The PTSD-Diabetes Relationship Is Not a One-Way Street

Individuals with posttraumatic stress disorder (PTSD) are thought to have an increased risk of developing type 2 diabetes. However, less is currently known about the effects of potential moderating factors—such as obesity—and whether they explain in part why PTSD is related to the risk of type 2 diabetes.

A new study published in JAMA Psychiatry helped clarify the role of obesity in the PTSD-diabetes connection, drawing data from Veterans Health Administration medical records of patients with and without PTSD from 2008 to 2015. Some of these patients were obese, while others were not.

The findings from the study were unexpected, said lead author Jeffrey Scherrer, PhD, director of research in the Department of Family and Community Medicine at Saint Louis University School of Medicine in Missouri.

“What we found in our study is that obesity is moderating the relationship between PTSD and type 2 diabetes,” said Dr Scherrer. “We looked at the incidence of diabetes in each group of patients and found, surprisingly, that obesity has the same effect of increasing type 2 diabetes risk in all patients, regardless of PTSD status.”

Essentially, these results indicate that PTSD does not directly cause type 2 diabetes. Rather, this association is likely explained by a combination of variables commonly seen among PTSD patients, including obesity.

“It is not a one-way street,” said Dr Scherrer. “Patients with PTSD are not preordained to have diabetes. There are a lot of other factors we need to consider.”

Background: Consulting the Literature

Although the majority of evidence available in current literature has demonstrated an association between PTSD and type 2 diabetes, the evidence of this relationship has been somewhat inconsistent, said Dr Scherrer.

“The existing literature has controlled for a host of confounding factors including obesity,” he explained. “However, in blocks of variables that control for obesity plus smoking plus hypertension and high cholesterol all in one adjustment, it does not allow us to see the independent contribution of obesity to this relationship.”

Although obesity is approximately twice as common in patients with PTSD than in those without PTSD, it is nevertheless the leading modifiable risk factor for type 2 diabetes in the general population. As many as 44% of type 2 diabetes cases in the general population are due to obesity.

With this in mind, Dr Scherrer and colleagues wondered to what extent obesity contributes to the elevated type 2 diabetes risk observed among PTSD patients. This led them to conduct their study examining whether obesity would still remain an independent risk factor for type 2 diabetes among patients with PTSD after controlling for obesity.

Dr Scherrer and Colleagues Investigate

The study included 3450 patients with PTSD (mean age: 42.8 years) and 2204 patients without PTSD (mean age: 47.7 years), all of whom were free of prevalent PTSD and type 2 diabetes for 12 months prior to the index date of the study.

Cox proportional hazard models were used to estimate whether the relationship between PTSD and incident type 2 diabetes remained independent of obesity—defined as a body mass index of 30 kg/m2 or higher. This was assessed both before and after controlling for obesity. Subsequently, the models were expanded by accounting for psychiatric disorders, psychotropic medications, physical conditions, smoking status, and demographics.

Additional Cox models were used to compare incident type 2 diabetes risk among patients with and without PTSD and with and without obesity.

Ultimately, Dr Scherrer and his team found that controlling for obesity drastically affected the magnitude of the PTSD-type 2 diabetes relationship.

Before adjusting for obesity, the hazard ratio [HR] for the age-adjusted association between PTSD and type 2 diabetes was 1.33. After adjusting for obesity, the HR dropped to 1.16.

“When we did not control for other factors, we found a 33% increased risk of type 2 diabetes among patients with PTSD,” Dr Scherrer said. “But when we accounted for the contribution of obesity to this relationship, the magnitude of the relationship decreased from 33% to 15%, and it was no longer statistically significant.”

In patients with PTSD, the age-adjusted incidence of type 2 diabetes was 21.0 per 1000 person-years in those who were obese vs 5.8 per 1000 person-years in those who were not obese. The corresponding age-adjusted incidences of type 2 diabetes for patients without PTSD were not much different: 21.2 per 1000 person-years in those with obesity vs 6.4 per 1000 person-years in those without obesity.

From these findings, Dr Scherrer and colleagues were able to conclude that patients with PTSD who were not obese likely did not have an elevated risk of type 2 diabetes. In fact, their risk of developing type 2 diabetes was not much different than that of the general population.

Contrastingly, the elevated risk for type 2 diabetes observed among obese PTSD patients was likely associated with their obesity. As a result, their diabetes risk may not be a lifetime risk and could potentially be reduced by means of lifestyle modifications.

“I did not expect the obesity effect modification to be of this magnitude,” said Dr Scherrer. “I originally anticipated that we would see some reduction in the risk of diabetes, but not to the magnitude that we observed. So, I have to admit that the strength of the role of obesity in this relationship was greater than I initially thought.”

It is important to note, however, that the degree of this obesity effect modification could have been stronger due to the average age of patients included in the sample, he added.

“The sample leaned towards patients who were relatively younger, meaning that we had fewer patients who might be at increased risk for type 2 diabetes due to age,” Dr Scherrer explained.

In addition to obesity, PTSD-diabetes relationship could have also been affected by a combination of other modifiable factors commonly seen in both PTSD and type 2 diabetes—including smoking, alcohol and drug abuse, sedentary lifestyle, and poor diet—and how these factors interact with other physiological changes in these patients, said Dr Scherrer.

Next Steps in Research

There is still work to do with respect to uncovering PTSD’s relationship with other health conditions including cardiovascular disease—a potential association that Dr Scherrer and his team have sought to explore further.

“We recently performed a similar analysis focused on various other moderators and their effects on the relationship between PTSD and cardiovascular disease,” he said. “That paper is about to undergo review.”

In addition, Dr Scherrer and colleagues will soon assess the trajectory of PTSD severity, and how changes in symptoms over time may influence health behaviors and outcomes such as obesity, diabetes, and cardiovascular disease.

“Now, we aim to determine if treating PTSD is associated with greater engagement and success in weight loss programs,” said Dr Scherrer. “If so, it raises questions about whether we should combine both of these interventions at the same time. However, the evidence for that is still pending.”

The Take-Home Message

The findings from Dr Scherrer’s study may offer some hope for PTSD patients with obesity who have an elevated risk for type 2 diabetes, as this risk is likely modifiable.

“Some people call PTSD a ‘life-sentence,’ especially because of the host of poor health outcomes that tend to follow PTSD,” said Dr Scherrer. “Many PTSD patients identify themselves with their diagnosis, so I think it is important to empower them and help them take control of their health rather than allow them to simply assume that they are predestined to have these chronic diseases.”

The number of Americans who develop type 2 diabetes in the next 30 years will likely increase significantly due to the US obesity epidemic, according Organizations like the American Diabetes Association and the American Medical Association.

Although patients with PTSD who develop obesity are likely more predisposed to this risk, they are not necessarily doomed to poor health due to their PTSD. It is important that clinicians help convey this to their patients, said Dr Scherrer.

“I think the important clinical picture is- how do we help people with mental health conditions who feel like they cannot make lifestyle changes because they have a mental health condition?” he said.

—Christina Vogt

Reference:

Scherrer JF, Salas J, Lustman PJ, et al. The role of obesity in the association between posttraumatic stress disorder and incident diabetes [Published online August 8, 2018]. JAMA Psychiatry. doi:10.1001/jamapsychiatry.2018.2028