Association of Dietary Fiber and Yogurt Consumption With Lung Cancer Risk: A Pooled Analysis

Abstract

Importance: Dietary fiber (the main source of prebiotics) and yogurt (a probiotic food) confer various health benefits via modulating the gut microbiota and metabolic pathways. However, their associations with lung cancer risk have not been well investigated.

Objective: To evaluate the individual and joint associations of dietary fiber and yogurt consumption with lung cancer risk and to assess the potential effect modification of the associations by lifestyle and other dietary factors.

Design, setting, and participants: This pooled analysis included 10 prospective cohorts involving 1 445 850 adults from studies that were conducted in the United States, Europe, and Asia. Data analyses were performed between November 2017 and February 2019. Using harmonized individual participant data, hazard ratios and 95% confidence intervals for lung cancer risk associated with dietary fiber and yogurt intakes were estimated for each cohort by Cox regression and pooled using random-effects meta-analysis. Participants who had a history of cancer at enrollment or developed any cancer, died, or were lost to follow-up within 2 years after enrollment were excluded.

Exposures: Dietary fiber intake and yogurt consumption measured by validated instruments.

Main outcomes and measures: Incident lung cancer, subclassified by histologic type (eg, adenocarcinoma, squamous cell carcinoma, and small cell carcinoma).

Results: The analytic sample included 627 988 men, with a mean (SD) age of 57.9 (9.0) years, and 817 862 women, with a mean (SD) age of 54.8 (9.7) years. During a median follow-up of 8.6 years, 18 822 incident lung cancer cases were documented. Both fiber and yogurt intakes were inversely associated with lung cancer risk after adjustment for status and pack-years of smoking and other lung cancer risk factors: hazard ratio, 0.83 (95% CI, 0.76-0.91) for the highest vs lowest quintile of fiber intake; and hazard ratio, 0.81 (95% CI, 0.76-0.87) for high vs no yogurt consumption. The fiber or yogurt associations with lung cancer were significant in never smokers and were consistently observed across sex, race/ethnicity, and tumor histologic type. When considered jointly, high yogurt consumption with the highest quintile of fiber intake showed more than 30% reduced risk of lung cancer than nonyogurt consumption with the lowest quintile of fiber intake (hazard ratio, 0.67 [95% CI, 0.61-0.73] in total study populations; hazard ratio, 0.69 [95% CI, 0.54-0.89] in never smokers), suggesting potential synergism.

Conclusions and relevance: Dietary fiber and yogurt consumption was associated with reduced risk of lung cancer after adjusting for known risk factors and among never smokers. Our findings suggest a potential protective role of prebiotics and probiotics against lung carcinogenesis.

Figure 1.. Flow Diagram of Study Participant Selection and Exclusion

AARP indicates National Health Institute-AARP Diet and Health Study; EPIC, European Prospective Investigation into Cancer and Nutrition; HPFS, Health Professionals Follow-up Study; IWHS, Iowa Women’s Health Study; NHS, Nurses’ Health Study; PLCO, Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial; SCCS, Southern Community Cohort Study; SMHS, Shanghai Men’s Health Study; SWHS, Shanghai Women’s Health Study, and VITAL, Vitamins and Lifestyle Study.

Figure 2.. Risk of Lung Cancer by Dietary Fiber Intake and Yogurt Consumption in Subgroups of Participants

Hazard ratios (HRs) and 95% CIs were estimated by random-effects meta-analyses based on the sex-specific quintiles of total dietary fiber intake or yogurt consumption (none, 0 g/d; low, ≤sex-specific median intake; high, >sex-specific median intake). Participants from the Shanghai Men’s and Women’s Health Studies were included in the fiber-lung cancer analysis only. No data were available on yogurt consumption in these 2 cohorts. Age, saturated fat intake, and follow-up time were grouped by their median values. Heavy drinkers were defined as alcohol consumers who reported ethanol consumption of more than 28 g per day in men or more than 14 g per day in women; and moderate drinkers were defined as alcohol consumers who reported ethanol consumption of greater than 0 to 28 g per day in men or greater than 0 to 14 g per day in women. Physical activity levels were defined as tertiles of total physical active hours or metabolic equivalent hours. All models were stratified by birth year and enrollment year and adjusted for age, total energy, smoking status, smoking pack-years, sex, race/ethnicity, educational level, obesity status, diabetes, family history of lung cancer, physical activity level, menopausal status in women, and intakes of saturated and polyunsaturated fat.