Reference Study Country Duration Funding	Design	Subject characteristics at baselinea	Interventiona	Endpoint assessed	Results
Cole et al. (2007) AFPPS USA 3 yrs + 3–5 yrs (trial follow‐up with continued folic acid treatment) Enrolment 1994–98 Fortification started 1996, and was mandatory 1998 Public, Supplements by private company	RCT 3 × 2 factorial design, with folic acid and aspirin Inclusion criteria: 21–80 yrs and histologically confirmed adenoma removed. Each participant had a complete colonoscopy, with removal of all known polyps, within 3 mo of enrolment. Exclusion criteria: familial polyposis syndromes, intestine cancer, malabsorption syndromes, condition worsened by supplemental aspirin or folic acid, conditions treated with aspirin, non‐steroidal anti‐inflammatory drugs or folate. Cobalamin deficient individuals were excluded. N participants randomised/completed 1st follow‐up/completed 2nd follow‐up/Consented continue folic acid or placebo/analysed 2nd follow‐up G1: 516/501/475/370/303 G1a: 175/NR/NR/NR/NR G1b: 171/NR/NR/NR/NR G1c: 170/NR/NR/NR/NR G2: 505/486/451/359/304 G2a: 169/NR/NR/NR/NR G2b: 167/NR/NR/NR/NR G2c: 169/NR/NR/NR/NR	Sex (% women) G1: 36% G2: 36.4% Age G1: 57 ± 9.6 G2: 57 ± 9.5 Nutrient status marker (ng/mL) G1: P‐folate 10.5 ± 7.9 G2: P‐folate 10.4 ± 7.5 No other relevant sources of heterogeneity	Folic Acid Doses 1st follow‐up (3 years) G1: 1000 μg /day G1a: 1000 μg/day + 81 mg/day aspirin G1b: 1000 μg/day + 325 mg/day aspirin G1c: 1000 μg/day + aspirin placebo 2nd follow‐up (+ 3–5 years) G2: Placebo G2a: Placebo +81 mg/day aspirin G2b: Placebo +325 mg/day aspirin G2c: Placebo + aspirin placebo Background nutrient intake: dietary folate G1: 320 ± 147 G2: 325 ± 163 Compliance: Reported adherence ‘excellent’ 87% ≥6 d/week during 1st interval 71% ≥6 day/week during 2nd interval Similar across treatments	Colonoscopy at the end of the initial 3‐year intervention (1st follow‐up) and at the end of the 2nd follow‐up (completed by 1 October 2004). Primary outcome: at least 1 colorectal adenoma. Secondary outcomes: advanced lesions (tubulovillous adenomas [25%–75% villous features], villous adenomas ≥75% villous features], large adenomas [≥1 cm in diameter], adenomas with high‐grade dysplasia or invasive cancer), adenoma multiplicity (0, 1–2 or ≥3 adenomas).	Primary outcome: at least 1 colorectal adenoma 1st follow‐up G1: 44.1%, 221/501 G2: 42.4%, 206/486 uRR 1.04 (95% CI 0.90–1.20) 2nd follow‐up G1: 41.9%, 127/303 G2: 37.2%, 113/304 uRR 1.13 (95% CI 0.93–1.37) Both follow‐ups (n = 607) G1: 71.3% G2: 65.5% uRR 1.09 (95% CI 0.98–1.21) Multivariable‐adjusted RR were similar (NR). No significant effect modification by sex, age, alcohol, smoking, plasma folate, BMI, presence/absence of advanced lesions); no significant interaction Folic acid/aspirin. However, the suggested increased risk for folic acid was confined to participants not allocated to aspirin. Secondary outcomes: advanced lesions 1st follow‐up G1: 11.4% 57/501 G2: 8.6% 42/486 uRR 1.32 (95% CI 0.90–1.92) 2nd follow‐up G1: 11.6% 35/303 G2: 9.6% 21/304 uRR 1.67 (95% CI 1.00–2.80) Both follow‐ups G1: 23.1% G2: 17.1% uRR 1.35 (95% CI 0.98–1.86) Secondary outcome: ≥3 lesions 1st follow‐up G1: 9.4% 47/501 G2: 7.8% 38/486 uRR 1.20 (95% CI 0.80–1.81) 2nd follow‐up G1: 9.9% 30/303 G2: 4.3% 13/304 uRR 2.32 (95% CI 1.23–4.35) Results were similar when the analysis was restricted to the 501 participants who agreed to extended treatment with folic acid or placebo in the second follow‐up interval
Passarelli et al. (2019) AFPPS As of above but with additional post‐treatment follow‐up from Oct 1st, 2004 to May 31st 2012	As of above As compared to the 2007 publication, and because the study was terminated Oct 2004 due to funding, some colonoscopies were scheduled after that date and thus not included. In the 2019 paper, a total 218 additional colonoscopies were performed (after Oct 2004) of which 161 had agreed to continue treatment (G1 or G2). This was still the 2nd follow‐up. Aspirin treatment ended after the first endoscopy follow‐up (i.e. 3 yrs)	As of above	As of above	Colonoscopy at the end of the initial 3‐year intervention (1st follow‐up) and at the end of the 2nd follow‐up (until the intended end of the second interval). Primary outcome: at least 1 colorectal neoplastic lesion (i.e. conventional adenomas, sessile serrated adenomas/polyps (SSA/Ps) and invasive CRC). Secondary outcomes: advanced conventional adenomas (tubulovillous or villous adenomas, or ≥1 cm in diameter, or with high‐grade dysplasia or CRC), ≥3 conventional adenomas, and SSA/Ps.	Relative risk adjusted for age, sex, centre, race, BMI, smoking, family history of CRC, number of advanced adenomas on examination qualifying, for study entry (all at baseline). 1st follow‐up Any conventional adenoma, SSA/P, CRC G1: 44% (221/501) G2: 42% (206/486) Relative Risk 1.04 (95% CI 0.90–1.21) Advanced conventional adenomas, CRC G1: 10% (48/501) G2: 9% (43/486) Relative Risk 1.00 (95% CI 0.66–1.52) ≥3 conventional adenomas, CRC G1:6% (30/501) G2: 6% (27/486) Relative Risk 1.12 (95% CI 0.65–1.94) SSA/P G1: 12% (60/501) G2: 9% (44/486) Relative Risk 1.41 (95% CI 0.96–2.08) 2nd follow‐up Any conventional adenoma, SSA/P, CRC G1: 43% (146/338) G2: 36% (118/325) Relative Risk 1.21 (95% CI 0.99–1.47) Advanced conventional adenomas, CRC G1: 9% (32/338) G2: 8% (27/325) Relative Risk 1.20 (95% CI 0.73–1.97) ≥3 conventional adenomas, CRC G1:9% (30/338) G2: 5% (16/325) Relative Risk 1.58 (95% CI 0.87–2.86) SSA/P G1: 8% (28/338) G2: 5% (16/325) Relative Risk 1.94 (95% CI 1.02–3.68)
Logan et al. (2008) UkCAP 9 UK, 1 DK centers Recruitment 1997–2001 3 yrs Public	RCT 2 × 2 factorial design with Folic acid, aspirin Inclusion criteria: <75 yrs of age, CR adenoma > = 0.5 cm removed 6 mo before randomisation. Exclusion: medical conditions hindering participation N participants randomised/completed 2nd colonoscopy/completed both meds: G1: 234/215/161 G2: 236/217/149 G3: 236/217/159 G4: 233/204/158	Sex (% women) G1: 48.7% G2: 45.8% G3: 39% G4: 39.1% Age: mean 57.8 yr (range 27.6–74.6 yr) Nutrient status marker: NR	Folic acid Doses: G1: 500 μg folic acid per day G2: 300 mg aspirin per day G3: 500 μg folic acid +300 mg aspirin per day G4: Placebo Background folate intake: (μg/day) G1: 309 ± 126 G2: 311 ± 108 G3: 312 ± 107 G4: 298 ± 105 Those with ≥95% Folate Compliance in those with 2nd coloscopy were: G1 & G3: 80% G2 & G4: 81%	Colonoscopy Any adenomas (%)/ advanced adenomas (%), no of outcome adenomas/participant (mean) Advanced adenomas: adenomas ≥1 cm in diameter	Those who completed 2nd colonoscopy per single treatment group % with any adenomas/% with advanced adenomas/No. of adenomas per patient (mean) G1: 30.2/15.4/0.48 G2: 22.6/10.1/0.33 G3: 23/8.8/0.29 G4: 27.5/14.7/0.42 Main effect folic acid treatment according to: Any adenomas n (%)/Advanced adenomas n (%) G1 & G3 (folate): 115 (26.6)/52 (12) vs. G2 & G4 (no folate): 105 (24.9)/52 (12.4) Relative Risk (RR) (95% CI): RR = 1.07 (0.85–1.34) for any adenomas RR = 0.98 (0.68–1.40) for advanced adenomas
Wu et al. (2009) HPFS & NHS Folic acid prevention trial USA 3–6.5 yrs; 1996–2004 Fortification started 1996, i.e. post‐ fortification era Public, supplements from private	RCT Inclusion/exclusion criteria: NHS & HPFS participants who had a history of CR adenoma confirmed by medical record, planned another endoscopy 4 y after initiation of trial, agreed not to take multivitamins, cancer free at randomisation except for early‐stage prostate or breast cancer or non‐melanoma skin cancer. Only included non‐cobalamin deficient (defined as, 200 pg/mL or as 200–299 pg/mL with methylmalonic acid concentrations >32 lg/L). Ineligible if presently taking multivitamin, folic acid or vitamin B‐12 supplements for a diagnosed vitamin deficiency or had homocysteinemia or pernicious anaemia, gastrectomy or gastrointestinal disorder or other illnesses N participants randomised/completed colonoscopy/analysed G1: 338/NR/237 G2: 334/NR/238 49% agreed to extend treatment from 3 yrs to 5–6.5 yrs	Sex (% women) G1: 62% G2: 63% Age G1: 64.5 ± 6.9 G2: 65.5 ± 6.3 Baseline P‐folate (ng/mL): G1: 9.2 ± NR G2: 9.1 ± NR No major baseline differences between treatments and between randomised and those having a colonoscopy (i.e. 475 out of 672 participants) Baseline P‐folate (ng/mL) for those who donated blood samples twice (see next column: G1: 9.7 ± 6.8 G2: 9.3 ± 6.2	Folic acid Doses: G1: 1000 μg/day G2: Placebo Background folate intake (μg/day) G1: 323 G2: 324 Compliance: 77% performed adherence P‐folate at midtrial: G1: 39.2 ± 24.8 ng/mL G2: 17.0 ± 7.9 ng/mL, reasonable pill compliance for those who donated two blood samples	Colonoscopy performed by their physician ≥3 mo after initiation and ≤12 after trial completion. Primary outcome: any new (recurrent) adenoma Secondary outcome: adenoma by site and stage and number	At least 1 adenoma/total G1: n = 62/237 G2: n = 72/238 Risk Ratio (RR): 0.87 (95% CI 0.65–1.16) Advanced adenoma/total (please note not all adenomas were classified according to advanced or early) G1: n = 16/221 G2: n = 14/225 Risk Ratio (RR): 1.03 (95% CI 0.53–1.98) Stratified analyses: By baseline P‐folate ≤7.5 ng/mL RR 0.61 (95% CI 0.42–0.90) >7.5 ng/mL RR 1.28 (95% CI 0.82–1.99) By combination alcohol intake (g/d)/P‐folate ≤5.6 g/day and >7.5 ng/mL RR 1.23 (95% CI 0.64, 2.37) >5.6 g/day and ≤7.5 ng/mL RR 0.49 (95% CI 0.28, 0.84) p = 0.009
Jaszewski et al. (2008) USA 3 yrs Dec 1998‐ June 2005 NR	RCT Inclusion criteria: 18–80 yrs and had a colonoscopy and had at least one adenoma Exclusion: severe co‐morbid conditions, heart disease, cancer or other organ dysfunction or contraindications for colonoscopy/polypectomy. Gastrointestinal disorders affecting absorption/metabolism of folic acid, cobalamin deficiency and hereditary CRC. Pregnant or lactating women. Patients who drank more than 2 alcoholic drinks daily or who were regularly using vitamin, minerals, steroids and non‐steroidal anti‐inflammatory drugs (excluding aspirin for CVD prevention), antineoplastic agents or folate. N participants invited/ eligible of polyp histology and run‐in compliance/completed colonoscopy 3 yrs later G1: 80/NR/46 G2: 97/NR/48	Sex (% women) G1: 7% G2: 8% Age G1: 60 ± 10 G2: 63 ± 10 S‐folate ng/mL G1: 14.53 ± 19.51 G2: 11.35 ± 6.65 RBC‐folate ng/mL G1: 447 ± 165 G2: 478 ± 149	Folic acid Doses: G1: 5000 μg/day G2: Placebo Folate intake μg/day G1: 184 ± 232 G2: 162 ± 140 Compliance: Pill count and telephone contact every 90 days (NR). Participants were required to take 90% of their pills.	Colonoscopy at 3‐y follow‐up (all identified polyps)	Number of adenomas/patient G1: 0.36 +/− 0.69 G2: 0.82 +/− 1.17 p = 0.02514 Number of hyperplastic polyps/patient G1: 0.44 +/− 0.89 G2: 0.51 +/− 0.94 NS Advanced adenomas or Left‐sided p < 0.02 for both outcomes in favour of folic acid, and folic acid was more protective in those <70 yr

Abbreviations: AFPPS, Aspirin/Folate Polyp Prevention Study; BMI, body mass index; CI, confidence Interval; CR, colorectal; CRC, colorectal cancer; CVD, cardiovascular disease; d, day(s); DK, Denmark; G, group; HPFS, Health Professionals Follow‐Up Study; mo, months; NHS, Nurses' Health Study; NR, not reported; p, plasma; RBC, red blood cells; RCT, randomised controlled trial; S, serum; SD, standard deviation; SSA/P, sessile serrated adenomas/polyps; U, unadjusted; UK, United Kingdom; ukCAP, United Kingdom Colorectal Adenoma Prevention; yr, year.