. 2013 Jun 25;178(6):956–961. doi: 10.1093/aje/kwt072

Table 1.

Association Between Sleep Duration, Assessed in 1997/1999, and Average C-reactive Protein and Interleukin-6, Assessed in 1997/1999 and 2002/2004 Using Data From the Whitehall II Study

Sleep Duration, hours	C-reactive Protein (mg/L)
Sleep Duration, hours	No.	Mean^a	95% CI
Total	4,972
≤5	365	1.47	1.32, 1.64
6	1,638	1.30*	1.23, 1.36
7	2,149	1.28*	1.22, 1.34
8	747	1.20**	1.11, 1.29
≥9	73	1.31	1.03, 1.66
P_{heterogeneity}		0.05
	Interleukin-6 (µg/L)
	No.	Mean^a	95% CI
Total	4,689
≤5	339	1.85	1.75, 1.96
6	1,558	1.75	1.71, 1.80
7	2,027	1.70**	1.67, 1.74
8	698	1.69**	1.62, 1.75
≥9	67	1.74	1.54, 1.97
P_{heterogeneity}		0.04

Abbreviation: CI, confidence interval.

* P < 0.05; **P < 0.01 (difference relative to ≤5 hours, arbitrary reference category).

^a Values are geometric means adjusted for age, sex, and occupational position.