Most people with type 2 diabetes (T2DM) are overweight or obese  and, compared to people without diabetes, have double the risk for depression . Aside from experiencing poor health, people with T2DM have higher incidence of functional limitations, particularly if they have poor glycaemic control .
The relationship between diabetes and depression is bidirectional [4, 5]. Up to a point, the severity of either condition seems to be associated with the chronicity of the other. For example, in community-dwelling older adults, depressive symptoms and HbA1c levels rise in tandem until HbA1c levels reach about 8%, beyond which the severity of both conditions plateau . Although behavioural (e.g. diet, exercise), neurological (activation of the hypothalamic-pituitary-adrenal and sympathoadrenal systems), and pharmacological factors have been suggested to contribute to the incidence of T2DM among people with depression, evidence suggests that the relationship between T2DM and depression is maintained when these factors are taken into account . Similarly, other factors that have been hypothesised to increase the incidence of depressive symptoms among people with T2DM (e.g. presence of comorbidies and diabetic complications) have been shown not to substantially influence the relationship between T2DM and depression [4, 7, 8]. Further exploration of biological factors may be warranted.
Associations between diabetes and physical function have been established using objective measures (e.g. activities of daily living, ADL) . Being able to maintain an active lifestyle is important for preserving or improving clinical status [10, 11] and health related quality of life (HRQL)  for people with diabetes. As people with diabetes age, maintenance of ADLs takes on greater significance, because deterioration of ADLs is associated with loss of independence and increased risks of morbidity and mortality . The relationship between physical function and HbA1c levels in people with T2DM is unclear [3, 13, 14]. Some studies suggest that higher HbA1c levels are associated with impaired physical function [3, 13], whilst other research found no evidence of this .
Compared to people without T2DM, people with T2DM have lower aerobic capacity [15, 16] as well as longer time to recover from exercise  and lower muscular strength [18, 19]. Maintaining muscular strength is important for reducing the likelihood of functional limitations . Being overweight or obese, as well as having T2DM, may make exercise more challenging, which may contribute further to loss of muscular strength and functional decline, and the cycle repeats itself.
Depression is associated with lower levels of physical  and social functioning  in people with chronic disease. In people with T2DM, the presence of complications (i.e. diabetic retinopathy, diabetic angiopathy and diabetic neuropathy) has been associated with higher prevalence and severity of both depression and functional disability (indicating lower levels of physical function) . Further, people with poor self-perceived weight control had more depressive symptoms and lower physical functioning, and that self-perceived weight control was linearly related to BMI .
People with diabetes and co-morbid depression experience diminished HRQL [24, 25]. Although relationships are thought to exist between depression and mental health components of HRQL in people with diabetes, the relationship between depression and physical functioning is not clear .
Evidence suggests that men and women may experience different levels of depression associated with T2DM . In this study, we focused on the experiences of middle-aged men to exclude the potential effects of menopause (metabolism and psychological). The aims of the current study were (a) to determine whether there were differences in depressed mood between overweight/obese men with and without T2DM and (b) to examine the associations between depressed mood, functional measures and glycaemic control in men with and without T2DM. We hypothesized that patients with T2DM have higher depressed mood and that depressed mood would be correlated with impairment of physical function and poorer glycaemic control.