A joint Australian and US study has found fluctuating blood pressure is an indicator of cognitive decline and dementia in older people.

Fluctuations in high blood pressure in older adults, particularly in men, is associated with an increased risk of dementia and cognitive decline.

A new report using data from the long-term ASPREE study, involving Monash University, could help identify people who are at increased risk of major cognitive impairment and point the way towards prevention and new areas for research.

The new paper is one of many findings from the ASPREE (ASPirin in Reducing Events in the Elderly) dataset.

The primary prevention aspirin trial released its results to global acclaim in 2018. It found aspirin reduced non-fatal and fatal cardiovascular events in patients with a history of symptomatic cardiovascular disease, and the benefits of aspirin outweighed the increased risk of bleeding.

Further analysis of the data from 19,114 Australians and Americans, continues to deliver new findings in healthy older adults, mostly over the age of 70.

The study was co-led by Associate Professor Joanne Ryan from the Monash School of Public Health and Preventive Medicine and Professor Mike Ernst from the University of Iowa.

By 2050 it's believed that people 60 years and older will outnumber adolescents and youths.

"As an age-related disease, and one with a notable lack of treatments, dementia will indefinitely remain a major public health priority," Assoc Prof Ryan said.

"Any opportunity to identify early those at risk, and engage people in preventive therapies, is important."

Hypertension - systemic high blood pressure - in mid-life has previously been shown to be a strong predictor of dementia in later life. More recently, data has shown that short and long-term fluctuations in blood pressure are also an indicator of cognitive decline.

Associate Professor Ryan said data from 16,758 ASPREE participants who underwent standardised blood pressure and cognition assessments and received long-term follow up were used in the study.

Those in the highest BPV group were found to be at significantly increased risk of incident dementia and cognitive decline compared with those in the lowest BPV group. Being male also increased the risk significantly.

It also found those at risk included older, relatively healthy adults who had reached late life without significant cognitive impairment - a group that is not typically considered at high risk for dementia.

The results also provide the first evidence of possible sex-specific effects of BPV on cognition.

Men have a higher lifetime exposure than women to other known risk factors of cognitive decline, such as uncontrolled high blood pressure and smoking. But even when the researchers accounted for those, the increased risk for men remained.

"While we don't know for sure, it is tempting to speculate about the existence of different pathways towards cognitive decline in men and women. Or sex hormones such as oestrogen across a woman's lifetime may have a protective effect for women," Assoc Prof Ryan said.

"More study is warranted into this area to help determine the underlying reasons for these sex-specific differences, and into research to find out whether reducing BPV can preserve late-life cognitive function."

The paper is published in the Journal of the American Heart Association.