Table 4.
Relative Risks (95% CI) of Suicide According to Decaffeinated Coffee Consumptiona
| Decaffeinated Coffee Consumption (cups) | ||||||
|---|---|---|---|---|---|---|
|
| ||||||
| ≤1/week | 2–6/week | 1/day | ≥2/day | P Value for Trend | Increment of 1 cup/day | |
| NHS | ||||||
| No. of cases | 26 | 8 | 11 | 2 | ||
| Person-years | 468,072 | 369,499 | 202,131 | 70,299 | ||
| RR (95% CI) | ||||||
| Age-adjustedb | 1.00 | 0.52 (0.23, 1.18) | 1.24 (0.59, 2.61) | 0.52 (0.12, 2.21) | 0.96 | 1.06 (0.78, 1.44) |
| Age, smoking-adjustedc | 1.00 | 0.57 (0.25, 1.31) | 1.25 (0.59, 2.68) | 0.47 (0.11, 1.99) | 0.82 | 1.01 (0.74, 1.37) |
| Multivariated | 1.00 | 0.55 (0.23, 1.30) | 1.29 (0.59, 2.79) | 0.54 (0.12, 2.33) | 0.99 | 1.04 (0.76, 1.43) |
| Sensitivitye | 1.00 | 0.56 (0.24, 1.31) | 1.07 (0.47, 2.45) | 0.70 (0.21, 2.40) | 0.91 | 1.02 (0.74, 1.39) |
| NHS II | ||||||
| No. of cases | 41 | 20 | 2 | 3 | ||
| Person-years | 777,390 | 323,200 | 101,075 | 48,355 | ||
| RR (95% CI) | ||||||
| Age-adjustedb | 1.00 | 1.13 (0.66, 1.94) | 0.35 (0.08, 1.43) | 1.05 (0.32, 3.43) | 0.53 | 0.93 (0.63, 1.35) |
| Age, smoking-adjustedc | 1.00 | 1.28 (0.74, 2.19) | 0.36 (0.09, 1.50) | 0.96 (0.29, 3.14) | 0.47 | 0.91 (0.63, 1.31) |
| Multivariated | 1.00 | 1.29 (0.75, 2.23) | 0.37 (0.09, 1.55) | 0.97 (0.29, 3.19) | 0.49 | 0.91 (0.63, 1.31) |
| Sensitivitye | 1.00 | 1.10 (0.60, 2.03) | 0.42 (0.10, 1.74) | 1.08 (0.33, 3.58) | 0.69 | 1.03 (0.73, 1.45) |
| HPFS | ||||||
| No. of cases | 89 | 41 | 24 | 10 | ||
| Person-years | 361,414 | 257,832 | 106,582 | 68,878 | ||
| RR (95% CI) | ||||||
| Age-adjustedb | 1.00 | 0.62 (0.42, 0.90) | 0.90 (0.57, 1.43) | 0.55 (0.29, 1.08) | 0.23 | 0.87 (0.72, 1.05) |
| Age, smoking- adjustedc | 1.00 | 0.61 (0.42, 0.90) | 0.90 (0.56, 1.44) | 0.53 (0.27, 1.03) | 0.19 | 0.86 (0.71, 1.04) |
| Multivariated | 1.00 | 0.64 (0.43, 0.94) | 0.95 (0.59, 1.54) | 0.57 (0.29, 1.12) | 0.28 | 0.89 (0.73, 1.07) |
| Sensitivitye | 1.00 | 0.66 (0.44, 0.99) | 1.03 (0.63, 1.68) | 0.56 (0.28, 1.11) | 0.29 | 0.88 (0.73, 1.06) |
| Pooled resultsf | ||||||
| RR (95% CI) | ||||||
| Multivariated | 1.00 | 0.79 (0.47, 1.32) | 0.95 (0.61, 1.48) | 0.63 (0.37, 1.09) | 0.26 | 0.92 (0.80, 1.07) |
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 cup of caffeinated coffee (continuous, cup/day), 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, 66 for NHS II, and 164 for HPFS.
Results from multivariate models were combined using random-effect model.