TABLE F.1 Data from the most recent and complete systematic reviews and meta‐analyses on each type of cancer.
| Reference | Cancer type | Exposure variable | Eligible designs | Search | N eligible studies | Pooled estimate a | Results of individual studies (highest vs. lowest) a |
|---|---|---|---|---|---|---|---|
| Fu et al. (2021) | Incident pancreatic cancer | Folate intake and P/S folate | PCs, NCCs and CCs |
Pubmed and eMBASe databases Until November 2019 |
7 PCs + 3 NCCs [8 assessed dietary folate intake and 2 P/S folate] | RR (highest vs. lowest) = 0.85, 95% CI: 0.66–1.09, p = 0.244; I 2 61.8% | Positive associations in two studies (Schernhammer et al., 2007) (RRQ4 vs. Q1 1.34 (0.79, 2.26), Q4 > 17.4 nmol/L vs. Q1 < 14.9 nmol/L) and (Keszei et al., 2009) (RRQ5 vs. Q1 1.37 (0.97, 1.94), Q5 > 259.1 μg/day vs. Q1 < 176.3 μg/day total folate); null or negative associations in other studies |
| Liu et al. (2017) | Incident oesophageal cancer | Folate intake and P/S folate | Cohort studies and CCs |
Pubmed, MEDLINE and EMBASE Until May 2017 |
2 PCs [1 assessed dietary folate intake and 1 S folate] | OR (highest vs. lowest) = 0.82, 95% CI: 0.57–1.07; I 2 51.4% | Null or negative associations in all studies |
| Liu et al. (2017) | Incident gastric cancer | Folate intake and P/S folate | Cohort studies and CCs |
Pubmed, MEDLINE and EMBASE Until May 2017 |
5 PCs [4 assessed dietary folate intake and 1 S folate] | OR (highest vs. lowest) = 0.97, 95%CI:0.80–1.13; I 2 0.0% | Null or negative associations in all studies |
| Ren et al. (2020) | Incident breast cancer | Folate intake and P/S folate | PCs and CCs |
Pubmed and eMBASe databases Until April 2019 |
19 PCs on folate intake 2 PCs on P/S folate |
Folate intake OR (highest vs. lowest) = 0.97, 95% CI: 0.91–1.03; p = 0.003; I 2 53.3% S folate OR (highest vs. lowest) = 1.63, 95% CI: 0.61–4.37; p = 0.078; I 2 67.% |
Positive association in one study (OR Q5 vs. Q1 4.11 (0.84, 20.18), Q5 > 63 nmol/L vs. Q1 ≤14 nmol/L) (Kim et al., 2016); null or negative associations in other studies |
| Zhang et al. (2014) | Incident lung cancer | Folate intake | PCs and NCCs |
PubMed, Embase and the Cochrane Library Until September 2013 |
9 PCs | RR (highest vs. lowest) = 0.92; 95% CI: 0.84–1.01; p = 0.076; I 2 0.0% |
Positive association in one study (HRQ5 vs. Q1 1.12 (0.83, 1.52) for Q5 > 374 vs. Q1 ≤237 μg/day natural folate) (Kabat et al., 2008); null or negative associations in other studies |
| Wang, Zhang, and Yang (2021) | Incident ovarian cancer | Folate intake | CCs, cross‐sectional or cohort studies |
PubMed, Web of Science, Embase, Cochrane and Wanfang databases Until May 2020 |
4 PCs on dietary folate intake 4 PCs on total folate intake |
Total folate intake (including FS) RR (highest vs. lowest) = 1.21, 95% CI: 0.89–1.65; I2 40.8% |
Null or negative associations in all studies |
| Du et al. (2016) | Incident endometrial cancer | Folate intake | PCs, NCCs, CCs |
PubMed, Embase and Web of Science Search date NR |
5 PCs | OR (highest vs. lowest) = 1.05, 95% CI: 0.90–1.20; I 2 = 19.8% | Positive association for type II but not type I endometrial cancer in one study (ORQ4 vs. Q1 1.71 (0.87, 3.36), Q4 > 560 vs. Q1 < 250 μg/day total folate) (Uccella et al., 2011); null or negative associations in other studies |
| Gu et al. (2022) | Urothelial carcinoma | Folate intake and P/S folate | PCs, NCCs, CCs |
Pubmed and eMBASe databases Until October 2019 |
8 PCs +2 NCCs [9 assessed dietary folate intake and 1 plasma folate] | RR (highest vs. lowest) = 0.97, 95% CI: 0.87–1.09, p = 0.638; I 2 0% | Positive associations in two studies (Bassett et al., 2019) (RRQ5 vs. Q1 1.27, 95% CI 0.81, 2.00; <9.3 vs. >17.0 nmol/L) and (Michaud et al., 2002) (RRQ5 vs. Q1 1.16, 95% CI 0.82, 1.64; median Q1 257.3 vs. Q5 400.2 μg/day natural folate); null or negative associations in other studies |
| Hezaveh et al. (2021) | Incidence of non‐melanoma skin cancer (BCC, SCC or both) or overall skin cancer | Folate intake | Cohort studies and CCs |
Scopus, ISI Web of Science and PubMed From 2000 to July 2021 |
4 PCs | Not pooled (few studies and heterogeneous) | Positive association in two studies with BCC risk (RR positive in all quintiles vs. Q1 < 284 μg/day total folate, RRQ5 vs. Q1 1.19, 95% CI 1.01, 1.40 (van Dam et al., 2000); positive in all quintiles versus Q1, median Q1 208 μg/day total folate, RRQ5 vs. Q1: 1.2 95% CI:1.1–1.3 (Fung et al. 2002). Positive association with overall skin cancer (HR positive for T2 and T3 vs. T1, T1 mean 222 μg DFE/day total folate, HRT3 vs. T1: 1.79; 95% CI: 1.07, 2.99 (Donnenfeld et al., 2015). No association with SCC in one study (Fung et al., 2003) |
Abbreviations: BCC, basal cell carcinoma; CCs, case–control studies; CI, confidence interval; FS, food supplements; NCCs, nested case–control studies; OR, odd ratio; PCs, prospective cohort studies; P/S, plasma/serum; RR, relative risk; SCC, squamous cell carcinoma.
Results for case–control and cross‐sectional designs not extracted.