Sixteen RCTs (n=19,501) were included.
The median quality score of the included studies was 4 (range: 3 to 5). The studies were clinically heterogeneous with respect to interventions, follow-up times, patient age, and degree or duration of hypertension. There was highly significant heterogeneity between the studies in most (5 out of 6) meta-analyses for the outcome of BP reduction (I-squared 97.0 to 98.6%).
Four RCTS (n=13,212) assessed the effect of BP pressure reduction on MMSE after a mean of 17.7 months’ treatment. Three studies were pooled and showed a WMD in BP of -4.8/-2.6 mmHg between the two study arms, which was associated with a statistically significant improvement in the intervention arm in mean MMSE score (WMD 0.19, 95% CI: 0.19, 0.19). The fourth study (n=69) was excluded from analysis because of heterogeneity.
Five RCTs (n=717) assessed the effect of BP reduction on logical memory after a mean of 5.2 months’ treatment. The pooled studies showed a WMD in BP of -3.2/-1.5 mmHg between the two study arms, which was associated with a statistically significant improvement in the intervention arm in immediate (WMD 0.62, 95% CI: 0.21, 1.02) and delayed (WMD 0.67, 95% CI: 0.23, 1.11) scores for logical memory tasks.
Four RCTs (n=2,396) assessed the effect of BP reduction on perceptual processing and sequencing, using the trail making test (TMT)-A after a mean of 18.3 months’ treatment. The pooled studies showed a WMD in BP of -17.1/-7.0 mmHg between the two study arms, which was associated with a significant decline in trail making performance in the intervention arm (WMD -1.12 seconds, 95% CI: -1.22, -1.02).
Three RCTs (n=2,184) assessed the effect of BP reduction on paired associate learning. The pooled studies showed a WMD in BP of -17.1/-7.0 mmHg between the two study arms, which was associated with a significant decline in performance in the intervention arm (WMD –0.04 seconds, 95% CI: -0.04, -0.04).
One RCT (n=351) investigated digit span, symbol digit substitution and the TMT-B, but there was no significant reduction in BP in the intervention group and no change in cognitive performance.