal (5). For example, the dose-response effects of smoking, after adjustment for important confounders, have been shown to be similar for the risk of suicide and the risk of being murdered, indicating that smoking is likely to be a noncausal marker of susceptibility to the mental health states preceding suicide (5).
Zhang (2), on the basis of findings from the Third National Health and Nutrition Examination Survey, points out a potential sex difference in the association between body mass index and suicide in relation to reported episodes of nonfatal self-harm. This warrants further investigation and highlights the importance of replicating our findings in females. However, we would urge caution in generalizing associations with nonfatal self-harm to suicide. The epidemiology of self-harm and the epidemiology of suicide are quite different. In high-income countries, rates of suicide are approximately 3–4 times higher in males than in females, and the lowest rates are seen among persons aged 15–24 years (6). In contrast, the incidence of self-harm is generally higher in females, and rates peak among persons aged 15–24 years (6).
ACKNOWLEDGMENTS
Conflict of interest: none declared.
References
- Bernsen RM, Nagelkerke NJ. Re: "Association of body mass index with suicide mortality: a prospective cohort study of more than one million men." (Letter). Am J Epidemiol 2006;164:398.
[Free Full Text] - Zhang J. Re: "Association of body mass index with suicide mortality: a prospective cohort study of more than one million men." (Letter). Am J Epidemiol 2006;164:398–9.
[Free Full Text] - Magnusson PK, Rasmussen F, Lawlor DA, et al. Association of body mass index with suicide mortality: a prospective cohort study of more than one million men. Am J Epidemiol 2006;163:1–8.
[Abstract/Free Full Text] - Hemmingsson T, Kriebel D. Smoking at age 18–20 and suicide during 26 years of follow-up—how can the association be explained? Int J Epidemiol 2003;32:1000–4.
[Abstract/Free Full Text] - Davey Smith G, Phillips AN, Neaton JD. Smoking as "independent" risk factor for suicide: illustration of an artifact from observational epidemiology? Lancet 1992;340:709–12.[CrossRef][Web of Science][Medline]
- Gunnell D. The epidemiology of suicide. Int Rev Psychiatry 2000;12:21–6.
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