The quality o evidence is downgraded by study limitations (lack of reporting or dropout rates associated with older age or worse cognitive function at baseline; a large proportion of participants ended studies on a different treatment to which they had been initially randomised) and by indirectess (study durations were too short to expect a significant difference in dementia rates).
A Cochrane review [Abstract] 1 included 12 studies with a total of 30 412 subjects with hypertension to assess whether pharmacological treatment of hypertension can prevent cognitive impairment or dementia in people who have no history of cerebrovascular disease. Eight studies compared active treatment with placebo, 2 sudies compared intensive versus standard blood pressure reduction, and 2 studies compared different classes of antihypertensive drug. Study durations varied from 1 to 5 years and most participants were middle-aged or older.
There was no difference in the incidence of dementia between treatment and placebo groups (236/7767 versus 259/7660, OR 0.89, 95% CI 0.72 to 1.09; 4 studies, n=15 427). There was a modest benefit from antihypertensive treatment compared to placebo as evaluated by change in MMSE (MD 0.20, 95% CI 0.10 to 0.29; 4 studies, n=9 435). Both systolic and diastolic blood pressure levels were reduced significantly (MD -9.25 mmHg, 95% CI -9.73 to -8.78 for systolic blood pressure, MD -2.47 mmHg, 95% CI -2.70 to -2.24 for diastolic blood pressure).
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