In this prospective cohort study of male civil servants, obesity and unexplained weight loss were both independently associated with an increased risk of suicide mortality. The association between obesity and suicide slightly strengthened when adjusted for unexplained weight loss. Our results should be considered as preliminary due to small number of suicides. However, they provide support for the possibility that weight change, and particularly unexplained weight loss, may suppress any associations between obesity and suicide (Mukamal et al., 2007
While intentional weight loss has been shown to be associated with reduced depressive symptoms (Mamplekou et al., 2005
) and other health problems, unexplained weight loss has consistently been shown to be associated with increased mortality (Wannamethee et al., 2005
). In addition, the American Psychiatric Association’s Diagnostic and Statistical Manual includes opposite pairs, such as weight gain/weight loss and hyperphagia/hypophagia, among criteria for a diagnosis of depression and weight loss has also suggested to be related to antidepressant use (Zimmermann et al., 2003
). Furthermore, there are some diseases affecting one’s weight that may also affect ones mood and lead to depression. Thus, unexplained weight loss may be a marker of depression associated with other diseases and suicide.
It has been hypothesised that depression may mediate the associations between BMI or weight loss and suicide. Unfortunately information on depression was not available in this study. However, we had data on the history of hospital admission due psychiatric illness and used this information as a proxy measure of serious psychiatric problems including depression. Only a modest part of the association between weight loss and suicide was explained by serious psychiatric problems. This does not necessarily refute the depression hypothesis as depression is only one of the causes for hospitalization due psychiatric illness. Further research is needed to determine the causal pathways and mechanisms linking adiposity, physical and psychiatric conditions, and suicide.
We found a weak inverse correlation between BMI and unexplained weight loss in agreement with previous studies (Locher et al., 2007
). However, with cross-sectional assessment it remains unclear whether people who experienced weight loss were leaner than others already before the weight change. Finally, as many other studies in the field (Mangnusson et al., 2006
; Mukamal et al., 2007
), our study sample included only men. This potentially limits the generalisability of our findings.
If replicated, our findings suggest that future studies on obesity and suicide should take into account the confounding effect of unexplained weight loss in the analysis of obesity and suicide. Unexplained weight loss may be due physical illness or a change in eating habits or both. It has been suggested that changing eating habits is a possible warning sign for suicide and might be used to spot suicide risk.