Ever since its outbreak in China, the newly identified disease termed COVID-19 (Corona Virus Disease-19) has spread rapidly through the whole world. The spread of the underlying novel virus SARS-CoV-2 (severe acute respiratory syndrome coronavirus type 2) was officially declared as a global pandemic on March 11th 2020  and has impacted every nation with a few exceptions . Over 131 million infections have been confirmed worldwide, entailing severe disease and almost 2.9 million deaths (until May 2021 ).
To reduce the transmission of this now infamous strain of corona virus, many countries announced several restrictions, as vaccinations and medications were still lacking in the beginning. These restrictions included, among others, the shutdown of public facilities, a partial prohibition of social gatherings, the restriction of entry and intensification of border controls, as well as the promotion of safety behaviour. The restrictions, while abrupt and unprecedented, were considered inevitable in order to prevent capacity overload in hospitals and to protect risk groups .
These changes in everyday-life, alarming mortality levels in some countries and related media coverage had a large impact, not only on public life and the economic development, but also on people's mental health [5, 6]. Recently published international literature investigating the mental health of different populations in the context of the pandemic, showed elevated prevalence in depression, anxiety and stress symptoms [7–12]. These findings are in line with recent research from Germany, which points toward increased prevalence of generalized anxiety symptoms, depression symptoms, distress and COVID-19 related fear in the German population during the first lock-down . Furthermore, depression, anxiety and distress symptoms in individuals with pre-existing mental illnesses appeared to have worsened considerably . Thus, pre-existing mental illness appears to be a risk factor for psychological burden, as well as being female, at younger age, a student or unemployed [15, 16].
Other risk factors for psychological burden in the context of COVID-19 include pre-existing somatic diseases like diabetes, arterial hypertension, cardiovascular or respiratory disorders [17, 18]. The pre-existing medical conditions of several somatic diseases can lead to a more severe course of COVID-19  and thus they were defined as high-risk morbidities for COVID-19 [20, 21]. Diabetes is a definite risk factor for a severe course of COVID-19 . This chronic metabolic disease is characterized by increased levels of blood glucose, affects about 422 million people worldwide and is directly attributed to 1.6 million deaths each year . Several studies reported diabetes patients to be two to three times more likely to need intensive care, when infected with COVID-19, compared to patients with less severe disease, as well as a higher mortality in diabetes patients with COVID-19 [24, 25]. In recent literature a two-way interaction between COVID-19 and diabetes is stated, in which COVID-19 leads to worsening of dysglycemia and diabetes increased severity in COVID-19 courses . Hence, patients appear to carry a double burden and need to be very careful to follow safety behaviour such as hand-washing or physical distancing  in order to minimize the possibility of infection and a severe course of COVID-19. A recent study showed that patients with diabetes reported higher COVID-19-related fear and more safety behaviour than matched controls . Moreover, Joenson et al.  found that diabetes patients worried about not being able to manage their illness and treatment if infected with COVID-19.
Consequently, this increased risk for developing a severe course of COVID-19 because of a chronic somatic disease aggravates psychological burden due to COVID-19 [11, 30]. In addition to this pandemic stress, individuals with chronic diseases such as diabetes already have an increased psychological burden due to their medical condition . The everyday-life of diabetes patients is characterized by challenges and complications resulting in considerable emotional distress , which can lead to a higher risk of mental disorders: Several studies showed higher prevalence of mental health issues in individuals with diabetes compared to individuals without diabetes , including depression and anxiety disorders [34–36]. Importantly, depression and anxiety symptoms may be associated with lower treatment adherence, which can lead to worse glycemic control and, ultimately, adverse diabetes outcomes . As pre-existing mental health illness appears to be a risk factor for psychological burden , it can be assumed that patients with diabetes suffer from various stress factors during the COVID-19 pandemic.
Thus, the COVID-19 pandemic poses a particular challenge to patients with diabetes by adding uncertainty and distress to an already stressful pre-existing condition. In order to provide adequate support for patients with diabetes it is important to understand how the COVID-19 outbreak affects them and if there are risk and protective factors. In recent investigations COVID-19-related fear, pre-existing mental illness, trust in governmental actions and the subjective level of information appeared to predict mental health impairment [13, 38]. Due to the sudden emergence of the pandemic, mental health and health status can only be measured through patients‘ retrospective assessments. As patients with diabetes suffer from various stress factors, such as an objectively increased risk of a severe course of COVID-19 and pre-existing psychological burden, their mental health and health status might be impaired since the outbreak of COVID-19. We expect the aforementioned factors to negatively impact mental health and health status of patients with diabetes.
The increasing relevance of this issue is mirrored by the rising number of publications on the subject of mental health changes due to the COVID-19 pandemic. Rather than focusing on the general health effects of COVID-19 on a population, since several representative studies have already been conducted, the aim of this study was to examine depression symptoms, generalized anxiety symptoms, distress and health status after and, retrospectively, before the outbreak of COVID-19 in individuals with diabetes. Furthermore, we aim to investigate predictors of health changes in patients with diabetes during the pandemic, in order to provide relevant insight to preventative and acute mental health services for vulnerable groups.