It is well established that depression is common in late life and associated with a range of consequences for the individual and those close to them. These consequences include higher use of health services and declines in functional ability (Luppa et al., Reference Luppa, Heinrich, Angermeyer, König and Riedel-Heller2007), not to mention negative subjective experiences, such as reduced engagement with, and enjoyment of day-to-day activities. Depression in late life is a heterogeneous condition made more complex by the links between depression, cognitive decline and dementia. The “Vascular Depression Hypothesis” suggests that a subset of late life depressive disorders are caused by cerebrovascular disease (Taylor, Reference Taylor2014), but questions about the relationships between depression and cognitive decline remain unanswered. The paper chosen as the paper of the month in this issue of International Psychogeriatrics addresses one of these questions, namely, whether we can identify clinical signs and symptoms that predict cognitive decline in individuals diagnosed with depression. This question is of great clinical relevance, as not all patients and clinicians will have access to the neuroimaging or detailed neuropsychological assessment that could cast light on risk for cognitive deterioration.

Riddle and colleagues (Reference Riddle, McQoid, Potter, Steffens and Taylor2015) therefore started from the premise that it is important to identify factors predictive of cognitive decline that could be elicited from the clinical history sought from either patients or relatives. They hypothesized that personal and social functioning are two candidates for this role. Testing this hypothesis clearly requires a longitudinal design, and this study followed 299 older adults for an average of seven years. At entry into the study, all were cognitively intact (scoring >25 on the Mini-Mental State Examination (MMSE), Folstein et al., Reference Folstein and McHugh1975) and met DSM-IV criteria for a major depressive disorder. Disability and social support were also assessed at this time. A major strength of this study is the annual evaluations of neuropsychological functioning and dementia status. Riddle and colleagues’ data showed that just under half of this cohort developed mild cognitive impairment or dementia during the course of the study, and that greater baseline deficits in independent activities of daily living, especially keeping track of money and ability to prepare meals, predicted conversion rates. In contrast, social support did not predict subsequent cognitive status.

These results are important for several reasons. Firstly, they provide clinicians with specific indicators about which enquiry can be made relatively easily. Difficulties with financial affairs and domestic routines such as cooking are probably manifestations of dependency that have their roots in declining executive functioning. Therefore, enquiring about functional ability may provide a window into underlying pathological processes. Secondly, the study helps to elucidate the relationships between depression, dementia, and disability. While these are no doubt multi-directional, the design of this study allows us to see that disability in Independent Activities of Daily Living (IADLs) precedes cognitive decline in older adults with depression. Further research is needed to explore the pathways involved in this association. Is it the case that the apathy and lack of motivation that characterize depression result in withdrawal from activities and the cognitive stimulation they provide? Or are the difficulties in IADLs subtle indicators of cognitive change that does not yet show up in standard neuropsychological testing?

The lack of a relationship between social support and cognitive decline is intriguing, given the data from some studies indicating a link between lack of social engagement and cognitive decline. It is probably important to distinguish between different types of social engagement: social support may be elicited in response to emergent need, whereas having social connections may indicate positive and active community engagement. Holwerda et al. (Reference Holwerda2014) found that feelings of loneliness, but not social isolation, were associated with an increased risk of developing dementia. Clearly, this is also an area where the relationships are complex, and would repay further investigation.

In summary, the study by Riddle and colleagues provides clinically useful insights, but also raises questions for future research. Given the high prevalence of both depression and dementia in an ageing world, these questions are timely and pressing.