The link between depression and diabetes risk works the other way round too; diabetes can cause depression. Put simply, diabetes can cause depression and depression can cause diabetes, researchers from the Harvard School of Public Health wrote in Archives of Internal Medicine.

Over 10% of all US adults have diabetes; for those aged at least 60 years the figure is 23%. About 14.8 million Americans are affected by a major depressive disorder annually.

The authors explained:

    “Although it has been hypothesized that the diabetes-depression relation is bidirectional, few studies have addressed this hypothesis in a prospective setting.”

An Pan, Ph.D., and team gathered data on 65,381 adult females aged 50 to 75 to see what the relationship between diabetes and depression might be. The women had to fill in an initial questionnaire with details about health practices and their medical history. Follow-up questionnaires were completed every two years for ten years until the end of 2006.

The investigators classified participants with depression as those diagnosed with the disease by a doctor, and/or taking antidepressants. Those who said they had depression were given another questionnaire to fill in with questions about their depression, including symptoms, treatments and diagnostic tests.

During the whole study period 2,844 females developed type 2 diabetes and 7,415 were identified with depression.

Those with depression had a 17% higher risk of developing diabetes – even after the researchers ruled out certain risk factors, such as BMI (body mass index) and physical activity.

The women on antidepressant medications had a 25% higher risk of developing diabetes compared to those without depression.

The investigators also found that those with diabetes had a 29% higher risk of developing depression compared to women without diabetes. This figure prevailed even after taking into account certain risk factors.

Those taking insulin for their condition had a 53% higher risk compared to the non-diabetic women.

The authors wrote:

    “The findings from this well-characterized cohort of more than 55,000 U.S. women with 10 years’ follow-up add to the growing evidence that depression and diabetes are closely related to each other, and this reciprocal association also depends on the severity or treatment of each condition. All the associations were independent of sociodemographic, diet and lifestyle factors.”

The researchers say their findings indicate that depression has an impact on diabetes risk beyond inactivity and body weight.

They also believe that their study showed a relationship between stress and diabetes.

The authors noted:

    “A diagnosis of diabetes may lead to the symptoms of depression for the following reasons: depression may result from the biochemical changes directly caused by diabetes or its treatment, or from the stresses and strains associated with living with diabetes and its often debilitating consequences.”

They concluded:

    “Future studies are needed to confirm our findings in different populations and to investigate the potential mechanisms underlying this association. Furthermore, depression and diabetes are highly prevalent in the middle-aged and elderly population, particularly in women. Thus, proper lifestyle interventions including adequate weight management and regular physical activity are recommended to lower the risk of both conditions.”

“Bidirectional Association Between Depression and Type 2 Diabetes Mellitus in Women”
An Pan, PhD; Michel Lucas, PhD; Qi Sun, ScD; Rob M. van Dam, PhD; Oscar H. Franco, MD, DSc, PhD; JoAnn E. Manson, MD, DrPH; Walter C. Willett, MD, DrPH; Alberto Ascherio, MD, DrPH; Frank B. Hu, MD, PhD
Arch Intern Med. 2010;170(21):1884-1891. doi:10.1001/archinternmed.2010.356

Written by Christian Nordqvist