ISTANBUL — The risk of comorbid depression is particularly strong in relatively young people with type 2 diabetes, according to a nationwide Norwegian study.
In Norwegian men with type 2 diabetes, the risk of unipolar depressive disorder peaked when they were in their 20s, with a prevalence 3.54-fold greater than in age-matched nondiabetic men, Dr. Line I. Berge reported at the annual congress of the European College of Neuropsychopharmacology.
In contrast, the prevalence of unipolar depression in Norwegian women with type 2 diabetes women peaked when they were in their 40s; the rate among similarly aged women without diabetes was 2.4-fold higher.
By the time Norwegian men with type 2 diabetes were in their 40s, their risk of depression was increased 2.35-fold, compared with age-matched controls, a considerable drop off from their peak rate when they were 2 decades younger, added Dr. Berge, a psychiatrist at the University of Bergen (Norway).
She presented an analysis of data for the year 2006 from the Norwegian Prescription Database, a comprehensive record of all physician-prescribed drugs for appropriately diagnosed outpatients in the nation of 4.8 million people.
Depression and diabetes are two of the most common diseases in the Western world.
The prevalence of unipolar depressive disorder among Norwegian adults in 2006 was 5.3%, while the prevalence of type 2 diabetes was 1.6%.
The overall risk of comorbid unipolar depression in individuals with type 2 diabetes was 2.54-fold greater than in people without diabetes.
The explanation for the age- and gender-related differences in comorbidity is unclear.
The Norwegian data were not adjusted for known risk factors for type 2 diabetes, such as obesity, smoking, and sedentary behavior, but it's unlikely that those potential confounders would explain the disparate findings with regard to gender and age, she continued.
This study has the strength of including the entire Norwegian population, providing a large enough sample size to look at age-related differences. The study's major limitation is that it is cross-sectional, making it impossible to say whether type 2 diabetes is a risk factor for depression or vice versa. But data from the U.S. longitudinal Multi-Ethnic Study of Atherosclerosis (MESA) suggest the relationship is bidirectional, Dr. Berge noted.
MESA prospectively followed more than 5,200 participants without baseline diabetes and showed that those with baseline depressive symptoms had a “modest” increase in new-onset type 2 diabetes during 3.2 years of follow-up, even after adjustment for potential confounders.
Similarly, those with baseline type 2 diabetes had an increased rate of new-onset depressive symptoms during follow-up (JAMA 2008;299:2751-9).
The observed bidirectionality is biologically plausible in that depression involves neuroendocrine activation and a chronic inflammatory state that can induce insulin resistance, while the burden of managing type 2 diabetes causes psychological stress which might increase depressive symptoms.
It is particularly interesting to note that study participants with impaired fasting glucose or untreated type 2 diabetes had a lower risk of developing depressive symptoms than did normoglycemic controls, according to the MESA investigators.
“These findings suggest that clinicians should be aware of the increased risk of depressive symptoms in individuals with treated type 2 diabetes and consider routine screening for depressive symptoms among these patients,” concluded Dr. Sherita H. Golden of Johns Hopkins University, Baltimore, and her MESA coinvestigators.