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.

Among non-smokers, the factors resulting in lung carcinogenesis are poorly understood. We conducted a hospital-based case-control analysis of 294 Chinese women, of whom 217 were non-smokers, to evaluate the role of polymorphic N-acetyltransferase (NAT2) as a susceptibility factor for the disease. The proportion of slow acetylator genotypes among non-smoking cases (n = 92) and controls (n = 125) was 38.0 and 24.0%, respectively [odds ratio (OR) 2.0, 95% confidence interval (CI) 1.1-3.7]. No effect of NAT2 genotype was seen among smokers. Among non-smokers, the effect was marked for adenocarcinomas (OR 2.1, 95% CI 1.1-4.0). As NAT2 activity is known to modify risk of arylamine-induced carcinogenesis, our results suggest that exposure to arylamines in the environment may play a role in risk of lung cancer among non-smokers.

Dietary intake of cholesterol may increase the risk of active tuberculosis, whereas marine n-3 and n-6 FAs may reduce the risk of active tuberculosis in the Chinese population.

Antioxidants may protect against oxidative stress, which is associated with tuberculosis (TB) disease. However, direct evidence for a protective association between dietary antioxidants and TB incidence in humans has been lacking. The relationship between intake of antioxidant vitamins (vitamins A, C, D, and E) and individual carotenoids (α-carotene, β-carotene, β-cryptoxanthin, lycopene, and lutein) and TB incidence was examined in the Singapore Chinese Health Study, a prospective cohort study of 63,257 adults aged 45-74 years enrolled during 1993-1998. Baseline intake of these antioxidants was estimated using a validated semiquantitative food frequency questionnaire including questions on use of dietary supplements. After an average of 16.9 years of follow-up, 1,186 incident active TB cases were identified among cohort participants. Compared with the lowest quartile, reduced risk of active TB was observed for the highest quartile of vitamin A intake (hazard ratio = 0.71, 95% confidence interval: 0.59, 0.85; P-trend < 0.01) and β-carotene intake (hazard ratio = 0.76, 95% confidence interval: 0.63, 0.91; P-trend < 0.01), regardless of smoking status. Lower TB risk was seen for vitamin C intake among current smokers only. Other vitamins and carotenoids were not associated with TB risk. These results suggest that vitamin C may reduce TB risk among current smokers by ameliorating oxidative stress, while vitamin A and β-carotene may have additional antimycobacterial properties.

No abstract