Background Affective problems are common, involving one in five individuals across their lifetime. Affective problems increase the risk for subsequent dementia and cognitive impairment, but the nature of this association is not yet clearly understood. Symptom severity is known to raise the risk, but it is unclear whether this risk is cumulative. We investigated prospective associations between lifetime severe affective symptoms and subsequent mental status and cognitive decline in a population-based sample aged 69 years, still mostly free of dementia, controlling for potential confounders.
Methods Complete data from1059 study members from the Medical Research Council National Survey of Health and Development (NSHD, the 1946British birth cohort) were analysed. Prospectively-assessed affective symptoms at ages 13–15, 36, 43, 53, 60–64 and 69 were used to generate severe (case-level) binary indicators of affective symptoms at each age which were then summed to give a cumulative score and operationalised as 0 (never case-level), 1 (case-level at only one assessment), or 2 (case-level at two or more assessments). Mental status was assessed using the Addenbrooke’s Cognitive Examination (ACE-III) at age 69. Measures of short-term memory, letter search speed and accuracy were assessed at ages 60–64 and 69. Linear regression models were conducted to investigate whether case-level affective symptoms were associated with lower mental status and cognition at age 69, conditional on cognition at age 60–64, and adjusting for gender, childhood cognition, childhood and midlife social class and educational attainment.
Results Compared with those with no evidence of affective problems, those with case-level symptoms at only one assessment did not differ in any of the cognitive measures, before and after adjustments. However, those with case-level affective symptoms at two or more assessments had a lower ACE-III score (β=−0.88, 95%CI=−1.66,–0.10), and greater decline in short-term memory (β=−0.56, 95%CI=−1.21,–0.09), search speed (β=−11.11, 95%CI=−19.59,–2.64), and search accuracy (β=−0.71, 95%CI=−1.29,–0.13) between ages 60 and 69, before and after adjustments.
Conclusion Overall, our findings show that those with recurrent severe affective problems are more likely to have poorer mental status and faster cognitive decline. One limitation is that there may be additional confounding factors that we have been unable to account for, including the potential for reverse causality. However, this is still one of the largest prospective studies to show the association between lifetime severe affective symptoms and subsequent cognitive function. Further follow-up will determine what proportion with severe recurrent symptoms develop clinical dementia.
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