Sources of dietary fiber and risk of colorectal cancer: results from the HELGA cohort
Louise Hansen et. al., Institute of Cancer Epidemiology, Danish Cancer Society, Copenhagen, Denmark
Intake of dietary fiber has for many years been hypothesized to reduce colorectal cancer (CRC) risk. Potential mechanisms for this effect include dilution of fecal carcinogens, reduction of bowel transit time, production of short chain fatty acids or binding of carcinogenic bile acids. While intervention studies using fiber supplements have largely failed to find an association, results from prospective, observational studies indicate a possible protective role for dietary fiber consumption in relation to CRC.
The present study examined associations between intake of dietary fiber from various sources in the diet and risk of colon and rectal cancer in a prospective cohort study.
Materials and methods
The HELGA cohort consists of the Diet, Cancer and Health cohort (Denmark), Västerbotten Intervention Project (Sweden) and Norwegian Women and Cancer Study (Norway). The study investigated dietary fiber intake overall but also intake from various sources (including cereals, fruits/vegetables). This topic has been investigated previously in an EPIC study, but the current project included more cancer cases from updated registries and had a specific Nordic focus.
The HELGA cohort was followed for cancer incidence using information from cancer registries, patient registries and cause of death registries until ultimo 2006. Baseline intake of dietary fiber from various sources was estimated based on a validated food frequency questionnaire, and associations between exposures and cancer incidence rate ratios were based on Cox proportional hazards models. Models presented are multivariable, adjusted for common CRC risk factors.
Preliminary results
In total 116,399 persons, including 739 CRC cases, were included in the analyses. Cases had a higher BMI, lower education, higher meat and alcohol intake, and more were smokers. A lower colon cancer incidence was seen for higher intake of total fiber (IRR per 5 g/d: 0.93, 95% CI: 0.87-0.99). Higher intake of cereal fiber per 2.5 g/d was associated with lower CRC incidence (IRR (95% CI): 0.96 (0.92-0.99) and CC: (0.94 (0.89-0.98). The strongest association for subtype of CC was seen for proximal CC. No associations were seen for rectal cancer alone. In conclusion, we found that higher intake of dietary fiber overall and fiber from cereals, but not fiber from fruits or vegetables, was associated with lower incidence of CRC.
Data analysis is still on-going; thus, these data are preliminary. It is the aim to further investigate dietary fiber intake by grouping the fibers in a more biochemically correct way than previously and relate this to CRC.