Studies that have explored the links between circulation problems and cognitive decline have tended to focus on conditions that affect the blood supply to the brain, such as stroke.
Few of these earlier studies, however, have looked at the long-term links between incident coronary heart disease (CHD), such as heart attack and angina, and cognitive decline.
Narrow arteries reduce blood supply
CHD, or coronary artery disease, can develop when the arteries that feed the heart become narrow and obstruct blood flow.
The arteries become narrow because fatty deposits, or plaques, build up inside their walls. Medical professionals call this process atherosclerosis.
The reduction in blood flow causes heart muscle to receive less oxygen, increasing the likelihood of a heart attack. The reduction in blood supply can also cause chest pain, or angina.
CHD is the leading cause of death worldwide, according to the World Health Organization (WHO). In 2016, it was responsible for more than 9 million deaths.
Xie and his colleagues believe that their study is one of the largest to investigate cognitive decline in the years before and after receiving a diagnosis of CHD.
Their analysis took in data from 7,888 participants, aged 50 and older, from the English Longitudinal Study of Aging (ELSA).
The recent Journal of the American College of Cardiology study is unique; it tracked cognitive decline both before and after incident CHD.
"Incident CHD," its authors conclude, "is associated with accelerated cognitive decline after, but not before, the event."
They suggest that the findings highlight the long-term relationship between cognitive decline and CHD.
Lead and corresponding study author Wuxiang Xie, Ph.D., says that because there is not yet a cure for dementia, it is important to detect and treat the brain condition as early as possible in order to delay its progression.
"Even small differences in cognitive function can result in an increased risk of dementia in the long-term," explains Xie, who holds research posts at Peking University Clinical Research Institute in China and in the School of Public Health at Imperial College London in the United Kingdom.
CHD and cognitive decline
The ELSA collected data twice per year between 2002 and 2017. None of the participants had a history of heart attack, angina, or stroke or a diagnosis of dementia or Alzheimer's disease at the start of the study period.
The researchers excluded people who did not complete all the cognitive assessments or who had a stroke during the median follow-up of 12 years.
Over the follow-up period, the participants underwent three tests of cognitive function, which the researchers conducted in eight waves. The tests assessed verbal memory, semantic fluency, and sense of time, or "temporal orientation."
During the study period, 5.6% of the participants experienced angina or heart attacks. Everyone in this group demonstrated a more rapid decline in cognitive function in the three tests compared with those who did not experience a CHD event.
The study authors note that they "found that incident CHD was significantly associated with faster rates of post-CHD-diagnosis cognitive decline, but not with cognitive changes in the years before or short-term changes following the event."
Speculating on the findings, they suggest that the reduction in oxygen to the brain is the likely reason for the link between CHD and faster cognitive decline.
Previous research linked CHD to interruptions of blood supply to the brain, or cerebral microinfarcts. Such links suggest that CHD might promote small vessel disease, which is a major contributor to dementia in older adults.