Is There a Link Between High Blood Glucose and Depression?

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Depression and diabetes: a large population-based study of sociodemographic, lifestyle, and clinical factors associated with depression in type 1 and type 2 diabetes, by A. Engum and colleagues. Diabetes Care 28:1904–1909, 2005.

What is the problem and what is known about it so far?

Studies in the past have shown that there is a connection between depression and diabetes. Depression has been linked with high blood glucose, problems that come from having diabetes (like eye problems and gaining weight), and the physical limitations that result from diabetes, such as not being able to eat certain foods and having to take medications. However, it is unknown whether the problems that are linked with depression in type 1 and type 2 diabetes are different from those in the general population.

Why did the researchers do this particular study?

Previous research has shown that there is a strong connection between people having recurring or long-lasting illnesses and having depression. Studies have also tested the link between depression and aspects of a person's lifestyle, such as whether the person is married, is rich or poor, is obese, smokes, or has any disabilities. Researchers wanted to find out if there is a specific connection between diabetes and depresssion that is different from the connection between depression and other factors.

Who was studied?

Researchers invited the 92,100 people living in Nord-Trømdelag County, Norway, to take part in the Nord-Trømdelag Health Study. The study was conducted from 1995 to 1997 and was made up of the 65,648 members of the community between 20 and 89 years of age who responded to the invitations. Of the individuals studied, 223 had type 1 diabetes, 958 had type 2 diabetes, and 359 had other subtypes of diabetes or were unclassified.

How was the study done?

Researchers looked at health and lifestyle aspects such as education levels, marriage, smoking, and exercise among people with and without diabetes. They also looked at the connection between high blood glucose and depresssion. Patients rated their own levels of depression using a well-known depression scale.

What did the researchers find?

There were three main findings in the study. First, long-lasting physical illnesses were linked with depression in people who had type 2 diabetes but not in people who had type 1 diabetes. People with type 2 diabetes who did not have any other health problems had the same odds of being depressed as people without diabetes.

Second, high blood glucose was not connected with depression in people with any type of diabetes.

Lastly, the factors that were connected with depression in type 1 and type 2 diabetes were also connected to depression in the general population. The researchers concluded that just having diabetes does not necessarily make a person more likely to be depressed. However, people with diabetes are more likely to also have other illnesses, and the presence of several diseases can increase the likelihood of depression.

What were the limitations of the study?

There were several limitations to the study. The system used to measure depression only looked at depressive symptoms and did not confirm the presence of depression. It also relied on the people's own reports of their symptoms, which sometimes isn't very accurate.

The study only looked at current illnesses, not lifetime problems, and the study group was predominately white patients.

The diagnosis of diabetes and other diseases was self-reported, which could mean people may not have known they had a certain illness or may not have reported some things. Also, it is possible that members of the nondiabetic population could have undiagnosed diabetes.

What are the implications of the study?

Many factors, including lack of exercise, disabilities, and being in poor health, contribute to depression. There was no evidence from the study that diabetes alone is directly connected to depression. However, the physical limitations, lifestyle differences, and other illnesses that develop in people with diabetes can make diabetic patients more likely to become depressed.

For more information

History of depression increases risk of type 2 diabetes in younger adults, by L.C. Brown and colleagues. Diabetes Care 28:1063–1067, 2005.

Depression

Diabetes -- A Different Kind of Low, by S. Guzman. Diabetes Forecast, October 2004.