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

Folate Biomarkers, Folate Intake, and Risk of Death From All Causes, Cardiovascular Disease, and Cancer: A Systematic Review and Dose-Response Meta-Analysis of Prospective Cohort Studies

CONTEXT

Existing evidence on the relation between folate intake and biomarkers with mortality risk is controversial.

OBJECTIVE

Previous cohort studies were examined regarding folate intake and biomarkers in relation to risk of all-cause, cardiovascular disease- (CVD), and cancer-related mortality through a systematic review and meta-analysis.

DATA SOURCES

A systematic search was performed of the PubMed, Scopus, and ISI Web of Science databases up to July 2023.

DATA EXTRACTION

Prospective cohort studies examining the association of folate biomarkers (in serum, plasma, red blood cells) and intake with risk of all-cause, CVD-, and cancer-related mortality were considered. A random-effects model was applied to combine study-specific risk estimates. Dose-response relations were assessed by 1-stage weighted mixed-effects meta-analysis.

DATA ANALYSIS

A total of 25 cohorts with 423 304 participants, 36 558 all-cause, 12 662 CVD-, and 2426 cancer-related deaths were included. No significant association was observed between the highest levels of folate biomarkers and all-cause mortality risk (hazard ratio [HR], 0.91; 95% CI, 0.77-1.06; n = 17; I2 = 89.4%; P < .001), CVD-related mortality risk (HR, 0.97; 95% CI, 0.87-1.06; n = 11; I2 = 0.0%; P = .57), and cancer-related mortality risk (HR, 0.85; 95% CI, 0.69-1.05; n = 6; I2 = 57.8%; P = .04) compared with the lowest. Furthermore, each 10 nmol/L increase was marginally related to a 12% reduced all-cause mortality risk but not to CVD- and cancer-related mortality risk. A significant inverse association was found between highest intake of dietary folate and the lowest, and risk of all-cause (HR, 0.87; 95% CI, 0.78-0.96; n = 3; I2 = 63.6%; P = .06) and CVD (HR, 0.77; 95% CI, 0.57-0.93; n = 4; I2 = 80.2%; P = .002) mortality.

CONCLUSIONS

This meta-analysis revealed a significant inverse relation between dietary folate intake and risk of all-cause and CVD mortality. Such an association was not found in the case of folate biomarkers. Further prospective studies are warranted to confirm these findings.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42023401700.

Relationship of dietary intake of food folate and synthetic folic acid intake from fortified foods with all-cause mortality in individuals with chronic kidney disease

OBJECTIVE

To evaluate the association of the dietary intake of food folate (natural folate) and synthetic folic acid intake from fortified foods with the risk of all-cause mortality and end-stage kidney disease (ESKD) among the chronic kidney disease (CKD) population in regions with folic acid fortification.

METHODS

4028 individuals with established CKD in Chronic Renal Insufficiency Cohort (CRIC) were included. Diet was assessed using a validated diet history questionnaire at the baseline, year 2, and year 4, and nutrient intake, including food folate and folic acid from fortified foods, was estimated using the National Nutrient Database. The outcomes were all-cause mortality and ESKD. The results for all-cause mortality were further validated using the data from National Health and Nutrition Examination Surveys (NHANES).

RESULTS

During a median follow-up of 11.1 years, 1155 deaths and 938 ESKD cases occurred. Compared with the first quartile of food folate intake, the third (HR: 0.74; 95% CI: 0.62, 0.90) and fourth (HR: 0.79; 95% CI: 0.63, 0.98) quartiles had a lower risk of all-cause mortality. Nevertheless, there was no significant association of synthetic folic acid intake from fortified foods with all-cause mortality. Similar results were observed for ESKD. Consistently, in NHANES, food folate intake and serum 5-methyltetrahydrofolate, but not folic acid intake, were inversely associated with all-cause mortality, while serum unmetabolized folic acid was positively associated with all-cause mortality in CKD participants.

CONCLUSIONS

Higher intake of dietary natural folate, but not synthetic folic acid intake from fortified foods, was associated with lower risks of all-cause mortality and ESKD among CKD participants.

Uncovering the Hidden Dangers and Molecular Mechanisms of Excess Folate: A Narrative Review

This review delves into the intricate relationship between excess folate (vitamin B9) intake, especially its synthetic form, namely, folic acid, and its implications on health and disease. While folate plays a pivotal role in the one-carbon cycle, which is essential for DNA synthesis, repair, and methylation, concerns arise about its excessive intake. The literature underscores potential deleterious effects, such as an increased risk of carcinogenesis; disruption in DNA methylation; and impacts on embryogenesis, pregnancy outcomes, neurodevelopment, and disease risk. Notably, these consequences stretch beyond the immediate effects, potentially influencing future generations through epigenetic reprogramming. The molecular mechanisms underlying these effects were examined, including altered one-carbon metabolism, the accumulation of unmetabolized folic acid, vitamin-B12-dependent mechanisms, altered methylation patterns, and interactions with critical receptors and signaling pathways. Furthermore, differences in the effects and mechanisms mediated by folic acid compared with natural folate are highlighted. Given the widespread folic acid supplementation, it is imperative to further research its optimal intake levels and the molecular pathways impacted by its excessive intake, ensuring the health and well-being of the global population.

Combined use of amlodipine and folic acid are significantly more efficacious than amlodipine alone in lowering plasma homocysteine and blood pressure among hypertensive patients with hyperhomocysteinemia and intolerance to ACEI: A multicenter, randomized, double-blind, parallel-controlled clinical trial

Hyperhomocysteinemia with hypertension can synergistically increase the risk of stroke. The China stroke primary prevention trial showed that combining 0.8 mg folic acid (FA) with angiotensin-converting enzyme inhibitor (ACEI) can effectively lower plasma total homocysteine (tHcy) and blood pressure (BP); and reduce first stroke risk by additional 21% compared to ACEI alone. However, intolerance to ACEI is common in Asians and amlodipine can be alternative. This is a multicenter, randomized, double-blind, parallel-controlled clinical trial (RCT) which evaluated whether amlodipine combined with FA is more efficacious than amlodipine alone in lowering tHcy and BP among Chinese hypertensive with hyperhomocysteinemia and intolerance to ACEI. 351 Eligible patients were randomly assigned by 1:1:1 ratio to receive amlodipine-FA tablet daily (amlodipine 5 mg/FA 0.4 mg, A group); amlodipine 5 mg/FA 0.8 mg tablet daily (B group); amlodipine 5 mg daily (C group, control group). Follow-up was conducted at 2, 4, 6, and 8 weeks. The primary outcome was efficacy of lowering both tHcy and BP at the end of 8-week treatment. Compared with C group, A group had a significantly higher rate of lowering both tHcy and BP (23.3% vs. 6.0%; Odds Ratio [OR], 8.68; 95% CI, 3.04-24.78, P < .001); B group also had a higher rate of lowering both tHcy and BP (20.3% vs. 6.0%; OR: 5.90; 95% CI, 2.11-16.47, P < .001). This RCT showed amlodipine combined with FA compared with amlodipine alone, each had significantly higher efficacy of lowering both tHcy and BP. No difference was found in BP-lowering and occurrence of adverse events between the three groups.

Folate, folic acid, and chemotherapy-induced toxicities: a systematic literature review

Folate metabolism is a target for various chemotherapeutic drugs. Folate and its synthetic variant folic acid are B-vitamins. To what extent these vitamins impact treatment tolerance in patients with cancer remains unclear. A systematic literature review was conducted on intake and status of folate and folic acid in relation to chemotherapy-induced toxicities in children and adults with cancer. A total of 6,231 publications were identified, of which 40 publications met the inclusion criteria. In 12 out of 22 studies focusing on antifolates, a deficient folate status and lower folate and folic acid intake were associated with a higher risk of toxicities. In 8 out of 14 studies focusing on fluoropyrimidine treatments, a higher folate status and intake were associated with a higher risk of toxicities. These findings might explain interindividual differences in treatment tolerance and highlight the importance of evaluating nutritional status in oncology care.

Non-linear associations of serum and red blood cell folate with risk of cardiovascular and all-cause mortality in hypertensive adults

This study aims to assess the associations of serum and red blood cell (RBC) folate with cardiovascular and all-cause mortality in hypertensive adults. Data on serum and RBC folate from the 1999-2014 National Health and Nutrition Examination Survey were included. Through December 31, 2015, cardiovascular and all-cause mortality were identified from the National Death Index. Multiple Cox regression and restricted cubic spline analyses were used to determine the relationship between folate concentrations and outcomes. A total of 13,986 hypertensive adults were included in the analysis (mean age, 58.5 ± 16.1 years; 6898 [49.3%] men). At a median of 7.0 years of follow-up, 548 cardiovascular deaths and 2726 all-cause deaths were identified. After multivariable adjustment, the fourth quartile of serum folate was associated with cardiovascular (HR = 1.32 [1.02-1.70]) and all-cause (HR = 1.20 [1.07-1.35]) mortality compared to the second quartile, whereas the first quartile was only linked with increased all-cause (HR = 1.29 [1.15-1.46]) mortality. The inflection points for the non-linear associations of serum folate with cardiovascular and all-cause mortality were 12.3 ng/mL and 20.5 ng/mL, respectively. In addition, the highest quartile of RBC folate was associated with cardiovascular (HR = 1.68 [1.30-2.16]) and all-cause (HR = 1.30 [1.16-1.46]) mortality compared to the second quartile, but the lowest quartile was not associated with either outcome. The inflection points for the non-linear associations of RBC folate with cardiovascular and all-cause mortality were 819.7 and 760.1 ng/mL, respectively. The findings suggest non-linear associations between serum and RBC folate levels and the risk of cardiovascular and all-cause mortality in hypertensive adults.

Associations between Serum Folate Concentrations and Functional Disability in Older Adults

Folate may have beneficial effects on physical function through its antioxidant effect. Thus, we investigated the associations between serum folate and functional disability in older adults. Data from the National Health and Nutrition Examination Survey 2011–2018 were used. Serum folate included 5-methyltetrahydrofolate and total folate. Five domains of functional disability, including lower extremity mobility (LEM), instrumental activities of daily living (IADL), activities of daily living (ADL), leisure and social activities (LSA), and general physical activities (GPA), were self-reported. Multivariable-adjusted logistic regression models and restricted cubic splines were employed. 5-Methyltetrahydrofolate was inversely associated with IADL and GPA disability, and the multivariate-adjusted ORs (95% CIs) in the highest versus lowest quartiles were 0.65 (0.46–0.91) and 0.70 (0.50–0.96), respectively. The total folate was also inversely associated with IADL (OR quartile 4vs1 = 0.65, 95% CI: 0.46–0.90) and GPA (OR quartile 3vs1 = 0.66, 95% CI: 0.44–0.99) disability. The dose–response relationships showed a gradual decrease in the risk of IADL and GPA disability as serum folate increased. In the sex, age, BMI, and alcohol consumption subgroup analyses, we saw that the associations were primarily found in females, under 80 years old, normal weight, and non-drinkers. Sensitivity analyses further confirmed the robustness of our results. Our results indicated that serum folate concentrations were negatively associated with IADL and GPA disability, especially in females. In other subgroup analyses, we discovered that these negative associations were primarily prevalent in participants under 80 years old, normal weight, and non-drinkers.

Effect of folic acid supplementation on the change of plasma S-adenosylhomocysteine level in Chinese hypertensive patients: a randomized, double-blind, controlled clinical trial

The relationship between folic acid and S-adenosylhomocysteine (SAH) is controversial. This study aims to explore the effect of different doses of folic acid supplementation on SAH levels in hypertensive patients and the modification of methylene-tetrahydrofolate reductase (MTHFR) C677T gene polymorphism. A randomized, double-blind, controlled clinical trial was conducted. Hypertensive patients aged 45-75 years without a history of stroke and cardiovascular disease were selected, who were randomly assigned to one of 8 dose groups. This trial has been registered with Trial Number: ChiCTR1800016135. In the total population, folic acid supplementation of 0.4-2.0 mg/day had no effect on SAH level (β = 0.47, 95% CI: -0.86-1.79, p = 0.491), while folic acid supplementation of 2.4 mg/day significantly increased SAH level (β = 1.93, 95% CI: 0.22-3.64, p = 0.027). Stratified analysis found that MTHFR C677T genotype CC supplemented with 2.4 mg/day folic acid had no effect on SAH level (β = 0.30, 95% CI: -2.74-3.34, p = 0.847), while CT and TT genotype supplemented with 2.4 mg/day folic acid showed a significant increase in SAH level (CT: β = 2.98, 95% CI: 0.34-5.62, p = 0.027; TT: β = 3.00, 95% CI: -0.51-6.51, p = 0.095; CT combined with TT: β = 2.99, 95% CI: 0.90-5.09, p = 0.005). In conclusion, supplementation of 2.4 mg/day folic acid can lead to increased SAH levels, especially in MTHFR C677T genotype CT and TT.

Associations of Serum and Red Blood Cell Folate With All-Cause and Cardiovascular Mortality Among Hypertensive Patients With Elevated Homocysteine

Objectives

This study aims to explore the associations between serum and red blood cell (RBC) folate as indicators of short- and long-term folate status, respectively, and all-cause as well as CVD mortality among hypertensive patients with elevated homocysteine.

Methods

A prospective cohort study of the National Health and Nutrition Examination Survey (1999–2006) and 2015 Linked Mortality File was performed. All-cause and CVD mortality risk estimated using Cox proportional hazards models with adjusting for multiple potential covariates.

Results

A total of 1,753 hypertensive patients with elevated homocysteine [mean (SD) age, 68.5 (13.1)] were included in the analysis. During a median follow-up of 10.0 years, a total of 899 all-cause and 257 CVD deaths occurred. Compared the highest with the lowest quartile of RBC folate, the multivariable adjusted hazard ratios and 95% confidence intervals for all-cause and CVD death were 1.13 (0.92–1.39) and 1.47 (1.01–2.16) respectively. There was a significant and positive trend between RBC folate and the risk of CVD death (p for trend = 0.0196). No significant association was found between serum folate and mortality risk among the study sample.

Conclusions

High level of RBC folate is associated with an increased risk of cardiovascular mortality among hypertensive patients with elevated homocysteine while serum folate has no such effects.

Relationship of several serum folate forms with kidney function and albuminuria: cross-sectional data from the National Health and Nutrition Examination Surveys (NHANES) 2011-2018

We aim to examine the relation of several folate forms (5-methyltetrahydrofolate (5-mTHF), unmetabolised folic acid (UMFA) and MeFox) with kidney function and albuminuria, which remained uncertain. The cross-sectional study was conducted in 18 757 participants from National Health and Nutrition Examination Survey 2011-2018. The kidney outcomes were reduced estimated glomerular filtration rate (eGFR) (<60 ml/min/1·73 m2), microalbuminuria (albumin:creatinine ratio (ACR) of 30-299 mg/g) and macroalbuminuria (ACR ≥ 300 mg/g). Overall, there were significant inverse associations between serum 5-mTHF and kidney outcomes with significant lower prevalence of reduced eGFR (OR, 0·71; 95 % CI: 0·57, 0·87) and macroalbuminuria (OR, 0·65; 95 % CI: 0·46, 0·91) in participants in quartiles 3-4 (v. quartiles 1-2; both Pfor trend across quartiles <0·05). In contrast, there were significant positive relationship between serum UMFA and kidney outcomes with significant higher prevalence of reduced eGFR in participants in quartiles 2-4 (v. quartile 1; OR, 2·12; 95 % CI: 1·45, 3·12; Pfor trend <0·001) and higher prevalence of macroalbuminuria in participants in quartile 4 (v. quartiles 1-3; OR, 1·46; 95 % CI: 1·06, 2·01; Pfor trend <0·001). However, there was no significant associations of 5-mTHF and UMFA with microalbuminuria. In addition, there were significant positive relationships of serum MeFox with reduced eGFR, microalbuminuria and macroalbuminuria (all Pfor trend <0·01). In conclusion, higher 5-mTHF level, along with lower UMFA and MeFox level, was associated with lower prevalence of kidney outcomes, which may help counsel future clinical trials and nutritional guidelines regarding the folate supplement.