The Link Between Type 2 Diabetes and Psychiatric Disorders

It is difficult enough to live with mental-health conditions without having to deal with physical illnesses. Research has revealed that Type 2 Diabetes is more common in those with mental-health disorders than it is for the general population. The combination could prove to be fatal.

“When people who have pre-existing mental illnesses develop diabetes, their outcomes are much worse,” says Anne Doherty, an associate professor of psychiatry at University College Dublin. Compared to people with Type 2 diabetes who don’t have mental illnesses, “they are more likely to develop complications, and they’re significantly more likely to die younger.” The relationship goes both ways; people with diabetes also tend to have higher rates of psychiatric disorders and face worse outcomes than people without diabetes.
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As doctors and researchers strive to untangle the mechanisms underlying these links, they’re starting to integrate the treatment of these disparate diseases. “There are some studies that show that by treating depression aggressively and assertively, you can actually improve people’s diabetes control—and, overall, their lives—so it’s really quite exciting,” Doherty says.

There is a strong connection between diabetes and psychosis. A better understanding of these connections may help us to prevent or treat such disorders.

For a long time researchers knew about the association between some severe mental disorders, like depression, schizophrenia and higher incidences of Type 2 diabetes. It was not clear until recently if this link extended to other mental disorders.

Nanna Lindekilde (a University of Southern Denmark student) recently studied the relationship between Type II diabetes and several psychiatric conditions. She and her colleagues analyzed 32 systematic reviews of the topic—which were based on 245 different primary studies conducted between 1980 and 2020.

“There, in general, is an increased risk of Type 2 diabetes in people with a psychiatric disorder,” Lindekilde says. “Most research has previously focused on people with depression or schizophrenia, but we have shown an increased risk across a broad range of psychiatric disorders.”

Type 2 diabetes is thought to affect 6% to 9% of the world’s population and 10.5% of the U.S. population. Lindekilde discovered that Type 2 Diabetes rates were much higher in those suffering from psychiatric conditions. This included a 39.7% Type 2 rate for people who have a sleep disorder, and a 20.7% rate for people who suffer from a binge eating disorder. Type 2 diabetics were also found in substance abuse disorder (15%) and anxiety disorder (13%), bipolar disorder (11%), as well as psychosis (11%).

What’s more, the association between Type 2 diabetes and many psychiatric disorders goes both ways. Study after study has shown that diabetes is more common in people who are depressed than those who are diabetic.

Researchers are still trying to unravel the mystery of this relationship, although they have some intriguing hypotheses.

Complex underlying mechanisms to be deciphered

Patients with chronic diseases like diabetes and psychiatric disorders are both known to have a negative impact on their psychological health. This can increase the likelihood of developing each.

“People with psychiatric illnesses often smoke more, they may have poor nutrition, lower physical activities, so you get these knock-on effects on your physical health,” says Seena Fazel, a professor of forensic psychiatry at the University of Oxford. Depression can lead to depression making it more difficult to exercise or eat well, as well as to not follow a prescribed medication. This can all increase your risk of developing diabetes.

Proper metabolic function is dependent on sleep. Psychiatric disorders can disrupt sleep and impair a person’s metabolism, leading to an increased risk of diabetes. Certain psychiatric medication can lead to weight gain, difficulty controlling blood sugar and a greater risk for Type 2 diabetes. “In some cases, the treatment for a mental illness can actually exacerbate underlying metabolic problems,” Fazel says.

However, diabetes and other chronic diseases can cause mental problems. “Living with a chronic condition can lower your mood and also sometimes lead people to self-medicate with alcohol and drugs,” Fazel says. “People with diabetes may be more likely to get depression because of the psychological effects of the illness, such as the restriction on certain things you can do and the sort of prognosis that you think may be hopeless.”

Research has recently revealed some intriguing insights about biological pathways that could be the root cause of both diabetes as well as psychiatric disorders.

Although shared genetic paths could potentially be the culprit, there are not enough studies to draw any conclusive conclusions. As a means to explain the higher diabetes rates in schizophrenia patients, researchers have focused their attention on possible genetic overlaps between Type 2 and schizophrenia. “While it is highly likely that there are overlapping genetic mechanisms, our understanding of this architecture remains limited,” says Amir Sariaslan, a senior research fellow in psychiatric epidemiology at the University of Oxford. Both diabetes and psychiatric diseases could be attributed to inflammation. Type 2 Diabetes is more common in those who have chronic inflammation responses. People suffering from mental disorders like depression may also be at increased risk. To determine whether inflammatory pathways or molecules may be involved in both type 2 and psychiatric diseases, scientists are currently investigating them. “It’s definitely attracting a lot of research interest,” Fazel says.

Scientists also focus on the roles of some 100 trillion microbes found in the human gut. These microbes and the associated genomes make up the gut microbiome. It is possible that changes in the gut microbiome could affect brain function and metabolism. This may theoretically influence diabetes and other psychiatric conditions.

However, what little we do know is only preliminary information. “A lot of the research is happening at a lab level, and there’s probably a ways to go before it’s fully applied to human populations,” Doherty says. “I think we’re going to know an awful lot more about this area in five years’ time.”

It’s challenging to run large trials of people with psychiatric illnesses, let alone when these patients also have diabetes, but large population studies could provide hints about some of the mechanisms underlying both disorders. Lindekilde has begun a 250,000-person study to examine possible mechanisms linking a variety of psychiatric conditions and type 2 diabetes.

She says it is crucial to understand the role of the mediating mechanisms and how they differ between psychiatric disorders. This could aid in future efforts to manage or prevent these disorders.

Even worse is when they’re together

Independently, diabetes and psychiatric disorders are associated with a lower risk of dying. “On average, people with severe mental illness die 17 years younger than everybody else, which is a massive mortality gap,” Doherty says. Diabetes patients live on average 7.5 years shorter than the general population. The effects of diabetes are more severe in those born younger. Both can prove to be extremely harmful.

“When people who have pre-existing mental illnesses develop diabetes, their outcomes are much worse,” Doherty says. Doherty cites a London clinic treating diabetes complications that conducted a study on patients. Researchers found that people with major depression are three times more likely to die in 18 months after examining all patients at the clinic.

Fazel observed a similar increase of mortality in patients suffering from psychiatric conditions who also suffered from chronic conditions, such as diabetes and heart disease. People with diabetes were at greater risk of death if they had also suffered from a psychiatric disorder like depression.

Fazel calculated the mortality rates of siblings who had diabetes and those without a psychiatric disorder to account for socioeconomic and ethnic factors. “The interesting thing is elevated mortality risk still exists even if you account for these sibling models,” Fazel says.

Fazel and other researchers are continuing to investigate why a combination of diabetes, psychiatric and mental disorders can lead to higher mortality. There are some hypotheses that the combination of diabetes and psychiatric disorder could lead to delayed treatment, or even difficulty with diabetes management.

“I think these mechanisms are really very important because that’s where you can actually start to address and prevent the increased mortality,” Fazel says. “The mortality risks are very high, and that’s really a signal that this is an important challenge for health care systems to address.”

Integrative treatment

Researchers are looking at integrated treatment options for treating both diabetes and mental disorders. “Both conditions have to be managed together if possible,” Doherty says.

This begins with diagnosing the conditions that are most likely to occur in combination. Patients who have diabetes can be screened for mental disorders and vice versa. Some countries, such as the U.K., have started to include mental-health screening in diabetes care, but it’s still far from common.

General practitioners and primary care physicians can both play a vital role in early detection. Fazel says, “If family physicians identify and treat these psychiatric comorbidities early on, we know that that can improve the outcomes.”

The integration of mental and physical treatment may help to reduce mortality. “A big part of diabetes care should be mental-health care,” Doherty says. “Another thing is to embed good physical monitoring into mental-health clinics.”

In the U.S., such integrated strategies have had some success. Doherty was part of a U.K. program, Three Dimensions for Diabetes, that combined social care and mental health and provided care for diabetic patients. “It was actually extraordinary, the proportion of people that we found to have significant mental-health problems that hadn’t previously been diagnosed, and the one marker was the fact that they just weren’t able to manage their diabetes,” says Doherty.

This integrated approach proved to be extremely effective. “We found a significant improvement in diabetes control,” she says.

Future studies will explore the connection between Type 2 diabetes, a variety of mental conditions and other health issues. The goal is to find common strategies for managing both. These seemingly separate disorders are a reminder of how mental and physical health is inextricably linked. “It argues against this division that you’ve either got mental or physical health problems, because actually they do overlap,” Fazel says.


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