The serotonin transporter polymorphism (5-HTTLPR) and cortisol stress responsiveness: preliminary evidence for a modulating role for sleep quality

Figures & data

Table 1. Sample characteristics M (SD).

			t-test
	S’/S’	L’/L’	t(48)	p
N	25	25
Men	5	5
Women	20	20
Age	23.9 (1.7)	24.0 (2.2)	0.215	.831
PSQI	2.9 (1.4)	2.9 (1.7)	0.090	.929
BDI	2.9 (2.4)	2.5 (3.1)	−0.507	.615

BDI: Beck Depression Inventory; M: mean; n: number of participants; p: p value; PSQI: Pittsburgh Sleep Quality Index.

Table 2. Cortisol values (nmol/L).

	S’/S’		L’/L’		t-test
	M	SD	M	SD	t(48)	p
Baseline	6.73	2.22	8.48	3.41	2.147	.038
Pre-stress	6.42	1.83	7.48	2.34	1.774	.082
Post-stress	12.61	4.86	12.47	4.79	−0.103	.919
Recovery	13.57	6.70	13.29	7.32	−0.139	.890
Increment	6.18	4.60	4.99	3.97	−0.984	.330
AUCg	29.18	9.15	30.83	10.25	0.600	.551
AUCi	8.98	8.14	5.39	8.22	−1.551	.127

AUCg: area under the curve ground; AUCi: area under the curve increase; M: mean; n: number of participants; p: p value.

Figure 1. Stress-related change in salivary cortisol (AUCi) as a function of sleep quality in S’/S’ and L’/L’ 5-HTTLPR genotype. Interaction: p < .01.

Table 3. Summary of hierarchical regression analysis for variables predicting AUCi.

	Model 1			Model 2			Model 3
	B	SE B	β	B	SE B	β	B	SE B	β
Genotype
S’/S’ vs. L’/L’	3.59	2.31	.22	3.62	2.32	.22	15.83	4.63	.96**
Sleep Quality				0.71	0.75	.13	2.44	0.91	.46*
Genotype × Sleep Quality
S’/S’ vs. L’/L’ × Sleep Quality							−4.22	1.42	−.90**
R^2	0.05			0.07			0.22*
F(ΔR^2)	2.41			0.88			8.87**

Allelic variation within 5-HTTLPR is represented by the variable “Genotype” coded in the regression model as S’/S’ (1) and L’/L’ (0).

* p < .05.

** p < .01.

Figure 2. Mean (±SEM) cortisol levels as a function of 5-HTTLPR genotype in individuals reporting high (PSQI ≤3) or low (PSQI ≥4) sleep quality.