A systematic review including 10 cohort studies (494,804 men and 54,832 women), 28 published RCTs (52,350 men), and two international studies (number of participants were not given) were abstracted in DARE.
Cohort studies: Relative risks in subgroup with lowest cholesterol concentration compared with the rest of the cohort were as follows: circulatory disease (not IHD) employed men 0.92; circulatory disease, community setting 1.12; cancer employed men 1.00, community setting 1.23 (significant); accidents & suicides employed men 0.95, community setting 1.29 (significant); other diseases employed men 1.08, community setting 1.62 (significant); all causes except IHD employed men 1.00, community setting 1.20 (significant).
Randomised controlled trials: Odds ratio for reduction in cholesterol concentration of 0.6 mmol/l: circulatory disease (not IHD) 1.00; cancer 1.07; accidents & suicides 1.17; other 1.07, all causes except IHD 1.07. The 95% CIs of these odds ratios all include 1. According to the randomised trials, the relative risk of death in treated/control groups per 0.6 mmol/l (10%) reduction in cholesterol was 1.06 (95% CI 0.97 to 1.17) in subjects without IHD, and 0.90 (95% CI 0.84 to 0.97) in subjects with IHD.
Comment: The quality of evidence is downgraded by inconsistency of results.