The relationship between diabetes and depression appears to be a bit like a two-way highway, according to researchers at Johns Hopkins University School of Medicine in Baltimore. More exactly, not only can diabetes lead to depression, but depression can also lead to diabetes.

Diabetes is the fifth leading cause of death in the United States. There are some 1 million Americans living with this disease, with 6.2 million not even knowing that they have it. To make things even worse, an additional 54 million Americans have pre-diabetes, placing them at high risk for developing type 2 diabetes.

The American Diabetes Association estimates there will be nearly 50.2 million people with diabetes by 2025, especially that obesity epidemic continues to spread. Diabetes is a disease in which the body does not produce or properly use insulin. Insulin is a hormone that is needed to change sugar, starches, and other food into energy needed for daily life.

Diabetes risk factors include being overweight, sedentary, persons with a family history of diabetes and women who have babies with a birth weight of greater than nine pounds.

Type 2 diabetes can further lead to serious complications such as heart attack, kidney failure, blindness, or nerve damage that can lead to amputations. Now, according to the new study, diabetes appears to also lead to depression but the relationship goes both ways.

For the study, Dr. Sherita Hill Golden of Johns Hopkins University School of Medicine and colleagues performed two analyses, both using information from participants in the Multi-Ethnic Study of Atherosclerosis trial.

The first analysis, involving 5,201 people without type 2 diabetes at the start of the trial, found that treated type 2 diabetes was associated with a 54 percent increased risk of developing depressive symptoms over 3.2 years. On the other hand, persons with untreated diabetes were not at risk of depression.

The study surprisingly found that people with pre-diabetes or untreated diabetes were 25 percent less likely to experience depressive symptoms compared to people with normal fasting blood sugar levels.

The second analysis, involving 4,847 participants, looked at how big was the risk of developing diabetes in depressive people. The researchers found that elevated depressive symptoms were associated with a 42 percent greater likelihood of developing diabetes during the follow-up period. The stronger the depressive symptoms, the higher the chance of developing diabetes was. The risk decreased to 34 percent after adjusting factors like being overweight, not exercising, and smoking in patients with depression.

The researchers explained the link between depression and diabetes by the fact that people experiencing depression are more likely to consume more calories, be less physically active and more likely to smoke. Therefore, they are more predisposed to diseases such as diabetes.

The new findings add to the growing body of evidence showing that either depression leads to diabetes or diabetes leads to depression. However, this is the first study to look at both directions.

Dr. Golden hopes the findings will lead to increased understanding among both doctors and patients that the two conditions are so closely intertwined. She further urged doctors that treat diabetes to look for signs of depression in their patients. Previous studies linked depression with other serious conditions such as heart disease, stroke, osteoporosis and perhaps dementia.

The findings were published in the June 18 issue of the journal of the American Medical Association.