Patients with high BP had a 6.5% greater reduction in cognitive function in later life than people with normal BP, the study published in JAMA Neurology found.
Researchers said although the reduction was 'modest', the increased risk of dementia meant it 'significantly' raised the public health burden of hypertension.
The study found no link between later-life hypertension and cognitive decline, suggesting that addressing BP in midlife was a more important target for preventing cognitive problems.
The study, led by researchers at the Johns Hopkins University School of Medicine in Baltimore, Maryland, is among the strongest evidence yet of a link between the conditions.
Researchers looked at data from 13,476 participants, followed up for 23.5 years as part of the Atherosclerosis Risk in Communities study.
Further evidence of a link
Participants with normal BP at the beginning of the study experienced an average decline of 0.840 global cognitive z score points, compared with a decline of 0.896 points for people with hypertension.
People with high BP who used medication had less cognitive decline than participants with untreated hypertension.
The researchers said: 'Although we note a relatively modest additional [cognitive] decline associated with hypertension, lower cognitive performance increases the risk for future dementia, and a shift in the distribution of cognitive scores, even to this degree, is enough to increase the public health burden of hypertension and prehypertension significantly.
'Initiating treatment in late life might be too late to prevent this important shift. Epidemiological data, including our own study, support midlife BP as a more important predictor of – and possibly target for prevention of – late-life cognitive function than is later-life BP.'
Dr Simon Ridley, head of research at Alzheimer’s Research UK, said: 'This large-scale, long-term study adds further weight to an evidence base linking high BP to a risk of cognitive decline. Although this research is not able to establish cause and effect, a large body of research suggests that what is good for the heart is also good for the brain.'