Despite a growing interest in understanding the cognitive deficits
associated with major depressive disorder (MDD), it is largely unknown whether
such deficits exist before disorder onset or how they might influence the
severity of subsequent illness. The purpose of the present study was to conduct
a systematic review and meta-analysis of longitudinal datasets to determine
whether cognitive function acts as a predictor of later MDD diagnosis or change
in depression symptoms. Eligible studies included longitudinal designs with
baseline measures of cognitive functioning, and later unipolar MDD diagnosis or
symptom assessment. The systematic review identified 29 publications,
representing 34 unique samples, and 121,749 participants, that met the
inclusion/exclusion criteria. Quantitative meta-analysis demonstrated that
higher cognitive function was associated with decreased levels of subsequent
depression (r=−0.088; 95% CI: −0.121, −0.054;
p<0.001). However, sensitivity analyses revealed that this association
is likely driven by concurrent depression symptoms at the time of cognitive
assessment. Our review and meta-analysis indicate that the association between
lower cognitive function and later depression is confounded by the presence of
contemporaneous depression symptoms at the time of cognitive assessment. Thus,
cognitive deficits predicting MDD likely represent deleterious effects of
subclinical depression symptoms on performance rather than premorbid risk
factors for disorder.
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