Isoflavone intake and risk of lung cancer: a prospective cohort study in Japan.
BACKGROUND
Although case-control studies support the idea that soy foods or isoflavone intake is associated with a decreased risk of lung cancer, little evidence is available from prospective cohort studies. Moreover, no prospective study has addressed this association in men.


OBJECTIVE
We investigated the association between isoflavone intake and lung cancer incidence.


METHODS
We conducted a population-based prospective cohort study in 36,177 men and 40,484 women aged 45-74 y with no history of cancer at baseline in 1995-1999. Participants responded to a validated questionnaire, which included 138 food items. We used Cox proportional hazards regression analysis to estimate the hazard ratios (HRs) and 95% CIs of lung cancer incidence according to isoflavone intake, which was estimated by genistein content from soy foods.


RESULTS
During 11 y (671,864 person-years) of follow-up, we documented 481 male and 178 female lung cancer cases. In men we found an inverse association between isoflavone intake and risk of lung cancer in never smokers (n = 13,051; multivariate HR in the highest compared with the lowest quartile of isoflavone intake: 0.43; 95% CI: 0.21, 0.90; P for trend = 0.024) but not in current or past smokers. A similar, nonsignificant inverse association was seen in never-smoking women (n = 38,211; HR: 0.67; 95% CI: 0.41, 1.10; P for trend = 0.135). We also tested effect modification by smoking status (P for interaction = 0.085 in men and 0.055 in men and women combined).


CONCLUSIONS
In a large-scale, population-based, prospective study in Japan, isoflavone intake was associated with a decreased risk of lung cancer in never smokers.
Shimazu
Taichi
T
Research Center for Cancer Prevention and Screening, National Cancer Center Tokyo Japan. tshimazu@ncc.go.jp
Inoue
Manami
M
Sasazuki
Shizuka
S
Iwasaki
Motoki
M
Sawada
Norie
N
Yamaji
Taiki
T
Tsugane
Shoichiro
S
D000368:Aged; D002277:Carcinoma / Q000517:prevention & control*; D004034:Diet Surveys; D005260:Female; D005504:Food Analysis; D019833:Genistein / Q000032:analysis; D006801:Humans; D007529:Isoflavones / Q000627:therapeutic use*; D007564:Japan; D008175:Lung Neoplasms / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D048789:Phytoestrogens / Q000627:therapeutic use*; D010936:Plant Extracts / Q000627:therapeutic use*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012737:Sex Factors; D012907:Smoking; D045730:Soy Foods; D013025:Glycine max / Q000737:chemistry; D011795:Surveys and Questionnaires
D007529:Isoflavones; D048789:Phytoestrogens; D010936:Plant Extracts; D019833:Genistein