Beyond depression: mental disorders in diabetes
It has been known for several years that a strong bidirectional relationship exists between diabetes and depression. Observational studies show that depression usually predates diabetes and that the presence of depression increases the risk of future diabetes; but diabetes also increases the risk of subsequent depression. However, most studies were done in Europe and the USA, and the coexistence of other mental disorders as an explanatory factor had not been systematically investigated. A new study in Diabetologia by Peter de Jonge and his international colleagues has used the framework of the World Mental Health surveys to examine the relation between a wide range of mental health disorders and diabetes diagnosis. Their data support the focus on depression as an independent risk factor for diabetes, but also suggest that this focus should be extended to impulse control disorders.
Given the strong epidemiological relation between depression and diabetes, much attention has been given to early identification and treatment of depression as a means to reduce the burden of diabetes. However, as the authors of this study noted, depression often co-occurs with several other mental health disorders—not only with anxiety disorders but also with many of the other Diagnostic Statistical Manual, 4th edition (DSM-IV) mental disorders such as eating disorders, and alcohol abuse. Thus the authors did this new study, within the framework of the World Mental Health Surveys[a] to examine the associations between a wide range of DSM-IV mental disorders and diabetes diagnosis. This approach enabled them to investigate the association between first onset of mood, anxiety, impulse control (including eating disorders) and substance use disorders with diabetes diagnosis in a large international sample, with data coming from 19 countries: Colombia, Mexico, Peru, USA, Shenzhen (China), Japan, New Zealand, Belgium, France, Germany, Italy, the Netherlands, Romania, Spain, Portugal, Israel, Iraq, the UK (Northern Ireland) and Poland. More than 50,000 participants were included in the analysis. The authors identified 2,580 cases of adult-onset diabetes (diagnosed in those aged 21 years and over). Although all 16 DSM-IV disorders were associated with diabetes diagnosis, the same was not true after adjustment for the presence of other mental health conditions. After this adjustment, only depression (30% increased risk), intermittent explosive disorder (60% increased risk), binge eating disorder (2.6 times increased risk) and bulimia nervosa (2.1 times increased risk) independently increased the risk of diabetes diagnosis. A relation between Eating disorders and type 1 diabetes has been acknowledged before, but this study extends this relationship to type 2 diabetes. Early glucose dysregulation and obesity-associated eating disorders may mediate the future risk of diabetes but based on the fact that they also found a relation between intermittent explosive disorder and diabetes the authors hypothesize that an alternative explanation might be a dysfunction of serotonin signalling already present in early life. The sequence would then be that serotonin dysfunctioning gives rise to impulse control disorders and problematic eating behaviour, which in turn would increase the risk of obesity and diabetes, and possibly depression. While their data are only hypothesis-generating, this could prove a useful avenue of thought to find new preventive strategies. Both for the clinician working with patients with mental disorders and for the clinical diabetologist these data serve as a reminder to look beyond the horizon of the single disease to the full complexity of diabetes and mental health.
^ The World Mental Health Surveys are a series of survey studies across the world, using the same methodology, including the way the psychiatric disorders are assessed (with a standardised interview, the World Health Organization’s ‘Composite International Diagnostic Interview’ /CIDI)