Increase in Number of Depression Symptoms Over Time is Related to Worse Cognitive Outcomes in Older Adults With Type 2 Diabetes

Abstract

Objective: Older adults with type 2 diabetes (T2D) are at increased risk for depression, cognitive decline, and dementia compared to those without T2D. Little is known about the association of simultaneous changes in depression symptoms and cognitive decline over time.

Methods: Subjects (n=1021; mean age 71.6 [SD=4.6]; 41.2% female) were initially cognitively normal participants of the Israel Diabetes and Cognitive Decline study who underwent evaluations of depression and cognition approximately every 18 months. Cognitive tests were summarized into four cognitive domains: episodic memory, attention/working memory, executive functions, and semantic categorization. The average of the z-scores of the four domains defined global cognition. Depression symptoms were assessed using the Geriatric Depression Scale, 15-item version. We fit a random coefficients model of changes in depression and in cognitive functions, adjusting for baseline sociodemographic and cardiovascular variables.

Results: Higher number of depression symptoms at baseline was significantly associated with lower baseline cognitive scores in global cognition (estimate = -0.1175, SE = 0.021, DF = 1,014, t = -5.59; p < 0.001), executive functions (estimate = -0.186, SE = 0.036, DF = 1,013, t = -5.15; p = <0.001), semantic categorization (estimate = -0.155, SE = 0.029, DF = 1,008, t = -5.3; p < 0.001), and episodic memory (estimate = -0.08165, SE = 0.027, DF = 1,035, t = -2.92; p = 0.0036), but not with rate of decline in any cognitive domain. During follow-up, a larger increase in number of depression symptoms, was associated with worse cognitive outcomes in global cognition (estimate = -0.1053, SE = 0.027, DF = 1,612, t = -3.77; p = 0.0002), semantic categorization (estimate = -0.123, SE = 0.036, DF = 1,583, t = -3.36; p = 0.0008), and in episodic memory (estimate = -0.165, SE = 0.055, DF = 1,622, t = -3.02; p = 0.003), but the size of this effect was constant over time.

Conclusion: In elderly with T2D, increase in depression symptoms over time is associated with parallel cognitive decline, indicating that the natural course of the two conditions progresses concurrently and suggesting common underlying mechanisms".

Keywords: Trajectories; cognition; depression; older adults; type 2 diabetes.

Figure 1:. Associations of increase in depression symptoms with decrease in cognitive function over time

* Visual representation of Table 3; Model 2. The bars represent the size of the effect of every additional one-point increase in number of depression symptoms on change of z score, by cognitive domain and by time (18, 36 and 54 months after baseline). P-values ≤0.01 in the figure, represent a significant change in z score from baseline due to the one-point increase in GDS from baseline. For example, for global cognition, one-point increase in GDS from baseline to 18 months was associated with a significant decline of 0.095 in the z-score, whereas one-point increase in GDS from baseline to 36 months was associated with a significant decline of 0.084 in z score, and so forth. This is interpreted as follows: increases in number of depression symptoms were associated with changes in global cognition, but the extent of these changes over time remained similar (p=0.381 of the change and time interaction – see table 3).