Associations of dietary supplement use with all-cause and cause-specific mortality in patients diagnosed with cancer: a large prospective cohort study in the UK Biobank

Purpose Despite the increasing popularity of supplement use among the cancer community, the current evidence on its effect on mortality in large studies is inconclusive. This study examined the association of dietary supplement use with mortality risk in a large population-based cohort. Methods This prospective cohort study analyzed data from the UK Biobank on participants who were diagnosed with cancer before July 31, 2019 and self-reported whether they had regular intake of dietary supplements (vitamins, minerals, or non-vitamin non-mineral [NVNM] supplements) after cancer diagnosis. The associations between the use of supplements with mortality were analyzed using Cox proportional hazards models, adjusting for confounders (sociodemographic factors, lifestyle and comorbidities). Results This analysis included 30,239 participants (mean age: 60.0 years; 61.9% female). Over half (57.8%) were supplement users. At a median follow-up of 11.9 years, 5577 all-cause deaths were registered. A marginal protective effect of supplement use on the risk of all-cause (adjusted hazard ratio [aHR] = 0.95, 95% CI = 0.90-0.99) and cancer (aHR = 0.89, 95% CI = 0.83-0.95) mortality were found, but not the risk of mortality due to other causes. In subgroup analyses, only NVNM dietary supplements were significantly associated with a lower risk of all-cause mortality (aHR = 0.88, 95% CI = 0.83-0.93). Both vitamins (aHR = 0.93, 95% CI = 0.87-0.99) and NVNM dietary supplements (aHR = 0.88, 95% CI = 0.82-0.94) were associated with a modest decrease in cancer mortality which were marginally significant. Conclusions This is one of the largest cohort studies that identified the associations of dietary supplements with survival in the cancer population. However, the associations are small and should be interpreted cautiously due to the variations among different supplements and the small effect size. Future studies should investigate the effect of individual supplements, particularly NVNM supplements, on improving other cancer-related outcomes.