Researchers have suggested that people with diabetes may be more prone to depression because of an interaction in this group between high blood sugar levels and a neurotransmitter associated with depression. The team presented their findings at the joint meeting of the International Society of Endocrinology and the Endocrine Society: ICE/ENDO 2014 in Chicago, IL.

Previous research has suggested links between diabetes and depression, but scientists have been unsure of the mechanism driving this association.

In 2010, Medical News Today, reported on a study by researchers at Harvard School of Public Health in Boston, MA, which explored the relationship between depression and diabetes in a sample group of 65,381 women. The Harvard team found that not only were women with diabetes at increased risk of becoming depressed, but that depressed women were also at increased risk of developing diabetes.

The researchers from that study found that women with depression had a 17% higher risk of developing diabetes - and women taking antidepressants had a 25% higher risk of developing diabetes - than women without depression.

They also found that women with diabetes had a 29% higher risk of depression - and women taking insulin had a 53% higher risk of depression - compared with women without diabetes.

"Depression may result from the biochemical changes directly caused by diabetes or its treatment," the authors hypothesized, "or from the stresses and strains associated with living with diabetes and its often debilitating consequences."

This hypothesis is addressed by the researchers behind the new study - Nicolas Bolo, PhD, from Beth Israel-Deaconess Medical Center, and Dr. Donald Simonson from Brigham and Women's Hospital, both in Boston.

Biochemical mechanism may explain depression-diabetes association

"It was traditionally thought that patients with type 1 or type 2 diabetes have higher rates of depression than their nondiabetic peers because of the increased stress of managing a complex chronic disease," Bolo and Simonson write.

"Our results suggest that high blood glucose levels may predispose patients with type 1 diabetes to depression through biological mechanisms in the brain."

Bolo and Simonson studied three men and five women (average age 26) with type 1 diabetes and compared them with a control group of six men and five women (average age 29). None of the participants were depressed.

Using functional magnetic resonance imaging, the scientists measured the levels of glutamate - a neurotransmitter linked to depression at high levels - in the subjects' brains. Participants were scanned both when their blood sugar level was normal - at 90-110 mg/dL - and when it was moderately elevated, at 180-200 mg/dL.

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Raising blood glucose levels also raised the levels of glutamate - a neurotransmitter linked to depression - in the diabetic patients, but not in the control group.

The authors found that when the blood sugar level was raised, the strength of the connections between regions of the brain involved in self-perception and emotions became weaker in the diabetic patients than in the healthy control subjects.

Raising blood glucose levels also raised the levels of glutamate in the diabetic patients, but not in the control group. Elevated levels of glutamate in the diabetic patients corresponded with worse scores on a depression questionnaire.

However, the researchers note that although the diabetic group reported worse scores than the control group, the scores were still well below the range for major depression.

Dr. Bolo believes that the team's findings "may enable the development of more targeted approaches to treating depression in diabetes."

In 2013, Medical News Today reported on a study that found pain and depression in women with type 2 diabetes may be reduced by vitamin D2 supplements.