Table 2.
Relative Risks (95% CI) of Suicide According to Caffeinated Coffee Consumptiona
| Caffeinated Coffee Consumption (cups) | |||||||
|---|---|---|---|---|---|---|---|
|
| |||||||
| ≤1/week | 2–6/week | 1/day | 2–3/day | ≥4/day | P Value for Trend | Increment of 2 cups/day | |
| NHS | |||||||
| No. of cases | 16 | 5 | 14 | 8 | 4 | ||
| Person-years | 257,634 | 134,745 | 349,735 | 294,138 | 73,749 | ||
| RR (95% CI) | |||||||
| Age-adjustedb | 1.00 | 0.63 (0.23, 1.73) | 0.69 (0.33, 1.42) | 0.40 (0.17, 0.95) | 0.67 (0.22, 2.03) | 0.19 | 0.81 (0.54, 1.21) |
| Age, smoking- adjustedc | 1.00 | 0.60 (0.22, 1.66) | 0.60 (0.29, 1.25) | 0.30 (0.12, 0.71) | 0.38 (0.12, 1.20) | 0.03 | 0.66 (0.44, 0.99) |
| Multivariated | 1.00 | 0.67 (0.24, 1.88) | 0.62 (0.29, 1.31) | 0.35 (0.14, 0.85) | 0.35 (0.11, 1.13) | 0.03 | 0.67 (0.45, 1.01) |
| Sensitivitye | 1.00 | 0.68 (0.24, 1.92) | 0.57 (0.26, 1.24) | 0.43 (0.19, 0.99) | 0.34 (0.10, 1.08) | 0.04 | 0.70 (0.47, 1.04) |
| NHS II | |||||||
| No. of cases | 24 | 10 | 19 | 9 | 4 | ||
| Person-years | 532,352 | 125,576 | 244,623 | 276,714 | 70,755 | ||
| RR (95% CI) | |||||||
| Age-adjustedb | 1.00 | 1.74 (0.83, 3.65) | 1.64 (0.89, 3.01) | 0.67 (0.31, 1.45) | 1.11 (0.38, 3.24) | 0.45 | 0.99 (0.71, 1.39) |
| Age, smoking- adjustedc | 1.00 | 1.68 (0.80, 3.52) | 1.43 (0.77, 2.64) | 0.49 (0.22, 1.07) | 0.53 (0.18, 1.61) | 0.03 | 0.76 (0.54, 1.08) |
| Multivariated | 1.00 | 1.63 (0.77, 3.42) | 1.38 (0.74, 2.57) | 0.46 (0.21, 1.01) | 0.55 (0.18, 1.65) | 0.03 | 0.74 (0.52, 1.06) |
| Sensitivitye | 1.00 | 1.63 (0.71, 3.72) | 1.64 (0.84, 3.18) | 0.44 (0.18, 1.07) | 0.81 (0.29, 2.26) | 0.11 | 0.86 (0.60, 1.23) |
| HPFS | |||||||
| No. of cases | 73 | 22 | 32 | 29 | 8 | ||
| Person-years | 306,247 | 105,251 | 168,482 | 163,560 | 51,166 | ||
| RR (95% CI) | |||||||
| Age-adjustedb | 1.00 | 0.82 (0.51, 1.34) | 0.79 (0.52, 1.21) | 0.78 (0.50, 1.21) | 0.67 (0.32, 1.40) | 0.18 | 0.88 (0.70, 1.11) |
| Age, smoking-adjustedc | 1.00 | 0.81 (0.49, 1.31) | 0.76 (0.50, 1.17) | 0.72 (0.46, 1.12) | 0.50 (0.24, 1.07) | 0.04 | 0.81 (0.64, 1.02) |
| Multivariated | 1.00 | 0.81 (0.49, 1.32) | 0.74 (0.48, 1.15) | 0.65 (0.41, 1.03) | 0.49 (0.23, 1.06) | 0.02 | 0.79 (0.62, 1.00) |
| Sensitivitye | 1.00 | 0.89 (0.53, 1.48) | 0.77 (0.48, 1.23) | 0.86 (0.55, 1.35) | 0.44 (0.18, 1.04) | 0.09 | 0.83 (0.65, 1.06) |
| Pooled resultsf | |||||||
| RR (95% CI) | |||||||
| Multivariated | 1.00 | 0.97 (0.59, 1.58) | 0.86 (0.55, 1.34) | 0.55 (0.38, 0.78) | 0.47 (0.27, 0.81) | <0.001 | 0.75 (0.63, 0.90) |
| With NHS 1982–2008 follow-upg | 1.00 | 0.93 (0.65, 1.33) | 0.86 (0.64, 1.15) | 0.51 (0.37, 0.70) | 0.47 (0.30, 0.75) | <0.001 | 0.74 (0.63, 0.86) |
Abbreviations: CI, confidence interval; HPFS, Health Professionals Follow-up Study; NHS, Nurses’ Health Study; RR, relative risk.
Cases of suicide were codes E950 to E959 according the Eight Revision International Classification of Diseases (ICD).
Adjusted for age (continuous), time interval and indicator variables for missing data on exposure for each questionnaire.
Further adjusted for smoking status (never smoked, past, currently smoke 1–14, 15–24, or ≥25 cig./day).
Further 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).
The 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.
Results from multivariate models were combined using random-effect model.
Results from multivariate models were combined using random-effect model, but the follow-up was 1982 to June 2008 for NHS (cases=108).