Despite the unexpected results from the
beta-Carotene and
Retinol Efficacy Trial (CARET) and similar supplementation trials showing that supplementation with
beta-carotene increased, rather than decreased,
lung cancer incidence, considerable interest remains in investigating how other compounds in fruits and vegetables may affect
lung cancer risk. We used data from 14,120 CARET participants who completed food frequency questionnaires to examine associations of diet with
lung cancer risk. After 12 years of follow-up (1989-2001), 742 participants developed
lung cancer. We used Cox proportional hazards models to estimate multivariate relative risks (RRs) and 95% confidence intervals (CIs). Analyses were controlled for smoking,
asbestos exposure, and other covariates. Analyses of specific botanical groups were also controlled for total fruit and vegetable intake. All models were stratified by CARET treatment arm, and all statistical tests were two-sided. Statistically significant associations of fruit and vegetable intake with lower
lung cancer risk were restricted to the CARET placebo arm. The RR for highest versus lowest quintile of total fruit consumption in the placebo arm was 0.56 (95% CI, 0.39-0.81) with a two-sided P for trend = 0.003. Two specific botanical groups were associated with reduced risk of
lung cancer. Compared with the lowest quintile of rosaceae fruit consumption, placebo participants in the top quintile had a RR of 0.63 (95% CI, 0.42-0.94; P for trend = 0.02); for cruciferae vegetables, the RR was 0.68 (95% CI, 0.45-1.04; P for trend = 0.01). We did not observe any statistically significant associations of fruit and vegetable intake with
lung cancer risk among participants randomized to receive the CARET supplements (30 mg of
beta-carotene and 25,000 IU of
retinyl palmitate). This report provides evidence that plant foods have an important preventive influence in a population at high risk for
lung cancer. However, persons who use
beta-carotene supplements do not benefit from the protective compounds in plant foods.