Table 3.

Relative Risks (95% CI) of Suicide According to Caffeine Consumption^a

	Caffeine Consumption (mg/day)
	≤100	100–250	250–400	400–550	≥550	P Value for Trend	Increment of 300 mg/day
NHS
No. of cases	8	19	8	5	7
Person-years	165,846	322,626	311,137	175,488	134,903
RR (95% CI)
Age-adjustedb	1.00	1.18 (0.51, 2.71)	0.50 (0.19, 1.34)	0.54 (0.18, 1.66)	0.86 (0.31, 2.39)	0.28	0.81 (0.52, 1.27)
Age, smoking-adjustedc	1.00	1.06 (0.46, 2.46)	0.41 (0.15, 1.10)	0.40 (0.13, 1.24)	0.51 (0.17, 1.47)	0.05	0.64 (0.41, 1.02)
Multivariated	1.00	0.99 (0.42, 2.31)	0.42 (0.15, 1.15)	0.46 (0.15, 1.45)	0.49 (0.17, 1.42)	0.06	0.66 (0.42, 1.04)
Sensitivitye	1.00	1.00 (0.43, 2.36)	0.32 (0.11, 0.93)	0.64 (0.22, 1.81)	0.46 (0.16, 1.34)	0.05	0.70 (0.45, 1.08)
NHS II
No. of cases	13	28	14	6	5
Person-years	390,687	373,038	270,719	117,755	97,821
RR (95% CI)
Age-adjustedb	1.00	2.19 (1.13, 4.23)	1.45 (0.68, 3.09)	1.42 (0.54, 3.75)	1.39 (0.49, 3.92)	0.85	1.05 (0.74, 1.51)
Age, smoking-adjustedc	1.00	1.92 (0.99, 3.73)	1.12 (0.52, 2.43)	0.94 (0.35, 2.53)	0.67 (0.23, 1.99)	0.16	0.77 (0.52, 1.12)
Multivariated	1.00	1.85 (0.95, 3.59)	1.05 (0.48, 2.27)	0.86 (0.32, 2.31)	0.61 (0.21, 1.80)	0.10	0.73 (0.50, 1.07)
Sensitivitye	1.00	1.71 (0.82, 3.57)	1.23 (0.54, 2.80)	1.08 (0.39, 3.00)	0.91 (0.32, 2.60)	0.52	0.87 (0.59, 1.28)
HPFS
No. of cases	62	49	35	6	12
Person-years	291,418	210,844	159,937	67,308	65,200
RR (95% CI)
Age-adjustedb	1.00	1.10 (0.75, 1.61)	1.06 (0.70, 1.62)	0.47 (0.20, 1.10)	0.93 (0.49, 1.74)	0.48	0.91 (0.72, 1.16)
Age, smoking- adjustedc	1.00	1.10 (0.75, 1.61)	1.02 (0.67, 1.56)	0.45 (0.19, 1.05)	0.74 (0.39, 1.40)	0.18	0.84 (0.66, 1.07)
Multivariated	1.00	1.06 (0.72, 1.56)	0.95 (0.62, 1.47)	0.41 (0.17, 0.97)	0.71 (0.37, 1.37)	0.12	0.82 (0.64, 1.05)
Sensitivitye	1.00	0.99 (0.66, 1.49)	1.13 (0.73, 1.76)	0.46 (0.20, 1.10)	0.60 (0.29, 1.25)	0.17	0.86 (0.67, 1.12)
Pooled resultsf
RR (95% CI)
Multivariated	1.00	1.20 (0.85, 1.69)	0.86 (0.57, 1.30)	0.54 (0.30, 0.94)	0.63 (0.39, 1.04)	0.005	0.77 (0.63, 0.93)
With NHS 1982–2008 follow-upg	1.00	1.07 (0.81, 1.42)	0.79 (0.58, 1.09)	0.45 (0.28, 0.73)	0.55 (0.36, 0.84)	<0.001	0.74 (0.63, 0.88)

Abbreviations: CI, confidence interval; HPFS, Health Professionals Follow-up Study; NHS, Nurses’ Health Study; RR, relative risk.

^aCaffeine was calculated from coffee and non-coffee sources (tea, caffeinated soft drink, chocolate). Cases of suicide were codes E950 to E959 according the Eight Revision International Classification of Diseases (ICD).

^bAdjusted for age (continuous), time interval and indicator variables for missing data on exposure for each questionnaire.

^cFurther adjusted for smoking status (never smoked, past, currently smoke 1–14, 15–24, or ≥25 cig./day).

^dFurther adjusted for high alcohol consumption (≥30 g/day, yes or no), body-mass index (<25, 25–29.9, ≥30 kg/m²), physical activity (quintiles), marital status (married/partnership, widowed, separated/divorced/single), and reported regular use of minor tranquilizers (yes or no), and antidepressants (yes or no). For women of NHS II, multivariate model was further adjusted for hormonal status (post-menopausal with or without hormonal therapy, pre-menopausal or never used hormonal therapy).

^eThe same as the multivariate model but using a latency of exposure of 4-year minimum. Number cases were as follow: 47 for NHS, 57 for NHS II, and 149 for HPFS.

^fResults from multivariate models were combined using random-effect model.

^gResults from multivariate models were combined using random-effect model, but follow-up was 1982 to June 2008 for NHS (cases=108).