Severe depression is associated with decreased levels of serum brain-derived neurotrophic factor in type 2 diabetes patients in Ghana

Figures & data

Table 1. General characteristics of the study participants.

	T2DM patients (n = 200)	Non-diabetes (n = 160)	p
Demographical parameters
Gender, n (%)			0.404
Male	76 (38)	54 (33.8)
Female	124 (62)	106 (66.2)
Age, yrs (range)	52 ± 7.9 (30–69)	48.6 ± 10.6 (31–67)	<0.001
Age decades, n (%)			0.001
<40	20 (10)	38 (23.7)
40–49	42 (21)	40 (25)
50–59	108 (54)	64 (40)
60+	30 (15)	18 (11.3)
Married	113 (56.5)	98 (61.3)	0.363
Living with relatives	139 (69.5)	109 (68.1)	0.779
Educational levels, n (%)			0.005
None	16 (8)	18 (11.3)
Junior high school	108 (54)	60 (37.5)
Senior high school	54 (27)	68 (42.5)
Tertiary	22 (11)	14 (8.8)
Employment, n (%)			0.021
Formal	69 (39.5)	78 (48.8)
Self-employed	98 (49)	64 (40)
Unemployed	33 (16.5)	18 (11.2)
Clinical parameters
PHQ-9 score	7.9 ± 5.7	5.1 ± 3.8	<0.001
PHQ-9 score > 9, n (%)	63 (31.5)	17 (10.6)	<0.001
Alcohol intake, n (%)	86 (42)	46 (28.8)	0.005
Previous smoker, n (%)	74 (37)	15 (9.4)	<0.001
Hypertension, n (%)	132 (66)	16 (10)	<0.001
BMI, kg/m^2	30.8 ± 7.1	25.9 ± 5.9	<0.001
Systolic BP, mmHg	145 ± 27	133 ± 11	<0.001
Diastolic BP, mmHg	89 ± 19	82 ± 14	<0.001
Mean BP, mmHg	117 ± 13	111 ± 10	<0.001
Pulse BP, mmHg	61 ± 12	52 ± 11	<0.001
Heart rate, beats/min	72 ± 16	67 ± 8	<0.001
Biochemical parameters
Fasting plasma glucose mmol/l	7.8 ± 3.5	5.1 ± 0.8	<0.001
Total cholesterol, mmol/l	5.6 ± 1.2	3.9 ± 1.1	<0.001
Triglycerides, mmol/l	2.4 ± 1.1	1.4 ± 0.8	<0.001
HDL cholesterol, mmol/l	1.1 ± 0.5	1.4 ± 0.4	<0.001
LDL cholesterol, mmol/l	2.3 ± 1.1	2 ± 1.2	0.015
BDNF, ng/ml	22.8 ± 4.6	34.6 ± 10.6	<0.001

SHS, senior high school; BMI, body mass index; BP, blood pressure; PHQ, Patient’s Health Questionnaire; BDNF, brain-derived neurotrophic factor; HDL, high-density lipoprotein; LDL, low-density lipoprotein.

Figure 1. Severity of depression in study participants.

Figure 2. Serum levels of BDNF among study participants by diabetes and depression status. Depression is defined as a PHQ-9 score >10.

Table 2. Correlation between serum BDNF levels and participant characteristics.

	All participants		T2DM patients		Non-diabetic controls
	r	p	r	p	r	p
Age	−0.26	<0.001	−0.17	0.021	−0.13	0.101
T2DM duration			−0.14	0.065
BMI	0.08	0.449	0.11	0.258	−0.17	0.192
Systolic BP	−0.19	0.001	−0.21	0.003	0.25	0.033
FPG	−0.12	0.112	−0.16	0.031	−0.06	0.439
Triglycerides	−0.32	<0.001	−0.21	0.032	−0.15	0.208
Total cholesterol	0.18	0.002	0.17	0.038	0.09	0.344
HDL cholesterol	0.19	0.001	0.1	0.118	0.38	<0.001
LDL cholesterol	−0.17	0.004	0.15	0.044	−0.03	0.668

T2DM, type 2 diabetes; BMI, body mass index; BP, blood pressure; FPG, fasting plasma glucose; HDL, high-density lipoprotein; LDL, low-density lipoprotein.

Table 3. Associated between serum BDNF and levels of depression from logistic regression models.

	Unadjusted model		Adjusted model
	OR (95% CI)	p	OR (95% CI)	p
All participants
Mild depression	0.92 (0.61–1.15)	0.197	0.97 (0.42–1.37)	0.368
Moderate depression	0.83 (0.59–1.02)	0.053	0.91 (0.58–1.43)	0.406
Severe depression	0.79 (0.52–0.94)	0.024	0.85 (0.49–0.97)	0.033
T2DM patients
Mild depression	0.67 (0.36–1.12)	0.138	0.74 (0.51–1.15)	0.177
Moderate depression	0.99 (0.77–1.95)	0.374	0.9 (0.72–1.84)	0.362
Severe depression	0.76 (0.63–0.93)	0.031	0.81 (0.57–0.97)	0.042
Non-diabetic controls
Mild depression	0.77 (0.54–0.92)	<0.001	0.84 (0.6–0.95)	<0.001
Moderate depression	1.09 (0.91–1.72)	0.317	1.55 (0.95–2.07)	0.726

Multivariable models were adjusted for age, gender, BMI, diabetes status (for all participants), hypertension, previous smoking, alcohol intake, marital status, education levels, employment, triglycerides, and total and HDL cholesterol.Other significant variables in the multivariable-adjusted models were:All participants: T2DM [0.7 (0.38–0.98), p = 0.042]; previous smoking [0.82 (0.47–0.91), p = 0.039]; total cholesterol [1.86 (1.18–3.14), p = 0.004] and triglycerides [0.58 (0.19–0.93), p<0.001].T2DM patients: insulin treatment [0.83 (0.47–0.98), p = 0.027]; previous smoking [0.86 (0.41–0.97), p = 0.005] and total cholesterol [0.89 (0.63–0.95), p = 0.042].Non-diabetic controls: Female gender [0.68 (0.21–0.89), p<0.001]; alcohol intake [0.73 (0.39–0.91), p<0.001]; hypertension [0.79 (0.45–0.93), p<0.001]; total cholesterol [1.19 (1.03–1.22), p = 0.045]; triglycerides [1.22 (1.09–1.31), p = 0.024] and HDL cholesterol [1.97 (1.11–3.06), p<0.001]. Statistical notes: In multivariable regression analyses, marital status, education levels, and employment were removed from the models due to high collinearity and valence inflation factor that affected the model diagnostics. In non-diabetic controls, previous smoking status and BMI also affected the model diagnosis and hence, they were removed from the model.

Table 4. Predictors of serum BDNF levels in study participants from multiple regression analysis.

	All participants			T2DM patients			Non-diabetic controls
	B±SE	β	p	B±SE	β	p	B±SE	β	p
Depression (reference: No depression)
Mild	−2.8 ± 3.11	−0.29	0.37	−5.57 ± 4.1	−0.57	0.179	−3.73 ± 0.45	−0.78	<0.001
Moderate	−2.76 ± 3.29	−0.29	0.404	−3.47 ± 3.77	−0.35	0.36	0.31 ± 0.89	0.06	0.728
Severe	−8.25 ± 3.73	−0.86	0.031	−8.13 ± 4.13	−0.83	0.043
T2DM	−4.5 ± 2.7	−0.51	0.044
Insulin treatment				−2.91 ± 0.96	−1.56	0.024
Age	−0.16 ± 0.1	−0.19	0.109	−0.31 ± 0.21	−0.2	0.138	−0.02 ± 0.02	−0.03	0.495
Females	0.38 ± 3	0.04	0.9	−7.55 ± 4.51	−0.77	0.099	−5.46 ± 0.67	−1.14	<0.001
Previous smoking	−12.48 ± 6.75	−1.4	0.038	−19.66 ± 6.93	−2.01	0.006
Alcohol	3.29 ± 3.02	0.37	0.28	−2.89 ± 3.77	−0.3	0.446	−23.66 ± 1.43	−4.92	<0.001
Hypertension	−3.03 ± 1.83	−0.34	0.101	−1.89 ± 2.97	−0.19	0.527	−11.17 ± 0.78	−2.32	<0.001
BMI	0.17 ± 0.12	0.13	0.161	0.05 ± 0.19	0.03	0.813
Total cholesterol	2.75 ± 0.97	0.28	0.005	−2.43 ± 1.16	−0.25	0.04	0.48 ± 0.24	0.17	0.046
Triglycerides	−3.26 ± 0.8	−0.45	<0.001	−1.37 ± 0.98	−0.18	0.166	1.26 ± 0.54	0.11	0.022
HDL cholesterol	1.52 ± 2.01	0.08	0.451	−0.92 ± 2.72	−0.05	0.737	11.75 ± 0.89	0.98	<0.001

T2DM, type 2 diabetes patients; BMI, body mass index; B, estimate from regression model; β, standardized estimate from the regression model.

Statistical notes: Marital status, education levels, and employment were removed from the models due to high collinearity and valence inflation factor that affected the model diagnostics. In non-diabetic controls, previous smoking status and BMI also affected the model diagnosis and hence, they were removed from the model.