Dietary supplement use has exploded over the past decades. The World Cancer Research Fund and the American Institute for Cancer Research advises against the use of supplements for cancer prevention, and recommends to meet nutritional needs through diet alone. Up to now, it is not yet clear whether this recommendation for habitual dietary supplement use also applies to the general population.
The overall aim of this thesis is to improve our knowledge about the role of dietary supplement use in colorectal tumor development in the general population and in populations at high risk for colorectal tumors, and to gain insight into the consistency of dietary supplement use over time in patients diagnosed with colorectal cancer.
The results in this thesis do not point toward a preventive nor a harmful role for dietary supplement use in colorectal tumor risk and recurrence in the general population and in high-risk populations for colorectal cancer. Therefore, dietary supplements are not recommended for primary or tertiary prevention of colorectal cancer. Furthermore, dietary supplement use appeared to be inconsistent over time after colorectal cancer diagnosis, during and after cancer therapy. Future observational research on the role of dietary supplement use for primary or tertiary prevention of colorectal tumors should continue.