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BACKGROUND: The cross-sectional association between impaired glucose/diabetes and depression is inconsistent. We examined the longitudinal associations between diabetes, indicators of glucose metabolism and depressive symptoms over 2 years of follow-up.

METHOD: Participants were 4338 men and women from the English Longitudinal Study of Ageing, a prospective study of community-dwelling older adults [aged 62.9 (S.D.=9.0) years, 45.2% men]. Depressive symptoms were assessed at baseline and after 2 years of follow-up using the eight-item Centre of Epidemiological Studies - Depression (CES-D) scale. Glycated haemoglobin (HbA1c) levels, fasting glucose and other biological and

behavioural risk factors were also assessed at baseline.

RESULTS: Approximately 11.5% of the sample were categorized with elevated depressive symptoms at follow-up (a score ≥4 on the CES-D). There was an association between HbA1c and depressive symptoms at follow-up [per unit increase, odds ratio (OR) 1.17, 95% confidence interval (CI) 1.03-1.33] after adjustment for age and baseline CES-D. Cross-sectionally, the probability of depressive symptoms increased with increasing HbA1c levels until the value of 8.0% after which there was a plateau [p(curve)=0.03]. Compared with those with normal fasting glucose, participants with diabetes (confirmed through self-report or elevated fasting blood glucose) at baseline had an elevated risk of depressive symptoms at follow-up (OR 1.52, 95% CI 1.01-2.30) after adjusting for depressive symptoms at baseline, behavioural and sociodemographic variables, adiposity and inflammation.

CONCLUSIONS: These data suggest that poor glucose metabolism and diabetes are risk factors for future depression in older adults. There was no evidence of a U-shaped association