Recommendation grade [A, B, C, D, E] and level of evidence [I, II-1, II-2, II-3, III, good, fair, poor] are indicated after each recommendation. Definitions for these grades and levels are repeated following the recommendations.
The Canadian Task Force on Preventive Health Care (CTFPHC) concludes that there is insufficient evidence to recommend for or against the use of routine vitamin E supplementation for the primary prevention of cardiovascular disease (CVD) events in the general population and in male smokers (Grade I recommendation) ("MRC/BHF Heart Protection Study," 2002 [I, good]; de Gaetano, 2001 [I, fair]; Virtamo et al., 1998 [I, fair]).
The CTFPHC concludes that there is good evidence to recommend against the use of vitamin E for the secondary prevention of CVD in patients with established CVD or risk factors for CVD (Grade D recommendation) ("MRC/BHF Heart Protection Study," 2002 [I, good]; Yusuf et al., 2000 [I, good]; Virtamo et al., 1998 [I, fair]; Rapola et al., 1997 [I, fair]; "Dietary supplementation," 1999 [I, fair]; Stephens, et al. 1996 [I, fair]).
The CTFPHC concludes that there is good evidence to recommend against the use of routine vitamin E supplementation for the prevention of lung cancer (Grade D recommendation), ("The effect of vitamin E," 1994 [I, good]; "MRC/BHF Heart Protection Study," 2002 [I, good]).
The CTFPHC concludes that there is insufficient evidence to recommend for or against the use of routine vitamin E supplementation for the prevention of cancers in the general population (Grade I recommendation), ("MRC/BHF Heart Protection Study," 2002 [I, good];"The effect of vitamin E," 1994 [I, fair]; Blot et al. 1993 [I, fair]; Albanes et al., 2000 [I, fair]; Virtamo et al., 2000 [I, fair]; Heinonen et al., 1998 [I, fair]).
Definitions:
Levels of Evidence - Research Design Rating
Research Design Rating
I: Evidence from at least one randomized controlled trial (RCT)
II-1: Evidence from controlled trial(s) without randomization
II-2: Evidence from cohort or case-control analytic studies, preferably from more than one centre or research group
II-3: Evidence from comparisons between times or places with or without the intervention; dramatic results in uncontrolled experiments could also be included here
III: Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees
Quality (Internal Validity) Rating
Good: A study that meets all design-specific criteria* well.
Fair: A study that does not meet (or it is not clear that it meets) at least one design-specific criterion* but has no known "fatal flaw."
Poor: A study that has at least one design-specific* "fatal flaw," or an accumulation of lesser flaws to the extent that the results of the study are not deemed able to inform recommendations.
*General design-specific criteria are outlined in Harris RP, Helfand M, Woolf SH, Lohr KN, Mulrow CD, Teutsch SM, Atkins D. Current Methods of the U.S. Preventive Services Task Force: A Review of the Process. Am J Prev Med 2001;20(suppl 3):21-35.
Recommendations Grades for Specific Clinical Preventive Actions
A: The Canadian Task Force (CTF) concludes that there is good evidence to recommend the clinical preventive action.
B: The CTF concludes that there is fair evidence to recommend the clinical preventive action.
C: The CTF concludes that the existing evidence is conflicting and does not allow making a recommendation for or against use of the clinical preventive action; however, other factors may influence decision-making.
D: The CTF concludes that there is fair evidence to recommend against the clinical preventive action.
E: The CTF concludes that there is good evidence to recommend against the clinical preventive action.
I: The CTF concludes that there is insufficient evidence (in quantity and/or quality) to make a recommendation; however, other factors may influence decision-making.
