What is the association between PM and cancer incidence?
The IARC assessed more than 800 observational studies investigating the association between PM and cancer incidence. In this evaluation, the greatest weight of evidence was given to prospective cohorts investigating CRC. One such study was by Bernstein et al. (2015) who conducted a large cohort consisting of 47, 389 American men and 87,108 American women investigating the association between PM and CRC. The Hierarchy of Evidence (H.O.E.) suggests cohorts have consistently strong results supported by strong evidence (Ho et al., 2008). However, the study conducted by Bernstein et al did not produce strong evidence that supports their concluding statement that PM intake is positively associated with colon cancer. This association may be unreliable as the confidence intervals are very wide and may be invalid (HR 1.36, 95% 1.09-1.69).
Additionally, Bernstein based his findings on servings of meat per day; variations in serving size across different types of meat may impact the reliability of results. In fact, only a limited number of cohorts examining the direct impact of a dose (g) response relationship between PMs and cancer incidence were included in the IARC evaluation. One of these studies was by Larrson et al (2006) who reported consuming more than 30g of PMs daily was associated with increased risk of CRC. This dose response relationship may be of greater accuracy than ‘servings per day’ reflected by narrower confidence intervals (1.09 (95% CI = 1.05-1.13).