The association between cortisol:C-reactive protein ratio and depressive fatigue is a function of CRP rather than cortisol

Figures & data

Table 1 Distributions of all dependent variables

Variable	Mean	SD	Range
SDS total score	38.54	7.25	24–57
SDS item 10	1.78	0.89	1–4
CRP mg/L	4.86	6.81	0.83–69.85
CRP log	0.55	0.30	−0.08 to 1.84
Cortisol nmol/L	20.22	8.46	2.40–34.30
Cortisol log	1.25	0.23	0.38–1.54
Cortisol:CRP ratio	7.40	6.17	0.05–33.79
Cortisol:CRP ratio log	0.70	0.44	−1.28 to 1.53
Cortisol:CRP ratio log quartile 1 (n=31)	0.12	0.36	−1.28 to 0.49
Cortisol:CRP ratio log quartiles 2 & 3 (n=69)	0.78	0.15	0.50–1.02
Cortisol:CRP ratio log quartile 4 (n=26)	1.21	0.14	1.03–1.53

Abbreviations: SDS, self-rating depression scale; CRP, C-reactive protein.

Table 2 Pearson correlation coefficients between variables

Variable	Cortisol log	CRP log	Cortisol:CRP log	SDS total score
Cortisol log
CRP log	−0.308***
Cortisol:CRP log	0.747***	−0.863***
SDS total score	0.045	0.005	0.020
SDS item 10	−0.115	0.283**	−0.260*	0.503***

Notes: *p= 0.005, **p= 0.002, ***p< 0.001.

Abbreviations: SDS, self-rating depression scale; CRP, C-reactive protein.

Table 3 Univariate effects for MANOVA on first vs third cortisol:CRP log quartiles

Variable	Quartile 1 M (SD)	Quartile 3 M (SD)	F	p	Partial eta squared
Cortisol (nmol/L)	11.00 (5.16)	26.53 (5.50)	107.621	<0.001	0.687
CRP (mg/L)	10.32 (12.73)	1.64 (0.57)	10.615	0.002	0.178
Cortisol:CRP ratio log	0.12 (0.37)	1.23 (0.13)	177.289	<0.001	0.783
SDS total score	38.57 (7.53)	39.04 (6.59)	0.055	0.815	0.001
SDS item 10 score	2.14 (1.07)	1.61 (0.58)	4.543	0.038	0.085

Abbreviations: SDS, self-rating depression scale; CRP, C-reactive protein.