Cerebrovascular disease may be causal or a vulnerability factor in late-onset depression and may explain the high rate of depression in older adults with diabetes. We explored a wide range of potential explanatory variables of depression in a longitudinal study of older diabetic subjects to investigate the vascular depression hypothesis in these patients.

Many studies indicate that diabetic subjects are at greater risk of depression than non-diabetic individuals from the general population. A meta-analysis of 42 studies concluded that the prevalence of comorbid depression in diabetic subjects was 11% when depression was assessed by diagnostic interview and 31% when assessed by self-report questionnaire.

The combination of diabetes and depression in older subjects increased several-fold the likelihood of chronic complications, disability and death. Depression in diabetes occurs most commonly in middle or younger age but there is evidence that the prevalence in older patients is higher than expected.

Potential causes of depression in chronic disease include psychosocial factors related to the burden of disease and/or pathophysiological changes in neuroendocrine or immune function. In addition, late-life cerebrovascular disease may predispose to or precipitate depression. Diabetes and hypertension, which are potent risk factors for cerebrovascular disease, may also contribute to an increased risk of depression through vascular mechanisms. This so-called vascular depression has a distinctive clinical phenotype that includes onset in later life, characteristic phenomenological features, and greater disability and more severe cognitive impairment than depression without cerebrovascular disease.

Most studies of depression in diabetes have used symptom inventories that tend to overdiagnose the condition in comparison with diagnostic interviews and none has considered specific depression syndromes in older patients. This latter observation is important because, although major depression may be most strongly associated with clinical outcomes, subsyndromal depressive disorders are common in old age and may carry an adverse prognosis.

We studied major and minor depression in a sample of older diabetic subjects from a well-categorised, longitudinal, observational study in order to determine whether cardiovascular risk factors and cerebrovascular disease were risk factors for depression and whether depression in older subjects with diabetes had the clinical features of vascular depression.

We recruited 207 subjects with diabetes selected for potential cognitive deficits from an existing observational cohort study (average age 75.7 ± 4.6 years, 52.2% men) for an assessment of depression using a standardised diagnostic instrument (Cambridge Examination for Mental Disorders of the Elderly — Revised). All subjects underwent a detailed clinical assessment at baseline and at follow-up (after 7.5 ± 1.1 years).

Major depression was present in 45 subjects (21.7%) and minor depression in ten (4.8%). A positive history of strokes and the presence of Peripheral arterial disease were significantly associated with depression at the time of diagnosis. In a subsample of 93 cases who underwent structural neuroimaging, the presence of cerebral infarcts was also significantly associated with depression. Treatment with glucose-lowering therapy, higher serum cholesterol levels and difficulties with activities of daily living at baseline were significant predictors of depression at follow-up.

Conclusions/interpretation
A history of cerebrovascular disease was strongly associated with depression and cerebrovascular risk factors were significant predictors of depression in older diabetic patients. Our findings are consistent with the hypothesis that the excess risk of depression in older diabetic patients is related to underlying cerebrovascular disease.

Keywords 
Cerebrovascular disease - Depression - Diabetic complications - Diabetes - Longitudinal study - Old age

D. G. Bruce
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D. G. Bruce Contact Information, G. Casey, W. A. Davis, S. E. Starkstein, R. C. Clarnette, J. K. Foster, F. J. Ives, O. P. Almeida and T. M. E. Davis
(1) School of Medicine and Pharmacology, University of Western Australia, Fremantle Hospital, P.O. Box 480, Fremantle, Western Australia, 6959, Australia
(2) School of Psychiatry and Neurosciences, University of Western Australia, Fremantle, Western Australia, Australia
(3) Department of Community and Geriatric Medicine, Fremantle Hospital, Fremantle, Western Australia, Australia
(4) Ageing and Alzheimer’s Unit, Edith Cowan University, Perth, Western Australia, Australia
(5) SKG Radiology, Hollywood Private Hospital, Perth, Western Australia, Australia

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