Table 1.
Modification of the effect of β-carotene on mortality by the level of smoking and the age of smoking initiation (Alpha-Tocopherol Beta-Carotene Study 1985–1993)*
(Numbers of participants; risk ratios (RR) and 95 % confidence intervals)
| Smoking at study baseline (cigarettes/d) | Age of smoking initiation | |||||||
|---|---|---|---|---|---|---|---|---|
| ≤20 years (median 18 years) | ≥21 years (median 24 years) | |||||||
| Placebo | β-Carotene | RR | 95 % CI | Placebo | β-Carotene | RR | 95 % CI | |
| 5–20 (median 16) | ||||||||
| Deaths | 428 | 445 | 1·03 | 0·90, 1·18 | 147 | 165 | 1·12 | 0·90, 1·40 |
| Participants | 3550 | 3555 | 1336 | 1365 | ||||
| 21–90 (median 30) | ||||||||
| Deaths | 232 | 248 | 1·09 | 0·91, 1·30 | 43 | 62 | 1·56 | 1·06, 2·3 |
| Participants | 1892 | 1876 | 506 | 484 | ||||
This Table is restricted to the 14 564 no-vitamin E participants. Adding a uniform β-carotene effect gave a RR of 1·088 (95 % CI 0·99, 1·20). Adding an individual β-carotene effect, shown in this Table, to each of the four subgroups non-significantly improved the fit of the Cox regression model (χ2 (3 df) = 4·2; P = 0·24). Within the subgroup of the heavy smokers (≥21/d) who started smoking late in their life (≥21 years), in the lower right-hand corner, the difference between the β-carotene and placebo arms was significant (P = 0·024; see Fig. 1).