Key words: colorectal cancer, cancer survivors, dietary supplements, vitamin status, fatigue, quality of life

"The value of vitamins after a colorectal cancer diagnosis: Associations of vitamin D, B-vitamins, and supplement use with fatigue and quality of life"

A growing number of patients survive colorectal cancer. Patients often continue to experience health problems that negatively impact their quality of life in the years after treatment. This research aimed to obtain insight in the role of supplements, vitamin D, and B-vitamins (status and intake) in relation to quality of life and fatigue in colorectal cancer survivors. Associations were observed between the use of supplements and increased fatigue, which implies that colorectal cancer survivors may initiate the use of supplements as a consequence of fatigue. Furthermore, biomarker concentrations of vitamin D and vitamin B6 were associated with better quality of life outcomes. Vitamin D and B6 are therefore promising leads for future studies in this field. Important implications that were drawn from this thesis are the need for attention and alertness among health care professionals about the use of supplements by colorectal cancer survivors, the need for increased recognition and dialogue about the symptom of fatigue, and more awareness on the prevalence and consequences of vitamin deficiencies in this population.