Table 2. Results of correlation and multivariable regression analyses of demographical and clinical characteristics with serum levels of BDNF in antidepressant free patients with MDD.

	ra	B	95% CI B	β	t	P-value
Gender (1=male, 2=female)	−0.13**	−0.65	−1.24 to −0.06	−0.10	−2.15	0.03
Age (continuous, years)	0.17**	0.03	0.01 to 0.06	0.11	1.98	0.04
Education (continuous, years)	−0.04	−0.01	−0.09 to 0.08	−0.005	−0.11	0.91
BMI (continuous)	0.13**	0.06	0.01 to 0.10	0.09	1.97	0.04
Met-minutes (continuous, IPAQ)	−0.02	−0.001	−0.01 to 0.01	−0.009	−0.21	0.83
Smoker (1=no, 2=yes)	−0.02	−0.07	−0.04 to 0.02	−0.02	−0.44	0.66
Time of Blood withdrawal (continuous)b	−0.04	−0.004	−0.12 to 0.02	−0.04	−1.11	0.23
Duration of serum storage (continuous, days)	0.02	0.14	−0.40 to 0.68	0.02	0.49	0.62
MDD status (1=current, 2=early remitted)c	−0.11*	−0.15	−0.50 to 0.25	−0.04	−0.64	0.52
MDD severity (continuous, IDS)	0.03	−0.007	−0.04 to 0.02	−0.06	−1.12	0.24
MDD type (1=single episode, 2=recurrent)	0.01	0.05	−0.56 to 0.66	0.007	0.15	0.88
Comorbid anxiety disorder (1=no, 2=yes)	0.08*	0.31	−0.36 to 0.97	0.05	0.91	0.36
Age at onset MDD (continuous)	0.14**	0.08	−0.04 to 0.18	0.07	1.25	0.21
Chronic MDD (1=no, 2=yes)	0.07	0.19	−0.49 to 0.87	0.03	0.55	0.58
Suicide ideation (1=no, 2=yes)	0.06	0.59	−0.13 to 1.33	0.07	1.51	0.12

Abbreviations: BDNF, brain-derived neurotrophic factor; BMI, body mass index; CI, confidence interval; IDS, inventory of depressive symptoms; IPAQ, international physical activity questionnaire; MDD, major depressive disorder.

^*Denotes statistical significance of the univariate correlation at P<0.05.

^**Denotes statistical significance of the univariate correlation at P<0.01.

^aUnivariate correlation with serum levels of BDNF; Pearson's r for continuous variables and Spearman's ρ for variables.

^bIn minutes from 0600 hours.

^cThe presence of a current (1 month) versus an early remission (1–6 months of remission) diagnosis.