Diet, reproductive factors and lung cancer risk among Chinese women in Singapore: Evidence for a protective effect of soy in nonsmokers

Abstract

The factors associated with risk of lung cancer among nonsmokers have not been fully elucidated, but dietary factors have consistently been shown to play a role. Chinese women are unique in having a high incidence of lung cancer despite a low smoking prevalence. This population is also known to have a high intake of soy, a dietary source of phytoestrogens. We conducted a hospital-based case-control study among Singapore Chinese women, comprising 303 cases and 765 age-matched controls, of whom 176 cases and 663 controls were lifetime nonsmokers. Data on demographic background, reproductive factors and dietary intake of fruit, vegetables and soy foods were obtained by in-person interview. We observed an inverse association between intake of total, cruciferous and non-cruciferous vegetables and risk of lung cancer among smokers. Although smokers in the highest tertile of fruit intake also had a lower risk, this was not statistically significant. Higher intake of soy foods significantly reduced risk of lung cancer among lifetime nonsmokers, but not among smokers. When soy isoflavonoid intake in mg/week was computed based on frequency and portion size of intake of eight common local soy foods, the adjusted OR among nonsmokers for the highest tertile compared to the lowest was 0.56, 95% CI 0.37-0.85 (p for trend <0.01). Fruit intake was also significantly associated with reduced lung cancer risk among nonsmokers, but the effect was not significant after adjustment for soy intake. On the other hand, soy intake remained an independent predictor of risk after controlling for fruit intake. Reproductive effects were also primarily confined to lifetime nonsmokers, among whom having 3 or more livebirths (adjusted OR 0.65, 0.44 -0.96) and a menstrual cycle length of more than 30 days (OR 0.46, 0.25-0.84) accorded a significantly reduced risk of lung cancer. Place of birth was significantly associated with risk among nonsmokers (OR 2.6, 1.7-3.9 for China-born vs. local born) but not among smokers. When analysis was restricted to nonsmokers with adenocarcinomas, the dietary effects were consistent or enhanced. On stepwise regression, soy intake and cycle length emerged as the independent dietary and reproductive predictors of lung cancer risk in nonsmokers. These findings are consistent with other evidence suggesting an involvement of estrogen-related pathways in lung cancer among non-smoking women.

Reproductive and hormonal factors and risk of lung cancer in women: A prospective cohort study

“…Three other studies, 21,28,29 including one from China, found no association with average length of the menstrual cycle, or with length of the menstrual period. 21 One study 29 reported a significant reduction in risk with older age at menarche, but other studies, 18,21,23,27,30 and the present study, did not find an association. A study from China 29 noted that a later age at menopause was associated with reduced risk, whereas a US study found significantly increased risk for older age at menopause.…”

“…19,22,24,25 Such differences in geographic region, as well as differences in study design and the definition of variables, make the comparison of results difficult. Two studies from East Asia 17,27 indicated that a shorter menstrual cycle is associated with increased lung cancer risk. In a third study from China, 23 squamous cell carcinoma cases had a greater total number of menstrual cycles compared to controls, and adenocarcinoma cases had shorter menstrual periods compared to controls.…”

“…[11][12][13][14][15][16] A small number of mostly case-control studies have examined the association of various reproductive and hormonal factors with lung cancer, but the results have been inconsistent. [17][18][19][20][21][22][23][24][25][26][27][28] Several studies from East Asia have shown an increased risk of lung cancer in women with shorter menstrual cycles, 17,23,27 suggesting that exposure to ovarian hormones may play a role in the disease; however, other studies have found no effect. 21,28,29 Findings regarding other reproductive variables and exogenous hormone use are also conflicting.…”

Hormone replacement therapy and lung cancer risk in Chinese

“…25 Seow et al reported a reduced lung cancer risk for those who had 3 live births or more. 30 In a recent study, Kabat et al found an inverse association between age at first live birth and lung cancer risk in parous women. 22 Brenner et al found an association between an older age at menarche and a reduced risk of lung cancer in China.…”

Lung cancer risks in relation to vegetable and fruit consumption and smoking

“…Specific dietary items in Chinese populations such as soy have been reported to be protective, 23 whereas a high consumption of milk has been reported to be a risk factor in Sweden. 16 Geographic variations in risk in central and northern Europe have been reported.…”