Sarah Tjeerdsma is a Cognitive Neuroscience Research Master student at Radboud University, Nijmegen, the Netherlands. She is interested in neuropsychiatric disorders and wrote this blog post for a course in science communication.
You might know someone, or be someone, with type 2 diabetes. But did you know that type 2 diabetes often co-occurs with psychiatric symptoms, such as depression or ADHD? Often, however, these psychiatric complaints are attributed to diabetic symptoms, and therefore the mental health issues remain untreated. Besides the direct effects these issues might have on daily life, psychiatric issues can also lead to problems with the management of diabetes. Therefore, it’s very important to increase awareness of this co-occurrence, so that this can be recognized sooner by health care professionals, but also by people with diabetes themselves. The sooner psychiatric issues are noticed, the sooner these can be treated, and the sooner a plan towards optimal diabetes management can be designed. And besides, the better diabetes is managed, the lower the risk of developing mental health complications.
In this blog I will first explain what type 2 diabetes is, and will then zoom in onto two conditions that frequently co-occur with diabetes: depression and ADHD.
What is Type 2 Diabetes?
In type 2 diabetes the body does not respond well to the insulin inside the body anymore. This is called insulin resistance. Insulin is a hormone produced by the pancreas that keeps the blood sugar at the appropriate level. Insulin does this by taking up sugar out of the blood and storing it in muscles and fat tissue. Furthermore, insulin reduces the sugar production by the liver. When insulin cannot execute its function properly anymore, the sugar levels in your blood rise too much, which is dangerous for the body.
Nine out of ten people with diabetes have type 2 diabetes. The other 10% has type 1 diabetes, in which the body does not produce enough insulin because the body attacks its own insulin production cells. This often starts already in childhood. Type 2 diabetes is often caused by an unhealthy lifestyle – think of a diet including too much fat and not having enough physical activity – in combination with genetic risk factors. Ageing also increases the risk: the older you get, the higher the risk of developing type 2 diabetes. People with type 2 diabetes are often advised to change their lifestyle by adapting their diet and increasing physical activity. This can be combined with medication, and occasionally with insulin injections.
Type 2 diabetes can co-occur with several psychiatric symptoms associated with, for example, depression, ADHD, schizophrenia, and anxiety disorders. During diagnosis of diabetes, often no special attention is paid to psychiatric complaints. It may also be that symptoms of psychiatric conditions overlap with the symptoms of diabetes and are therefore missed by the health care professional. But why do psychiatric complaints so often co-occur with type 2 diabetes? To answer this question, I will elaborate on two of the most common co-occurring disorders in the next paragraphs: depression and ADHD.
Depression and Type 2 Diabetes
One of the most reported psychiatric disorders that co-occur with type 2 diabetes is depression, a complex condition that can disrupt all aspects of life – social, behavioural, psychological, and physical. People with diabetes are twice as likely tosuffer from depression as compared to the general population. Some symptoms of depression can also be found in diabetes; think of weight loss, lethargy (feeling tired and lacking energy and motivation), and loss of libido. Therefore, health care professionals might not immediately think of depression when these symptoms are encountered during diabetes diagnosis. But the co-occurrence of type 2 diabetes and depression often results in difficulties in self-management of diabetes. Poorer adherence to diabetes medications and dietary recommendations may be due to depressive symptoms such as lethargy, anhedonia (diminished ability to experience pleasure) and a lack of concentration. Therefore, it is very important to recognize these depressive symptoms early on, to optimize management of diabetes.
The link between these two conditions goes both ways, meaning that depression affects the risk of developing type 2 diabetes, just as well as diabetes affects the risk of developing depression. The exact mechanisms through which these two conditions affect each other are not entirely clear yet. But there are many ideas circulating in the scientific world, of which I will explain a few below.
People with depression are often less attentive to a healthy lifestyle and therefore might show poorer health behaviours, such as smoking, physical inactivity, and high caloric intake. And I explained above, an unhealthy lifestyle increases the risk of developing type 2 diabetes. Besides these behavioural factors, there are biological mechanisms underlying depression that might increase diabetes risk. Dysregulation of the stress system can lead to high cortisol levels, which in turn can lead to inflammation. This can also affect insulin sensitivity, and perhaps even lead to insulin resistance, and therefore contribute to the development of diabetes.
The other way round, type 2 diabetes can cause inflammation in different types of tissues, including the brain. This can activate neural pathways that are involved in the development of depressive symptoms. Type 2 diabetes is also associated with smaller volumes of brain areas that are also affected in depression. Besides, the diagnosis of diabetes itself can also lead to stress since this may require substantial changes in lifestyle, and might lead to uncertainty about the future and fear of potential complications. This can also be a risk factor for depressive symptoms, but is usually in itself not enough to cause a depressive disorder.
ADHD and Type 2 Diabetes
Multiple studies have shown that there is a link between ADHD and type 2 diabetes: people with ADHD are more likely to develop diabetes later in life – especially children, adolescents, and young adults. However, research investigating this association is still in very early stages. Therefore, the mechanisms underlying the relationship between ADHD and diabetes are not clear yet. But let’s look at some of the ideas that have been proposed so far.
People with ADHD often struggle with inattention, disorganization, and forgetfulness. Because of these issues it may become difficult to adhere to a healthy lifestyle, just as we saw was the case with depression. They may forget to do groceries and therefore end up ordering less healthy food, or might find it difficult to stick to an exercise plan. An additional explanation for more unhealthy eating could be the lack of dopamine in the “ADHD-brain”. Therefore, the brain craves more dopamine, which can be released as a result of the intake of simple carbohydrates and high-sugar foods (although there are also healthy alternatives, such as certain fruits and nuts). And as mentioned before, an unhealthy lifestyle is a risk factor for type 2 diabetes. These behaviours can also impair management of diabetes, once diagnosed.
Another suggestion for a biological mechanism that may explain the link between ADHD and type 2 diabetes has to do with proinflammatory cytokines. These are signalling molecules that promote inflammation. Studies have found that some types of these cytokines are present in higher amounts in people with ADHD as compared to people without ADHD. And some of these cytokines are also more present in people with diabetes. However, these are results from different studies and have not been investigated together yet. Therefore, researchers are looking into this mechanism to better understand it.
How can Type 2 Diabetes and Psychiatric Conditions Better be Managed?
There are many indications of increased prevalence of psychiatric symptoms in people with type 2 diabetes, and this relationship often seems to go both ways. Although there are some theories, we need to do more research to better understand the mechanisms of these co-occurrences, and possibly adapt the diagnosis and treatment strategies. The more we know about this, the better interventions can be designed to deal with these conditions.
If you notice that you are struggling with adhering to the medical advice you have received regarding diabetes and recognize symptoms of depression, ADHD, or have other mental health issues, discuss this with your GP or other health care professional. Undiagnosed psychiatric symptoms could explain some of the struggles you’re experiencing. Being aware of this is very important, as this could improve the mental health issues as well as diabetes management.
The EU-funded research consortium PRIME investigates the link between insulin signalling and mental health. You can find more information at www.prime-study.eu
Further Reading