Table 1

Summary of results of each component

ComponentNumber and type of meta-analyses
(reference)
Grade of overall certainty of evidenceOverall effect on colorectal cancer incidenceRange of the effect* (if significant)
Components with protective effect on CRC risk
 Aspirin4 Observational,9–12 1 RCT,14 1 mixed13 ⨁⨁⨁◯
Moderate
(serious inconsistency and suspected publication bias)
Protective−14% to −29%
 Low-dose aspirin2 Observational,10 12 1 RCT13 ⨁⨁◯◯
Low
(serious inconsistency and suspected publication bias)
Protective (observational)
No effect in RCT
 NSAIDs3 Observational
10 15 16
⨁⨁◯◯
Low
(serious inconsistency and suspected publication bias)
Protective−27% to −43%
 Magnesium3 Observational17–19⨁⨁◯◯
Low
Protective−11% to −22%
 Folic acid3 Observational20–22 ⨁◯◯◯
Very low
(serious inconsistency and indirectness, strong suspected publication bias)
Protective−12% to −15%
 Folic acid combination2 RCT,23 24 1 mixed25 ⨁◯◯◯
Very low
(very serious indirectness)
No effectNA
 Dairy products3 Observational26–28 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
Protective/no effect−13% to −19%
 Fibre5 Observational26 29–32 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
Protective effect (4) no effect (1)−22% to −43%
 Fruits and vegetables9 Observational26 30 33–39 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
Protective effect (5) no effect (4)−8% to −52%
 Soy3 Observational38–40 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
Protective (2)/no effect (1)−8% to −15%
Components with no effect on CRC risk
 Vitamin E5 RCT,41–45 2 observational21 22 ⨁⨁◯◯
Low
(serious indirectness)
No effect (6)/protective (1 Obs)−12%
 Vitamin C2 Observational,21 22 1 RCT44 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
No effectNA
 Antioxidant combinations4 RCT,41 42 44 45 1 observational21 ⨁◯◯◯
Very low
(very serious indirectness)
No effect (4)/protective (one obs, vitamin C combination)−17%
 β-Carotene3 RCT42 45 46 ⨁⨁⨁◯ Moderate
(serious inconsistency)
No effectNA
 β-Carotene combinations5 RCT42 44–47 ⨁◯◯◯
Very low
(very serious indirectness)
No effectNA
 Selenium3 RCT42 44 45 ⨁⨁⨁◯ ModerateNo effectNA
 Tea5 Observational26 48–51 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
No effect (4)/protective effect (1)−18%
 Garlic and allium4 Observational21 52–54 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
No effect/protective (1)−24%
 Vitamin D3 Observational,21 22 56 1 RCT55 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
No effect/Protective (2 Obs)−12% to −13%
 Vitamin D+calcium2 RCT55 57 ⨁◯◯◯
Very low
(very serious indirectness)
No effectNA
Components with unclear effect on CRC risk
 Coffee7 Observational26 58–63 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
No effect (4)/protective effect (3)−17% to −24%
 Fish and omega-37 Observational26 33 64–68 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
No effect (4)/Protective (3)−7% to −13%
 Calcium3 Observational,21 72 73 2 RCT70 71 ⨁◯◯◯
Very Low
(serious inconsistency and serious indirectness, serious imprecision)
Protective (observational)
No effect or increased risk (RCT)
Protective: −14% to −24%
Increased
+7%
 Vitamin A2 Observational21 22 ⨁⨁◯◯
Low
(very serious indirectness)
Protective (1)/no effect (1)
 Group B vitamins2 Observational22 69 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
Protective (1)/no effect (1)−10% (Vitamin B6)
 Statins6 Mixed,76–81 1 RCT,74 1 observational75 ⨁⨁◯◯
Low
(serious inconsistency and serious indirectness)
Unclear−6% to −14%
Components associated with increased CRC risk
 Meat7 Observational26 33 39 82–85 ⨁◯◯◯
Very low
(serious inconsistency and very serious indirectness)
Increased risk+12% to +21%
 Alcohol9 Observational86–94 ⨁◯◯◯
Very low
(serious inconsistency and indirectness, strong suspected publication bias)
Increased risk+12% to +20%
  • CRC, colorectal cancer; NA, Not applicable; NSAID, non-steroidal anti-inflammatory drug; RCT, randomised clinical trial.