Original Article| Volume 43, ISSUE 12, e346-e363, December 2021

The Effects of Folic Acid Supplementation on Pro-inflammatory Mediators: a Systematic Review and Dose–Response Meta‐Analysis of Randomized Controlled Trials


      • Folic acid supplementation reduced serum levels of CRP in adults, particularly in trials that prescribed folic acid at doses less than 5mg/d for more than 12 weeks.
      • Folic acid supplementation decreased serum TNF-α concentrations in adults, especially in trials that prescribed folic acid at doses <5mg/d and >12 weeks.
      • Folic acid supplementation decreased serum IL-6 levels in adults, notably in studies administered folic acid at doses < 1mg/d and including more than 50 participants.



      Despite extensive research, findings regarding the effects of folic acid supplementation on inflammatory mediators have been controversial and inconclusive. This study therefore aimed to summarize the findings of all available clinical trials regarding the effects of folic acid supplementation on inflammatory biomarkers in adults.


      A systematic search was conducted of PubMed/MEDLINE, Scopus, Web of Science, EMBASE, and Google Scholar until April 2020. All randomized controlled trials that examined the influence of folic acid supplementation on C-reactive protein, interleukin 6 (IL-6), and tumor necrosis factor-α (TNF-α) were included. Pooled effect sizes were calculated based on the random effects model, and dose–response analysis was modeled by using a fractional polynomial model.


      In total, 18 randomized controlled trials involving 2286 participants were analyzed. Folic acid supplementation significantly reduced serum levels of C-reactive protein (mean difference [MD], –0.21 mg/L; 95% CI, –0.41 to –0.01; n = 16), TNF-α (MD, –14.88 pg/mL; 95% CI, –23.68 to –6.09; n = 10), and IL-6 (MD, –0.93 pg/mL; 95% CI, –1.72 to –0.14; n = 11). Subgroup analyses suggested a significant reduction at doses ≤5 mg/d and studies longer than 12 weeks in duration. A significant nonlinear association was also found between folic acid dosage (Pnonlinearity <0.001) and duration of administration (Pnonlinearity <0.001) with serum TNF-α levels.


      This meta-analysis indicates the beneficial effects of folic acid supplementation on pro-inflammatory cytokines. Further studies with a longer duration of administration, higher doses, and larger sample sizes should be performed exclusively on patients with chronic inflammatory disorders to elucidate the favorable role of folate intake on inflammatory biomarkers. International Prospective Register of Systematic Reviews identifier: CRD42021249947.

      Key words

      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'


      Subscribe to Clinical Therapeutics
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Robertson CM
        • Coopersmith CM.
        The systemic inflammatory response syndrome.
        Microbes Infect. 2006; 8: 1382-1389
        • Carlberg C
        • Ulven SM
        • Molnár F.
        Chronic inflammation and metabolic stress.
        Nutrigenomics. 2016; : 121-137
        • Wellen KE
        • Hotamisligil GS.
        Inflammation, stress, and diabetes.
        J Clin Invest. 2005; 115: 1111-1119
        • An R
        • Ji M
        • Zhang S.
        Global warming and obesity: a systematic review.
        Obes Rev. 2018; 19: 150-163
        • Guarner V
        • Rubio-Ruiz ME.
        Low-grade systemic inflammation connects aging, metabolic syndrome and cardiovascular disease.
        Interdiscip Top Gerontol. 2015; 40: 99-106
        • Pietrzyk L
        • Torres A
        • Maciejewski R
        • Torres K.
        Obesity and obese-related chronic low-grade inflammation in promotion of colorectal cancer development.
        Asian Pac J Cancer Prev. 2015; 16: 4161-4168
        • Van Greevenbroek M
        • Schalkwijk C
        • Stehouwer C.
        Obesity-associated low-grade inflammation in type 2 diabetes mellitus: causes and consequences.
        Neth J Med. 2013; 71: 174-187
        • Nowbar AN
        • Gitto M
        • Howard JP
        • Francis DP
        • Al-Lamee R.
        Mortality from ischemic heart disease: analysis of data from the World Health Organization and coronary artery disease risk factors from NCD Risk Factor Collaboration.
        Circ Cardiovasc Qual Outcomes. 2019; 12e005375
        • Bennett JE
        • Stevens GA
        • Mathers CD
        • et al.
        NCD Countdown 2030: worldwide trends in non-communicable disease mortality and progress towards Sustainable Development Goal target 3.4.
        The Lancet. 2018; 392: 1072-1088
        • Pahwa R
        • Goyal A
        • Bansal P
        • Jialal I.
        Chronic inflammation.
        StatPearls [Internet]. 2020;
        • Toraldo D
        • Nuccio FD
        • Scoditti E.
        Systemic inflammation in chronic obstructive pulmonary disease: may diet play a therapeutic role.
        J Aller Ther S. 2013; 2: 2
        • Rahimnia A-R
        • Panahi Y
        • Alishiri G
        • Sharafi M
        • Sahebkar A.
        Impact of supplementation with curcuminoids on systemic inflammation in patients with knee osteoarthritis: findings from a randomized double-blind placebo-controlled trial.
        Drug Res. 2015; 65: 521-525
        • Mousavi SM
        • Djafarian K
        • Mojtahed A
        • Varkaneh HK
        • Shab-Bidar S.
        The effect of zinc supplementation on plasma C-reactive protein concentrations: a systematic review and meta-analysis of randomized controlled trials.
        Eur J Pharmacol. 2018; 834: 10-16
        • Friso S
        • Jacques PF
        • Wilson PW
        • Rosenberg IH
        • Selhub J.
        Low circulating vitamin B6 is associated with elevation of the inflammation marker C-reactive protein independently of plasma homocysteine levels.
        Circulation. 2001; 103: 2788-2791
        • Morris MS
        • Sakakeeny L
        • Jacques PF
        • Picciano MF
        • Selhub J.
        Vitamin B-6 intake is inversely related to, and the requirement is affected by, inflammation status.
        J Nutr. 2010; 140: 103-110
        • Scaglione F
        • Panzavolta G.
        Folate, folic acid and 5-methyltetrahydrofolate are not the same thing.
        Xenobiotica. 2014; 44: 480-488
        • Lind MV
        • Lauritzen L
        • Kristensen M
        • Ross AB
        • Eriksen JN.
        Effect of folate supplementation on insulin sensitivity and type 2 diabetes: a meta-analysis of randomized controlled trials.
        Am J Clin Nutr. 2019; 109: 29-42
        • Sarna LK
        • Wu N
        • Wang P
        • Hwang S-Y
        • Siow YL
        • O K
        Folic acid supplementation attenuates high fat diet induced hepatic oxidative stress via regulation of NADPH oxidase.
        Can J Physiol Pharmacol. 2012; 90: 155-165
        • McRae MP.
        High-dose folic acid supplementation effects on endothelial function and blood pressure in hypertensive patients: a meta-analysis of randomized controlled clinical trials.
        J Chiropr Med. 2009; 8: 15-24
        • Solini A
        • Santini E
        • Ferrannini E.
        Effect of short-term folic acid supplementation on insulin sensitivity and inflammatory markers in overweight subjects.
        Int J Obes. 2006; 30: 1197-1202
        • Li M
        • Li W
        • Gao Y
        • et al.
        Effect of folic acid combined with docosahexaenoic acid intervention on mild cognitive impairment in elderly: a randomized double-blind, placebo-controlled trial.
        Eur J Nutr. 2020; : 1-14
        • Bahmani F
        • Karamali M
        • Shakeri H
        • Asemi Z.
        The effects of folate supplementation on inflammatory factors and biomarkers of oxidative stress in overweight and obese women with polycystic ovary syndrome: a randomized, double-blind, placebo-controlled clinical trial.
        Clin Endocrinol (Oxf). 2014; 81: 582-587
        • Bahmani F
        • Galougahi FR
        • Vahedpoor Z
        • et al.
        The effects of folic acid supplementation on recurrence and metabolic status in endometrial hyperplasia: a randomized, double-blind, placebo-controlled trial.
        Arch Iran Med. 2018; 21: 452-459
        • Talari HR
        • Rafiee M
        • Farrokhian A
        • et al.
        The effects of folate supplementation on carotid intima-media thickness and metabolic status in patients with metabolic syndrome.
        Ann Nutr Metab. 2016; 69: 41-50
        • Ma F
        • Wu T
        • Zhao J
        • et al.
        Folic acid supplementation improves cognitive function by reducing the levels of peripheral inflammatory cytokines in elderly Chinese subjects with MCI.
        Sci Rep. 2016; 6: 1-11
        • Mangoni AA
        • Arya R
        • Ford E
        • et al.
        Effects of folic acid supplementation on inflammatory and thrombogenic markers in chronic smokers. A randomised controlled trial.
        Thromb Res. 2003; 110: 13-17
        • Spoelstra-de Man A
        • Brouwer C
        • Terheggen F
        • Bollen J
        • Stehouwer C
        • Smulders Y.
        No effect of folic acid on markers of endothelial dysfunction or inflammation in patients with type 2 diabetes mellitus and mild hyperhomocysteinaemia.
        Neth J Med. 2004; 62: 246-253
        • Durga J
        • Van Tits L
        • Schouten EG
        • Kok FJ
        • Verhoef P.
        Effect of lowering of homocysteine levels on inflammatory markers: a randomized controlled trial.
        Arch Intern Med. 2005; 165: 1388-1394
        • Klerk M
        • Durga J
        • Schouten EG
        • Kluft C
        • Kok FJ
        • Verhoef P.
        No effect of folic acid supplementation in the course of 1 year on haemostasis markers and C-reactive protein in older adults.
        Thromb Haemost. 2005; 94: 96-100
        • Title LM
        • Ur E
        • Giddens K
        • McQueen MJ
        • Nassar BA.
        Folic acid improves endothelial dysfunction in type 2 diabetes—an effect independent of homocysteine-lowering.
        Vasc Med. 2006; 11: 101-109
        • Sato S
        • Tajiri Y
        • Nakayama H
        • Yamada K.
        Folic acid supplementation of aspirin therapy further improves vascular endothelial function among patients with type 2 diabetes: a short-term crossover study.
        Diabetol Int. 2015; 6: 284-289
        • Rajdl D
        • Racek J
        • Trefil L
        • Stehlik P
        • Dobra J
        • Babuska V.
        Effect of folic acid, betaine, vitamin B6, and vitamin B12 on homocysteine and dimethylglycine levels in middle-aged men drinking white wine.
        Nutrients. 2016; 8: 34
        • Satapathy S
        • Bandyopadhyay D
        • Patro BK
        • Khan S
        • Naik S.
        Folic acid and vitamin B12 supplementation in subjects with type 2 diabetes mellitus: a multi-arm randomized controlled clinical trial.
        Complement Ther Med. 2020; 53102526
        • Fatahi S
        • Pezeshki M
        • Mousavi S
        • et al.
        Effects of folic acid supplementation on C-reactive protein: a systematic review and meta-analysis of randomized controlled trials.
        Nutr Metab Cardiovasc Dis. 2019; 29: 432-439
        • Moens AL
        • Claeys MJ
        • Wuyts FL
        • et al.
        Effect of folic acid on endothelial function following acute myocardial infarction.
        Am J Cardiol. 2007; 99: 476-481
        • Moher D
        • Liberati A
        • Tetzlaff J
        • Altman DG.
        Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement.
        Ann Intern Med. 2009; 151 (w264): 264-269
        • Higgins JP
        • Thomas J
        • Chandler J
        • et al.
        Cochrane handbook for systematic reviews of interventions.
        John Wiley & Sons, 2019
        • DerSimonian R
        • Laird N.
        Meta-analysis in clinical trials.
        Control Clin Trials. 1986; 7: 177-188
        • Borenstein M
        • Hedges LV
        • Higgins JP
        • Rothstein HR.
        Introduction to meta-analysis.
        John Wiley & Sons, 2021
      1. Fedorov S. GetData Graph Digitizer version 2.24. Available at www. getdata-graph-digitizer. com.2002.

        • Higgins JP
        • Thompson SG.
        Quantifying heterogeneity in a meta-analysis.
        Stat Med. 2002; 21: 1539-1558
        • Fan J
        • Gijbels I.
        Local polynomial modelling and its applications: monographs on statistics and applied probability.
        Routledge, 2018: 66
        • Mousavi SM
        • Jayedi A
        • Bagheri A
        • et al.
        What is the influence of cinnamon supplementation on liver enzymes? A systematic review and meta-analysis of randomized controlled trials.
        Phytother Res. 2021; 35: 5634-5646
        • Karimi E
        • Bitarafan S
        • Mousavi SM
        • et al.
        The effect of vitamin D supplementation on fibroblast growth factor-23 in patients with chronic kidney disease: A systematic review and meta-analysis.
        Phytother Res. 2021;
        • Egger M
        • Smith GD
        • Schneider M
        • Minder C.
        Bias in meta-analysis detected by a simple, graphical test.
        BMJ. 1997; 315: 629-634
        • Asemi Z
        • Vahedpoor Z
        • Jamilian M
        • Bahmani F
        • Esmaillzadeh A.
        Effects of long-term folate supplementation on metabolic status and regression of cervical intraepithelial neoplasia: a randomized, double-blind, placebo-controlled trial.
        Nutrition. 2016; 32: 681-686
        • Chen H
        • Liu S
        • Ji L
        • et al.
        Folic acid supplementation mitigates Alzheimer's disease by reducing inflammation: a randomized controlled trial.
        Mediators Inflamm. 2016; (2016)
        • Ma F
        • Zhou X
        • Li Q
        • et al.
        Effects of Folic Acid and vitamin B12, alone and in combination on cognitive function and inflammatory factors in the elderly with mild cognitive impairment: a single-blind experimental design.
        Curr Alzheimer Res. 2019; 16: 622-632
        • Guyatt G
        • Oxman AD
        • Akl EA
        • et al.
        GRADE guidelines: 1. Introduction—GRADE evidence profiles and summary of findings tables.
        J Clin Epidemiol. 2011; 64: 383-394
        • Kim J
        • Kim H
        • Roh H
        • Kwon Y.
        Causes of hyperhomocysteinemia and its pathological significance.
        Arch Pharm Res. 2018; 41: 372-383
        • Lazzerini PE
        • Capecchi PL
        • Selvi E
        • et al.
        Hyperhomocysteinemia, inflammation and autoimmunity.
        Autoimmunity Rev. 2007; 6: 503-509
        • Balint B
        • Jepchumba VK
        • Guéant J-L
        • Guéant-Rodriguez R-M
        Mechanisms of homocysteine-induced damage to the endothelial, medial and adventitial layers of the arterial wall.
        Biochimie. 2020; 173: 100-106
        • Schroecksnadel K
        • Frick B
        • Wirleitner B
        • Winkler C
        • Schennach H
        • Fuchs D.
        Moderate hyperhomocysteinemia and immune activation.
        Curr Pharm Biotechnol. 2004; 5: 107-118
        • Li W
        • Ma Y
        • Li Z
        • et al.
        Folic acid decreases astrocyte apoptosis by preventing oxidative stress-induced telomere attrition.
        Int J Mol Sci. 2020; 21: 62
        • Pravenec M
        • Kožich V
        • Krijt J
        • et al.
        Folate deficiency is associated with oxidative stress, increased blood pressure, and insulin resistance in spontaneously hypertensive rats.
        Am J Hypertens. 2013; 26: 135-140
        • Conzade R
        • Koenig W
        • Heier M
        • et al.
        Prevalence and predictors of subclinical micronutrient deficiency in German older adults: results from the population-based KORA-age study.
        Nutrients. 2017; 9: 1276