Is Stress the Link Between Diabetes and Depression?
Briana Mezuk, PhD
Professor, University of Michigan
American Diabetes Association Research Funding
Innovative Clinical or Translational Science
Study after study has shown that depression and diabetes are somehow linked. “People with a history of depression are up to 60 percent more likely to develop [type 2] diabetes when they get older,” says Briana Mezuk, PhD, a professor at the University of Michigan. And people who have type 1 or 2 diabetes are at higher risk for depression.
The reasons why are harder to fathom. In studies of identical twins, there are many cases in which one twin has depression or diabetes and the other doesn’t. That suggests that genes alone aren’t responsible for the link between the two conditions.
Instead, the causes may be environmental. “Depression is often a biological consequence of a social disruption or life event,” Mezuk says. Stress, in particular, seems to be a common thread for both depression and diabetes.
Chronic stress can lead to depression. At the same time, stress increases type 2 diabetes risk. Stressful situations release a cascade of hormones in the body that affect digestion, metabolism, and other important functions—part of the body’s attempt to mobilize resources in a “fight or flight” situation. Stress also prompts behaviors such as unhealthy eating, which can contribute to obesity and type 2 diabetes.
With the help of a grant from the American Diabetes Association, Mezuk is conducting research to gather more evidence that stress could be contributing to a higher risk of diabetes. At the heart of Mezuk’s study is a measurement of how people respond to stress. She’s using cortisol, a hormone produced during stressful situations, as a yardstick, comparing cortisol levels from saliva samples taken before and after a stressful situation.
When they first arrive at Mezuk’s lab, participants—all adults at high risk for developing type 2 diabetes—give an initial cortisol sample. Mezuk then asks them to do something that scares most people: Give a speech in front of a group of strangers. Unbeknownst to the study participants, their audience is instructed to stay stone-faced and silent. “Most people are nervous when they’re speaking in public,” Mezuk says. “It’s really nerve-wracking when nobody’s responding.” Indeed, the saliva sample taken after the speech typically shows higher levels of stress hormones such as cortisol. (Those cortisol levels come down, and participants are filled in on the audience’s instructions, once the task is complete.)
Based on a pilot study, Mezuk is predicting something that might seem counterintuitive at first: After a year, she expects the people with the smallest increase in cortisol levels during their stress test—those whose stress levels changed the least during their speeches—will be more likely to develop diabetes, as measured by higher blood glucose levels. “Our theory is that people who have a more blunted response are folks who progress to diabetes the fastest,” she says.
She reasons that study participants who are already dealing with a lot of stress in their lives—the kind you might feel if you lived in a dangerous neighborhood or were constantly struggling to pay your bills—wear out their body’s ability to respond appropriately to stressful situations, limiting the amount of extra cortisol it can produce.
If she’s correct, it could help doctors and patients better understand that managing stress is part of managing diabetes. “It may be that interventions like meditation or improving sleep are really helpful,” she says. “Right now, managing stress is disconnected from the rest of the diabetes prevention story.”
One of the study’s other goals is a better understanding of how income and race play into stress levels and diabetes risk. Mezuk hopes to recruit 200 participants over the next three years, half from low-income neighborhoods and half from higher-income neighborhoods.
The two groups are also evenly divided between whites and African Americans, which enables Mezuk to compare how stress contributes to diabetes across income and race. African Americans and Hispanics develop diabetes at an average of twice the rate of whites.
Mezuk thinks those numbers might be less about race, however, and more about exposure to daily difficulties of living in poverty or in low-income neighborhoods. One recent study, for example, showed that whites and blacks living in racially integrated low-income neighborhoods had similar health outcomes, including higher rates of type 2 diabetes. “If stress contributes to diabetes, we hypothesize that we will observe the same relationship between low-income whites as low-income blacks,” Mezuk says. “It’s about place, not race.”
Help Support Diabetes Science
If you would like to support diabetes research, such as that being done by Briana Mezuk, PhD, please go to diabetes.org/researchdonation.