During an average of 9 years of follow-up, we identified 20,126 deaths in men and 11,330 deaths in women. There were 5,248 CVD deaths and 8,244 cancer deaths in men and 2,417 CVD deaths and 4,927 cancer deaths in women. Age-adjusted total, CVD, and cancer mortality rate per 100, 000 person-years was 991, 258, and 406, respectively, in men and 716, 153, and 311, respectively, in women. Energy adjusted dietary fiber intake ranged from 13 g/day (10th percentile) to 29 g/day (90th percentile) in men and from 11 g/day to 26 g/day in women. The ranges (10th–90th percentile) of energy adjusted fiber intake from grains, fruits, vegetables, and beans were 3.3–11.1, 0.9–8.0, 3.1–10.6, and 0.6–4.8 g/day, respectively, in men and 2.5–8.8, 1.0–8.1, 2.9–10.3, and 0.3–3.4 g/day, respectively, in women. Compared to individuals in the lowest quintile of dietary fiber intake, people in the highest quintile were more likely to have higher education, to self-rated their health as being very good/excellent, to have lower BMI, to be physically active, and to use menopausal hormone therapy in women, but were less likely to smoke, to drink alcohol, and to consume red meat ().
Selected characteristics of study participants by categories of dietary fiber intake
We found that dietary fiber intake was significantly inversely associated with risk of total death in both men and women (). Comparing the lowest quintile of dietary fiber intake, both men and women in the highest quintile had a 22% lower risk of total death (multivariate RRQ5 vs Q1=0.78, 95% CI: 0.73–0.82 in men; 0.78. 95% CI:0.73–0.85 in women). For an increment of 10 g/day of dietary fiber intake, the multivariate RR for total death was 0.88 (95% CI: 0.86–0.91) in men and 0.85 (95% CI: 0.82–0.89) in women. We also performed the propensity score analysis to better control for confounding and found that the results did not materially change. Comparing the highest quintile of dietary fiber intake to the lowest, RR for total death was 0.82 (95% CI:0.80–0.84) in men and 0.84 (95% CI:0.81–0.87) in women. Because smoking was a strong confounder in our analysis, we performed analyses stratified by smoking status. The association between dietary fiber intake and total death remained significantly in never smokers in both men (multivariate RRQ5 vs Q1=0.81, 95% CI: 0.71–0.93, p-trend=<0.001) and women (multivariate RRQ5 vs Q1=0.83, 95% CI:0.72–0.97, p-trend=0.05). Dietary fiber intake was also significantly inversely related to total death in former and current smokers in both men and women. A significant association with dietary fiber intake was also observed across categories of BMI. Furthermore, we examined the association stratified by age at baseline (<60 and ≥60 years old), self-rated health condition (excellent/good and fair/poor), and menopausal hormone therapy use in women (never and ever) and observed a consistently inverse association between dietary fiber intake and total death across all categories examined (data not shown).
Relative risks and 95% confidence intervals of total death for quintiles of dietary fiber intake in men and women
Correction for measurement error in the assessments of dietary fiber intake strengthened the association with total mortality. For an increment of 10 g/day of dietary fiber intake, the RRs of total death, adjusting for age, smoking, and total energy intake, was 0.86 (95% CI: 0.84–0.88) in men and 0.83 (95% CI:0.80–0.86) in women before measurement error correction. After correcting for measurement error, the RR were 0.76 (95% CI:0.72–0.80) in men and 0.71 (95% CI:0.66–0.76) in women.
Dietary fiber intake was also inversely related to risk of death from CVD, cancer, and infectious and respiratory diseases in men (). Comparing the highest to the lowest quintile of dietary fiber intake, men had a 24% – 56% lower risk of death from CVD, cancer, and infectious and respiratory diseases. Comparable findings in women were a 34%–59% lower risk of death from CVD and infectious and respiratory diseases and no association with cancer death (). For every 10 g/day increase in dietary fiber intake, the multivariate RRs for death from CVD, cancer, and infectious and respiratory diseases were 0.88 (95% CI: 0.86–0.91), 0.92 (95% CI: 0.88–0.96), 0.66 (95% CI: 0.52–0.84) and 0.82 (95% CI: 0.74–0.93), respectively, in men and 0.76 (95% CI: 0.69–0.84), 0.97 (95% CI: 0.91–1.04), 0.61 (95% CI: 0.44–0.85) and 0.66 (95% CI: 0.56–0.78), respectively, in women.
Relative risks and 95% confidence intervals of cause-specific death for quintiles of dietary fiber intake in men
Relative risks and 95% confidence intervals of cause-specific death for quintiles of dietary fiber intake in women
We further adjusted for aspirin use, high blood pressure, and cholesterolemia and found no appreciable differences. In addition, we analyzed the data by excluding death occurring the first 2 to 4 years of follow-up and found no change in results. When we restricted analyses to never smokers, the multivariate RRQ5 vs Q1 of death from CVD, cancer, and infectious and respiratory diseases in men were 0.95 (95% CI: 0.74–1.21, p-trend=0.81, 1134 death), 0.82 (95% CI: 0.65–1.03, p-trend= 0.009, 1405 death), 0.22 (95% CI: 0.08–0.61, p-trend= 0.002, 70 death), and 0.60 (95% CI: 0.25–1.44, p-trend=0.20, 90 death), respectively. In never smoked women, the multivariate RRQ5 vs Q1 were 0.69 (95% CI: 0.50–0.95, p-trend= 0.02, 729 death) for CVD death, 1.14 (95% CI: 0.90–1.44, p-trend=0.11, 1342 death) for cancer death, 0.28 (95% CI: 0.10–0.80, p-trend=0.02, 70 death) for infectious disease death, and 0.50 (95% CI: 0.22–1.14, p-trend=0.07, 103 death) for respiratory disease death.
Fiber intakes from food sources such as grains, fruits, vegetables and beans were also examined (). We found that dietary fiber from grains was significantly inversely related to risk of total, CVD, cancer, and respiratory disease death in both men and women. Comparing the highest to the lowest intake of fiber from grains, men had a 22% lower risk of total death (multivariate RR=0.77, 95% CI:0.73–0.81) and women had a 19% lower risk of total death (multivariate RR=0.81, 95% CI:0.76–0.86). Fiber from vegetables and beans was also weakly associated with lower risk of total death in both men and women. However, fiber from fruits was not related to total and cause-specific death in men and women.
Multivariate relative risk of total and cause-specific death comparing the highest vs. the lowest quintile of fiber intake from food sources