Applied nutritional investigationDietary fiber intake modifies the association between secondhand smoke exposure and coronary heart disease mortality among Chinese non-smokers in Singapore

ObjectiveSecondhand smoke (SHS) exposure increases the risk for coronary heart disease (CHD) by an estimated 25% to 30% via oxidative stress and inflammatory mechanisms that may be ameliorated by dietary components. The aim of this study was to evaluate the hypothesized modifying role of nutrients with known antioxidant and/or anti-inflammatory properties on the relationship between SHS exposure and CHD mortality.MethodsDetailed SHS exposure and dietary information was collected among 29,579 non-smokers in the Singapore Chinese Health Study, a prospective population-based cohort. The evaluation of whether or not dietary factors (β-cryptoxanthin, lutein, ω-3 polyunsaturated fatty acids, fiber, isothiocyanates, and soy isoflavones) modified the relationship between SHS exposure and CHD mortality was conducted within multivariable Cox proportional hazards models by creating an interaction term between the potential dietary effect modifier (lowest quartile of intake versus the second through fourth quartiles of intake) and the SHS exposure (none versus living with at least one smoker[s]).ResultsEvidence for a main-effects association between SHS exposure and risk for CHD mortality was not observed. In stratified analyses by levels of selected dietary nutrient intake, fiber modified the effects of SHS exposure on risk for CHD mortality (P for interaction = 0.02). The adjusted hazards ratio for SHS exposure (living with at least one smoker[s] versus living with no smokers) and CHD mortality was 1.62 (95% confidence interval, 1.00-2.63) for those with low-fiber intake. In contrast, among those with high-fiber intake, there was no association with SHS exposure.ConclusionWe provide evidence that a diet high in fiber may ameliorate the harmful effects of SHS exposure on risk for CHD mortality.