People who have depression or exhibit its symptoms are more likely to develop diabetes than those who do not, a new study says.

In their analysis of a national study, researchers from the Johns Hopkins University School of Medicine found that patients who had symptoms of depression at the beginning of the study were 42 per cent more likely to develop diabetes than subjects who didn't show signs of these symptoms.

They also found that the stronger the symptoms, the higher the risk of developing diabetes.

When the researchers looked at diabetes risk factors such as being overweight, a lack of exercise and smoking, the risk of diabetes was still 34 per cent higher among those who exhibited symptoms of depression.

The researchers, led by diabetes expert Dr. Sherita Hill Golden, speculated that depression may cause people to develop behaviours that can trigger diabetes or worsen its symptoms, such as overeating, not exercising or smoking.

"Having both diabetes and depression can make it difficult for patients to get the good clinical outcomes that we like to see for each of these conditions," Golden said in a statement.

While the researchers found that depression may be a trigger for diabetes, they also found that diabetes may in turn trigger depression.

The team found that diabetics who are treating their disease are 54 per cent more likely to suffer symptoms of depression than people without diabetes.

The researchers theorized that the stress of treating the illness might lead to the development of depression symptoms, or make pre-existing symptoms worse.

On the other hand, patients who have pre-diabetes symptoms or whose diabetes is going untreated were 25 per cent less likely to develop depression symptoms compared to those without diabetes.

The researchers could not account for these findings.

"It's important that doctors be attuned to look for both conditions in patients at risk for either diabetes or depression," Golden said.

"We may want to develop interventions for both treatments, instead of just one or the other."

The study is published in the June 18 edition of the Journal of the American Medical Association.

The researchers gleaned their findings from the Multi-Ethnic Study of Atherosclerosis (MESA), which investigated risk factors for atherosclerosis, which is a hardening of the arteries. The survey subjects were an ethnically diverse group of men and women between the ages of 45 and 84.

The more than 6,800 subjects were monitored for risk factors for atherosclerosis, which include type 2 diabetes and symptoms of depression.

Abstract:

Context Depressive symptoms are associated with development of type 2 diabetes, but it is unclear whether type 2 diabetes is a risk factor for elevated depressive symptoms.

Objective To examine the bidirectional association between depressive symptoms and type 2 diabetes.

Design, Setting, and Participants Multi-Ethnic Study of Atherosclerosis, a longitudinal, ethnically diverse cohort study of US men and women aged 45 to 84 years enrolled in 2000-2002 and followed up until 2004-2005.

Main Outcome Measures Elevated depressive symptoms defined by Center for Epidemiologic Studies Depression Scale (CES-D) score of 16 or higher, use of antidepressant medications, or both. The CES-D score was also modeled continuously. Participants were categorized as normal fasting glucose (<100 mg/dL), impaired fasting glucose (100-125 mg/dL), or type 2 diabetes ( 126 mg/dL or receiving treatment). Analysis 1 included 5201 participants without type 2 diabetes at baseline and estimated the relative hazard of incident type 2 diabetes over 3.2 years for those with and without depressive symptoms. Analysis 2 included 4847 participants without depressive symptoms at baseline and calculated the relative odds of developing depressive symptoms over 3.1 years for those with and without type 2 diabetes.

Results In analysis 1, the incidence rate of type 2 diabetes was 22.0 and 16.6 per 1000 person-years for those with and without elevated depressive symptoms, respectively. The risk of incident type 2 diabetes was 1.10 times higher for each 5-unit increment in CES-D score (95% confidence interval [CI], 1.02-1.19) after adjustment for demographic factors and body mass index. This association persisted following adjustment for metabolic, inflammatory, socioeconomic, or lifestyle factors, although it was no longer statistically significant following adjustment for the latter (relative hazard, 1.08; 95% CI, 0.99-1.19). In analysis 2, the incidence rates of elevated depressive symptoms per 1000-person years were 36.8 for participants with normal fasting glucose; 27.9 for impaired fasting glucose; 31.2 for untreated type 2 diabetes, and 61.9 for treated type 2 diabetes. Compared with normal fasting glucose, the demographic-adjusted odds ratios of developing elevated depressive symptoms were 0.79 (95% CI, 0.63-0.99) for impaired fasting glucose, 0.75 (95% CI, 0.44-1.27) for untreated type 2 diabetes, and 1.54 (95% CI, 1.13-2.09) for treated type 2 diabetes. None of these associations with incident depressive symptoms were materially altered with adjustment for body mass index, socioeconomic and lifestyle factors, and comorbidities. Findings in both analyses were comparable across ethnic groups.

Conclusions A modest association of baseline depressive symptoms with incident type 2 diabetes existed that was partially explained by lifestyle factors. Impaired fasting glucose and untreated type 2 diabetes were inversely associated with incident depressive symptoms, whereas treated type 2 diabetes showed a positive association with depressive symptoms. These associations were not substantively affected by adjustment for potential confounding or mediating factors.