Does Impaired Cognition Precede Depression?

Cognitive impairment does not predict subsequent depression, even after accounting for baseline depressive symptoms and variability in cognitive function, according to a team of researchers affiliated with Duke University in Durham, NC.

Scult and colleagues conducted a systematic review and meta-analysis of 29 longitudinal studies, including a total of 121 749 participants, to determine whether cognitive function acts as a predictor of a later diagnosis of major depressive disorder (MDD) or change in depressive symptoms. Sample sizes in the included studies ranged from 43 to 50 053, with school and community samples and birth cohorts as the most common sample types. The study was conducted to investigate the “growing literature” demonstrating that depression is associated with impaired cognitive function, and that these deficits correlate with symptom severity.

Quantitative meta-analysis found that higher cognitive function was associated with decreased levels of subsequent depression (r=-0.088, 95% CI, -0.121 – 0.054, P<0.001). Consistent with previous studies, “there was a significant contemporaneous association between higher depression symptoms and lower cognitive function,” the researchers reported. However, further sensitivity analysis found that this association was “likely driven by concurrent depression symptoms at the time of cognitive assessment.”

The study has important clinical implications, according to the researchers. “Cognitive deficits predicting MDD likely represent deleterious effects of subclinical depression symptoms on performance rather than premorbid risk factors for the disorder,” they stated.

They noted that an “open question that remains for further research” concerns “whether deficits in cognitive function are likely to predict the development of more severe or recurrent depression later in life.” Moreover, the review “focused only on general cognitive function as assessed by IQ, rather than specific subtypes of cognitive function that may be more predictive of later depression.”

Despite these limitations, the researchers concluded that their review “found that, while an association is evidence between cognitive function and later depression, general cognitive function does not appear to be a risk factor for depression.” Instead, it is “more likely related to performance decrements associated with concurrent depressive symptoms.”  The clinical implications are that low cognitive function is “likely not a causal factor of depression” and that clinicians should focus on “how decreased cognitive function in the depressed state is likely to influence treatment outcomes.”

Reference

Scult MA, Paulli AR, Mazure ES, et al. The association between cognitive function and subsequent depression: a systematic review and meta-analysis. Psychol Med. 2016;14:1-17.