Can depression cause type 2 diabetes?

According to new research funded by Diabetes UK, depression may play a direct role in the development of type 2 diabetes.

We know from previous observational studies that people with type 2 diabetes are around twice as likely to experience depression as those without diabetes. We also know that people with depression have a higher risk of type 2 diabetes compared to people without depression.

But these previous studies didn't show any conclusive cause-and-effect relationships between diabetes and depression. This is partly because people with diabetes or depression are more likely to smoke, eat unhealthy food and live a sedentary lifestyle. These risk factors are common to both conditions, making it difficult to understand which came first.

This study used a statistical method called Mendelian randomisation, which is different to a purely observational approach. Mendelian randomisation is a way of using the natural genetic variation which exists in a population to test whether there is a causal relationship between two factors (i.e. does a change in one lead to a change in the other). It also helps to separate out the effects of other factors that could influence any link between the two (called 'confounding factors').

The researchers analysed health and genetic data from hundreds of thousands of volunteers in the UK and Finland to see whether there was a cause-and-effect relationship between depression and diabetes. This included 19,000 people with type 2 diabetes, 5,000 people with clinically diagnosed major depression and 153,000 people with self-reported symptoms of depression.

The study authors found, for the first time, that depression may directly increase the risk of developing type 2 diabetes. The researchers think that being overweight may partly, but not completely, explain the causal relationship between depression and diabetes.

They also identified seven genetic variants linked to both conditions. For example, they found variants near genes involved in insulin production and inflammation levels in the brain, pancreas and fat tissues. These biological processes could explain how depression increases the risk of type 2 diabetes.

What do the researchers say?

The researchers suggested that people with a history of depression should be assessed for their type 2 diabetes risk so they can take steps to prevent it.

Lead researcher Professor Inga Prokopenko, of the University of Surrey, said: “Our discovery illuminates depression as a contributing cause of type 2 diabetes and could help to improve prevention efforts.

"The findings are important for both individuals living with the conditions and healthcare providers, who should consider implementing additional examinations to help prevent type 2 diabetes onset in people suffering from depression."

In the study, the authors also note other potential implications. For example, they suggest that when antidepressants are offered to people with depression who are at risk of type 2 diabetes, first-choice drugs should be those that don’t affect blood sugar levels too much, such as selective serotonin reuptake inhibitors (SSRIs).

Additionally, they suggested that people with depression should be encouraged to engage in positive lifestyle habits, such as physical activity, adequate sleep, and a heathy diet.

• Find out more about the risk factors for type 2 diabetes
• Learn about whether antidepressants are safe for people with a heart condition

The BHF verdict

We know from past studies that physical and mental health are often connected. This new research is a promising step towards helping us understand the nature of that link when it comes to depression and type 2 diabetes.

Reach out to your healthcare team if you feel concerned about your risk of diabetes

If you currently experience depression, or have experienced it in the past, reach out to your healthcare team if you feel concerned about your risk of diabetes. They will be able to offer guidance and reassurance on the many positive steps you can take to prevent diabetes. This includes regular exercise, maintaining a balanced diet and managing your weight.

How good was the research?

This study has some strong points. To date, it is the largest study of its kind to examine the link between depression and diabetes. Meanwhile, Mendelian randomisation, the method used in this study, can help separate out the effects of ‘confounding factors’ (such as any differences in risk factors between groups) that could influence the results of traditional observational studies.

But the study also had limitations. Mendelian randomisation does include many assumptions, and any results should be considered in the context of other evidence. In fact, the authors note that more studies are needed to confirm the findings.

How good was the media coverage?

This research was covered in various outlets, including The Guardian, The Daily Mail and The Independent. For the most part, all three papers gave a balanced account of the research and its main findings.

The Guardian article accurately summarised the results in their headline: “Depression can play direct role in developing type 2 diabetes, says study”.

Meanwhile, The Daily Mail and The Independent both used the following headline: “Depression is a direct cause of type 2 diabetes, research suggests.” Out of context, this could sound as though people who experience depression will always develop type 2 diabetes, which isn’t the case. It may also wrongly imply that if you don’t have depression, you won’t get diabetes.

When reading these kinds of headlines, bear in mind that no study can predict your future health. Type 2 diabetes is often preventable, and this research only underscores the importance of living a healthy lifestyle to protect your physical and mental wellbeing.

What to read next...