Table 1.

Characteristics of participants at the end of the exposure period/beginning of outcome incidence follow-up for each data cycle used in the analyses of incident type 2 diabetes, defined using all available glycemic data and participant report of doctor-diagnosed diabetes^*

Characteristics	Cycle 1†	Cycle 2	Cycle 3	Cycle 4
Exposure period	1985–1988 to 1991–1994	1991–1994 to 1997–1999	1997–1999 to 2002–2004	2002–2004 to 2007–2009
Outcome follow-up period	1991–1994 to 1997–1999	1997–1999 to 2002–2004	2002–2004 to 2007–2009	2007–2009 to 2012–2013
Number of participants‡	5,545	4,117	3,878	4,238
Age (years), mean (SD)	49.8 (6.0)	55.4 (5.9)	60.6 (5.9)	65.2 (5.7)
Sex (% male)	71.2	71.3	72.7	73.9
Ethnicity (% white)	92.0	93.1	94.0	94.7
Employment grade (% low grade)	15.9	13.9	12.5	11.4
BMI (kg/m2), mean (SD)	24.4 (3.2)	25.0 (3.4)	25.9 (3.8)	26.2 (4.0)
Sleep duration at beginning of exposure period (%)
≤5 h	4.1	3.7	7.0	7.3
6 h	27.1	20.6	33.4	32.3
7 h	52.4	47.7	43.2	43.0
8 h	15.6	25.1	15.0	15.7
≥9 h	0.8	2.8	1.5	1.6
Sleep duration at end of exposure period (%)
≤5 h	4.0	7.3	7.7	7.3
6 h	21.0	32.9	32.3	29.2
7 h	46.8	43.3	42.6	42.3
8 h	25.4	15.0	15.8	19.4
≥9 h	2.9	1.5	1.7	1.8

*Definition of diabetes uses OGTT criteria or participant record of doctor-diagnosed diabetes for cycles 1 and 2, combined OGTT and HbA_1c criteria or participant record of doctor diagnosis for cycle 3, and combined fasting glucose and HbA_1c criteria or participant record of doctor diagnosis for cycle 4.

†Average sleep duration and change in sleep duration over the exposure period, years 1985–1988 to 1991–1994, and incident diabetes over the outcome follow-up period, 1991–1994 to 1997–1999.

‡Number of participants in the 2-h postload glucose and HbA_1c analyses differ slightly from those presented here.