Sleep disturbances and psychomotor retardation in the prediction of cognitive impairments in patients with major depressive disorder

Table 1 Demographic and clinical characteristics of patients with major depressive disorder, mean (SD)

Characteristics	MDD (n = 162)
Age (years)	35.1 (9.55)
Male/female	72/90
Education (years)	10.45 (3.41)
Age of onset (years)	31.94 (9.71)
Number of episodes (n)	2.15 (1.51)
Total illness duration (months)	40.36 (50.64)
HAM-D score	31.56 (7.28)
Retardation	8.08 (2.94)
Cognitive disturbances	4.73 (2.32)
Sleep disturbances	4.13 (1.98)
Anxiety/somatization	6.44 (2.31)
Weight loss	0.86 (0.79)
Diurnal variation	1.07 (0.82)
Hopelessness	6.25 (2.26)
HAM-A score	18.33 (6.31)
Psychic anxiety symptoms	12.47 (3.52)
Somatic anxiety symptoms	5.76 (3.49)

MDD: Major depressive disorder.

Table 2 Results of multiple linear regression analyses for the impact of depressive symptoms on different cognitive domains

		β	t	P value	R2	F	P value
Executive function	Retardation	-0.023	-0.850	0.396	0.096	20.31	0.029
	Cognitive disturbances	0.049	0.605	0.546
	Sleep disturbances	-0.235	-20.94	0.004
	Anxiety/somatization	0.076	0.901	0.369
	Weight loss	-0.017	-0.215	0.830
	Diurnal variation	-0.087	-10.10	0.273
	Hopelessness	-0.086	-0.959	0.339
Attention	Retardation	-0.01	-0.110	0.912	0.080	10.89	0.075
	Cognitive disturbances	0.113	10.37	0.172
	Sleep disturbances	-0.256	-30.17	0.002
	Anxiety/somatization	-0.028	-0.324	0.746
	Weight loss	-0.008	-0.102	0.919
	Diurnal variation	0.091	10.14	0.256
	Hopelessness	-0.053	-0.585	0.560
Processing speed	Retardation	-0.218	-20.37	0.019	0.095	20.30	0.029
	Cognitive disturbances	-0.006	-0.076	0.940
	Sleep disturbances	-0.160	-20.00	0.047
	Anxiety/somatization	-0.036	-0.428	0.670
	Weight loss	-0.001	-0.015	0.988
	Diurnal variation	0.083	10.05	0.297
	Hopelessness	0.001	0.007	0.995
Memory	Retardation	-0.113	-10.27	0.207	0.165	30.77	< 0.001
	Cognitive disturbances	0.067	0.843	0.401
	Sleep disturbances	-0.352	-40.52	< 0.001
	Anxiety/somatization	-0.045	-0.546	0.586
	Weight loss	0.052	0.670	0.504
	Diurnal variation	-0.062	-0.334	0.739
	Hopelessness	0.047	0.542	0.589

Table 3 Simple mediation analysis for the relationship between sleep disturbances and processing speed

Mediating variable (M)	Independent variable (X)	Dependent variable (Y)	X→M	M→Y	Indirect effect1	Direct effect1
Retardation	Sleep disturbances	Processing speed	0.204a	-0.105b	-0.021 [-0.051, -0.002]1	-0.075 [-0.150, 0.0001]

^aP < 0.05.

^bP < 0.01.

¹Significant point estimates (P < 0.05) as determined by the exclusion of zero from the confidence interval.

Table 4 Results of multiple linear regression analysis for the effect of anxiety symptoms on different cognitive domains

		β	t	P value	R2	F	P value
Executive function	HAMA-psychic symptoms	-0.343	-30.67	< 0.001	0.081	60.84	< 0.001
	HAMA-somatic symptoms	0.158	10.69	0.094
Attention	HAMA-psychic symptoms	-0.278	-20.96	0.004	0.053	40.41	0.014
	HAMA-somatic symptoms	0.140	10.48	0.140
Processing speed	HAMA-psychic symptoms	-0.215	-20.27	0.025	0.040	30.32	0.039
	HAMA-somatic symptoms	-0.027	0.282	0.778
Memory	HAMA-psychic symptoms	-0.238	-20.54	0.012	0.060	50.03	0.008
	HAMA-somatic symptoms	-0.011	-0.116	0.908

Table 5 Simple mediation analysis for the relationship between psychic anxiety symptoms and cognitive performance

Mediating variable (M)	Independent variable (X)	Dependent variable (Y)	X→M	M→Y	Indirect effect1	Direct effect1
Sleep disturbances	HAMA-psychic symptoms	Executive function	0.285c	-0.048	-0.013 [-0.027, -0.001]1	-0.027 [-0.054, 0.001]
Sleep disturbances	HAMA-psychic symptoms	Processing speed	0.285c	-0.063	-0.018 [-0.042, 0.007]	-0.037 [-0.086, 0.012]
Sleep disturbances	HAMA-psychic symptoms	Memory	0.285c	-0.522c	-0.149 [-0.237, -0.063]1	-0.075 [-0.232, 0.081]
Retardation	HAMA-psychic symptoms	Processing speed	0.241c	-0.097a	-0.023 [-0.045, -0.004]1	-0.031 [-0.077, 0.014]

^aP < 0.05.

^cP < 0.001.

¹Significant point estimates (P < 0.05) as determined by the exclusion of zero from the confidence interval.