Six randomised controlled trials (n=6,300) were included in the review.
For all-cause mortality, the RRs for each of the individual studies ranged from 0.5 (95% CI: 0.2, 1.1, p=0.08) to 1.0 (95% CI: 0.3, 3.0, p>0.99), suggesting that the numbers were too small in the individual studies to determine an impact.
The results of the homogeneity test (p=0.7) indicated that the results were homogeneous across the studies.
The pooled RR was 0.82 (95% CI: 0.7, 0.99. p=0.03). The data suggested that aspirin reduces the risk of death by approximately 20% in the studied population. The ARRs ranged from 2.0% (plus or minus 3.1%) at the 12-month follow-up, to 8.7% (plus or minus 6.3%) at the 20-month follow-up.
Across all outcomes, the ARRs ranged from 0.9% (plus or minus 3.7%) at the 52-month follow-up, to 18.6% (plus or minus 7.7%) at the 3-month follow-up.
The pooled RR was 0.7 (95% CI: 0.6, 0.8) for vascular events and 0.7 (95% CI: 0.6, 0.8) for MI. Significant heterogeneity was found in both of these results (p<0.001).
Five of the 6 studies reported GI bleeding, which was a rare find: only 58 cases were reported, approximately half of which were severe enough to require withdrawal. There were no reported deaths related to GI bleeding, and GI bleeding led to almost no permanent morbidity. Only one study demonstrated a statistically-significant increased risk of GI bleeding as a result of aspirin intake. The analysis of GI bleeding across all studies suggested a pooled risk ratio of 2.5% (95% CI: 1.4, 4.7, p=0.001). No significant heterogeneity was found (P=0.5).
Only 2 of the 6 included studies reported cases of haemorrhagic stroke; the results were therefore not conclusive, although the pooled RR from the 2 homogeneous (P>0.99) studies was 0.8 (95% CI: 0.7, 1.0). Based on the number-needed-to-treat with aspirin to either prevent one death or cause one GI bleeding event, it was determined that 1.5 deaths could be prevented for every nonfatal GI bleeding attributed to the use of aspirin.