Association of serum folate concentrations with the mortality of cancer: a prospective cohort study

The association between serum folate concentrations and the mortality of cancer remains unclear. We aim to investigate the association of serum folate concentrations with all-cause and cause-specific mortality among American adults with cancer.

This cohort study included 4535 patients with cancer from National Health and Nutrition Examination Survey (NHANES) 1999 to 2016 and NHANES III (1988–1994). Death outcomes were ascertained by linkage to National Death Index records through 31 December 2019. Cox proportional hazards model and two-piecewise Cox proportional hazards model were used to calculate hazard ratios and 95% confidence intervals for the associations between folate concentrations and the risk of mortality.

During a median follow-up of 37,792 person-years, there were 1998 all-cause deaths and 616 cancer deaths. Non-linear and L-shaped associations were observed between serum folate concentrations and the risk of all-cause and cancer mortality among patients with cancer. Notably, the mortality rates reached a plateau at 23.7 ng/mL for all-cause mortality and 23.57 ng/mL for cancer mortality. When folate levels fell below these thresholds, the risk of all-cause and cancer mortality decreased by approximately 2.1% (HR 0.979; 95% CI 0.969–0.989) and 3.6% (HR 0.964; 95% CI 0.948–0.981), respectively, with each unit increase in the folate concentration up to the thresholds.

Our study reveals that low serum folate concentrations are linked to an elevated risk of cancer mortality among individuals with cancer within a certain range and supplementation of folate in cancer patients to achieve specific serum folate level threshold (23.7 ng/mL) might reduce the risk of cancer mortality.