Individuals with young onset type 2 diabetes at substantially higher risk of depression

• Study of 1.4 million UK and US adults with type 2 diabetes reveals that the risk of depression at the time of diabetes diagnosis is increasing rapidly across all age groups, particularly in those under 40.
• Overall, the prevalence of comorbid depression in the UK has risen from 29% in 2006 to 43% in 2017, and in the USA from 22% to 29%.
• Authors call for regular mental health screening from the time of type 2 diabetes diagnosis, especially for those who are younger than 50 years old.

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Men and women who are diagnosed with type 2 diabetes (T2D) before the age of 40 are far more likely to experience depression than those who develop T2D later in life, regardless of whether or not they have other underlying illnesses, according to new research published in Diabetologia (the journal of the European Association for the Study of Diabetes [EASD]).

The findings also indicate that there has been a startling increase in rates of depression at the time of T2D diagnosis in the UK and USA across all age groups—rising from 29% and 22% in 2006 to 43% and 29% in 2017, respectively.

The study analysed nationally representative electronic medical records of nearly 1.4 million UK and US patients with T2D over 11 years, making it the first to examine population-level trends in the prevalence of depression at the time of T2D diagnosis.

“Our findings clearly highlight the mental health implications of developing type 2 diabetes at a young age and the importance of efforts to prevent diabetes early in life”, says lead author Professor Sanjoy Paul of the University of Melbourne, Australia. “Proactive management of coexisting depression through timely screening, early diagnosis and drug treatment may lead to improved blood sugar control in people with diabetes, delayed onset of complications, and ultimately lower healthcare costs.”

People with T2D are more likely to suffer from depression and vice versa. Experiencing depression and T2D at the same time is associated with difficulty keeping up with medications, lower quality of life, and increased risk of complications and even death, with average medical costs for US patients with diabetes and symptomatic depression more than double those with diabetes and no depression [1].

T2D is the most common form of diabetes and usually occurs in middle-aged and older people. However, onset at a younger age is becoming more common globally and is typically a more aggressive form of the condition that leads to earlier development of complications and higher rates of hospitalisations.

Nevertheless, little is known about the specific burdens of depression in young-onset T2D (diagnosis before the age of 40) and usual-onset T2D (diagnosis at age 40 or older), or the relationship between age at diagnosis, other comorbidities, and risk of depression.

To find out more, Professor Paul and colleagues from the University of Melbourne, Australia, analysed electronic medical records from 230,932 adults (57% men) at GP practices cross the UK and over 1.1 million US adults (46% male) from ambulatory and primary care practices across the USA, diagnosed with T2D between 2006 and 2017.

Of those patients, 1 in 3 in the UK (80,930) and 1 in 4 in the USA (287,942) had depression when they were diagnosed with T2D. The average age of diagnosis with T2D was 58 years in the UK and 60 years in the USA.

Individuals diagnosed with T2D before the age of 40 had, on average, a higher HbA1c (average blood sugar level) at diagnosis than those diagnosed at an older age, and were significantly more likely to be living with obesity. Levels of cardiometabolic comorbidities such as cardiovascular diseases and chronic kidney disease were highest in those aged 70-79 years in both countries (UK 70%/US 65%; tables 1 and 2).

The analyses found that rates of depression have been significantly increasing over the 11-year period in both countries across all age groups in both men and women, with women more likely to have depression than men (figure 1).

When other relevant factors including deprivation status (UK only), smoking status, ethnicity (USA only), and high blood pressure were adjusted for, men in the UK diagnosed with T2D before the age of 40 were 23-57% more likely to develop depression than males who were diagnosed at the more typical age of 50 or older, while younger women had a 20-55% greater risk of depression than those aged 50 or older.

Similarly, in the USA, men diagnosed with T2D between the ages of 18 and 39 years were 5-17% more likely to develop T2D than those who were diagnosed at the age of 60 or older, while younger women had a 8-37% greater risk.

“Despite the sociodemographic and healthcare system differences between the UK and the USA, all age groups experienced significant increases in comorbid depression” says co-author Dr William Polonsky from the University of California, USA. “It’s likely that the 3-4% average annual increase in rates of comorbid depression is due to a greater awareness about the association between diabetes and depression and increased likelihood of diagnosis in primary/ambulatory care, as well as better record-keeping following the roll out of electronic medical records.”

According to Professor Paul, “The higher risk of developing depression with young-onset diabetes may be partially explained by a higher burden of other risk factors including obesity and smoking. But what we’re seeing in these data is very troubling, and we need to dig deeper to understand the causes and effects of cardiometabolic risk factors before and after type 2 diabetes diagnosis on depression risk in different age groups, sex and ethnicities.”

The authors note that the study is observational and point to several limitations, including that under-reporting of depression and miscoding of conditions in electronic records is common. They also note they were unable to account for some potentially important confounders (such as physical activity, education and income) due to the lack of reliable recording of these social variables within electronic health records—which may have influenced the results.

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