Table 1.

Baseline Characteristics of Study Participants According to Quintile of Caffeine Intake, National Institutes of Health-AARP Diet and Health Study, 1995–2006

	Quintile of Caffeine Intake
	1 (<17.4 mg/day) (n = 60,980)		2 (17.4–<129.2 mg/day) (n = 61,010)		3 (129.2–<510.9 mg/day) (n = 60,985)		4 (510.9–<589.8 mg/day) (n = 61,009)		5 (≥589.8 mg/day) (n = 60,996)
	%	Median (IQRa) or Mean (SD)	%	Median (IQR) or Mean (SD)	%	Median (IQR) or Mean (SD)	%	Mean (SD) or Median (IQR)	%	Median (IQR) or Mean (SD)
Median caffeine intake, mg/day		7.8 (8.4)		45.3 (50.8)		232.9 (90.8)		538.2 (30.6)		946.4 (357.6)
Mean age, years		61.9 (5.3)		61.5 (5.3)		61.5 (5.4)		61.6 (5.3)		60.6 (5.3)
Male gender	51.8		59.6		52.2		61.6		67.9
Race
Non-Hispanic white	90.6		92.1		90.5		94.6		95.3
Other	8.3		6.9		8.3		4.6		3.7
Missing data	1.2		1.0		1.2		0.9		1.0
Smoking status
Never smoker	47.6		42.1		42.8		32.7		26.2
Past smoker
Smoked for 1–9 years	12.4		11.8		11.8		12.5		11.0
Smoked for 10–29 years	20.2		22.2		21.2		24.8		23.0
Smoked for ≥30 years	10.2		12.0		11.8		14.9		15.8
Missing data on duration of past smoking	3.9		3.8		3.8		3.6		3.4
Current smoker	4.5		6.8		7.4		10.3		19.3
Missing data	1.2		1.2		1.2		1.2		1.3
Frequency of physical activity
Never or rarely	13.8		15.1		16.8		15.0		17.2
1–3 times/month	11.5		13.3		14.0		13.9		14.8
1–2 times/week	19.8		22.3		22.0		22.9		23.2
3–4 times/week	30.3		28.6		27.1		28.4		25.8
≥5 times/week	23.7		19.9		19.3		19.2		18.4
Missing data	0.9		0.8		0.9		0.7		0.7
Hormone use (women only)b
Premenopausal	1.9		2.3		1.9		2.0		2.0
Postmenopausal
Never user	40.6		39.6		41.8		40.2		45.7
User	52.3		52.9		51.2		53.1		47.8
Inconsistent user	4.3		4.3		4.2		4.0		3.7
Missing data	1.0		0.9		0.9		0.7		0.7

Abbreviations: IQR, interquartile range; SD, standard deviation.

^a25th–75th percentiles.

^bNumbers of female participants—quintile 1: 29,369; quintile 2: 24,637; quintile 3: 29,171; quintile 4: 23,429; quintile 5: 19,606.