Lung cancer risk and consumption of vegetables and fruit: an evaluation based on a systematic review of epidemiological evidence from Japan.

OBJECTIVE:
Clinical trials of β-carotene supplementation and recent large-scale prospective studies have called into question the protective effects of vegetable and fruit consumption against lung cancer. To re-assess this issue, we reviewed data from Japanese epidemiological studies.

METHODS:
Original data were obtained from searches of MEDLINE and the Japana Centra Revuo Medicina (Ichushi) database. The associations were assessed based on their magnitude and the strength of the evidence, together with their biological plausibility as previously evaluated by the International Agency for Research on Cancer.

RESULTS:
We identified six cohort studies and four case-control studies on the consumption of vegetables and/or fruit. We focused on fruit and green-yellow vegetables as food items, as they were included in more of the studies, and insufficient data were available on other types of vegetables. Among the three cohort and two case-control studies that reported on green-yellow vegetables, only one of each study type showed a weak inverse association between lung cancer risk and their consumption. Two of the four cohort studies and one (or possibly two) of the four case-control studies demonstrated a weak inverse correlation between lung cancer risk and fruit consumption. Meta-analysis for fruit consumption revealed a summary relative risk that was significantly smaller than unity.

CONCLUSIONS:
Our analysis of the Japanese epidemiological data showed that fruit consumption possibly decreased the risk of lung cancer, but found insufficient evidence of a link with vegetable consumption. Further prospective studies should assess the effects of consuming these food groups.