Relationship of several serum folate forms with the risk of mortality: A prospective cohort study

We aim to examine the relation of several folate forms (5-methyltetrahydrofolate [5-mTHF], unmetabolized folic acid [UMFA], non-methyl folate, and MeFox [pyrazino-s-triazine derivative of 4α-hydroxy-5-methyltetrahydrofolate]) with the risk of mortality.

Using data from National Health and Nutrition Examination Survey 2011-2014, a total of 10,661 people with folate forms data were recruited. Death information was obtained from the National Death Index until 2015. Cox proportional hazards regression models were developed to evaluate the relationship between folate forms and mortality.

During 2.99 years of follow-up, 344 (2.6%) deaths occurred. Overall, significantly higher risks of all-cause mortality were found in participants with higher level of serum 5-mTHF (≥51.3 nmol/L [quartile 4] vs. 23.9-51.3 nmol/L [quartile 2-3]; HR, 1.61; 95% CI: 1.03-2.53), UMFA (≥1.1 nmol/L [quartile 4] vs. <1.1 nmol/L [quartile 1-3]; HR, 1.55; 95% CI: 1.15-2.09), non-methyl folate (≥1.7 nmol/L [quartile 4] vs. 1.2-1.7 nmol/L [quartile 3]; HR, 1.62; 95% CI: 1.06-2.48), or MeFox (≥2.5 nmol/L [quartile 4] vs. <2.5 nmol/L [quartile 1-3]; HR, 1.54; 95% CI: 1.11-2.12). In addition, there was an increased risk of all-cause mortality for those with low level of serum 5-mTHF (<23.9 nmol/L [quartile 1] vs. 23.9-51.3 nmol/L [quartile 2-3]; HR, 1.66; 95% CI: 1.12-2.47). Most importantly, none of any folate forms significantly modified the association between other folate forms and mortality (all P for interactions >0.05).

Higher levels of serum folate forms (5-mTHF, UMFA, non-methyl folate, and MeFox) were associated with higher risk of mortality while 5-mTHF insufficiency also showed a negative impact on mortality. Our findings emphasized the importance of monitoring the folate forms concentrations and may help counsel future related clinical trials.