Middle–aged people with risk factors for heart attacks and stroke are also more likely to develop changes in the brain that can lead to Alzheimer's disease, a new study suggests.

Previous research has linked so–called vascular risk factors, including obesity, diabetes, smoking, high cholesterol and elevated blood pressure, to higher odds of dementia, cognitive decline and Alzheimer’s disease.

But it’s been unclear whether these factors contribute indirectly by restricting blood flow in the brain, or if they directly cause a buildup of amyloid protein fragments that are linked to Alzheimer’s.

“In our study, we found an association between the number of risk factors that people without dementia had when they were middle–aged and the risk of having amyloid in their brain when they were older,” said lead study author Dr. Rebecca Gottesman of Johns Hopkins University School of Medicine in Baltimore.

“Each alone may not be enough to increase the risk of Alzheimer’s disease, but having a number of these risk factors appears to be associated with an even higher risk,” Gottesman said by email. “Although this doesn’t prove causation, it suggests that vascular risk factors might directly impact Alzheimer’s changes in the brain.”

Alzheimer’s disease is the most common cause of dementia among older adults. Scientists suspect that changes in the brain begin at least a decade before symptoms appear.

For the current study, researchers examined data from 346 adults who had been evaluated for vascular risk factors since the late 1980s, when they were 52 years old on average and none of them had dementia. More than two decades later, when participants were around 76 years old, they had brain scans that looked for evidence of Alzheimer’s.

At the start of the study, 1 in 5 participants had no vascular risk factors, while 38% had one and 42% had at least two.

A higher number of vascular risk factors in midlife, but not in late life, was associated with elevated brain amyloid, researchers report in JAMA.

Brain scans found that 31% of people with no vascular risk factors at the start of the study had elevated amyloid later in life, compared with 61% of the people who had at least two vascular risk factors in middle age.

Relationships between vascular risk factors and brain amyloid didn’t differ by race. There also wasn’t a meaningful difference based on whether people were carriers of what’s known as the ApoE4 allele, a version of a gene that’s associated with increased risk for Alzheimer’s disease.

“Brain amyloid is a risk factor that likely begins prior to the development of memory problems and thus, these findings are very intriguing,” Dr. Jeffrey Burns, co–director of the University of Kansas Alzheimer’s Disease Center in Kansas City, said by email. “We do need to be careful to recognize that amyloid in the brain does not equal Alzheimer’s disease.”

It’s possible that brain vascular disease might either lead to an increase in amyloid deposits or a decreased ability to remove amyloid that accumulates. But the study wasn’t designed to answer this question, Dr. Andrew Budson, a neurology researcher at The VA Boston Healthcare System and Boston University School of Medicine who wasn’t involved in the study, said by email.

Still, the results add to the evidence suggesting that people who focus on heart health earlier in life may also be safeguarding their brains, said Dr. Hannah Gardener, a neurology researcher at the University of Miami who wasn’t involved in the study.

“Patients and physicians need to work together to monitor and minimize the burden of vascular health factors like smoking, obesity, blood pressure, cholesterol and diabetes with the goal of protecting both heart and brain health decades before Alzheimer’s disease typically manifests,” Gardener said by email.

—Lisa Rapaport