October 9, 2017Neurology
According to a study published in JAMA Neurology (7 August 2017), a large, long-term study suggests that middle aged Americans who have vascular health risk factors, including diabetes, high blood pressure and smoking, have a greater chance of suffering from dementia later in life.
The study was partially funded by NIH's National Institute of Neurological Disorders and Stroke (NINDS), which also created the Mind Your Risks® public health campaign to make people more aware of the link between cardiovascular and brain health. The study analyzed the data of 15,744 people who participated in the Atherosclerosis Risk in Communities (ARIC) study. From 1987-1989, the participants, who were black or white and 45-64 years of age, underwent a battery of medical tests during their initial examinations at one of four centers in four different states. Over the next 25 years they were examined four more times. Cognitive tests of memory and thinking were administered during all but the first and third exams. Results showed that 1,516 participants were diagnosed with dementia during an average of 23 follow-up years. Initially, when the authors analyzed the influence of factors recorded during the first exams, they found that the chances of dementia increased most strongly with age followed by the presence of APOE4, a gene associated with Alzheimer's disease. Caucasian Americans with one copy of the APOE4 gene had a greater chance of dementia than African Americans. Other factors included race and education: African Americans had higher chance of dementia than Caucasian Americans; those who did not graduate from high school were also at higher risk. In agreement with previous studies, an analysis of vascular risk factors showed that participants who had diabetes or high blood pressure, also called hypertension, had a higher chance of developing dementia. In fact, diabetes was almost as strong a predictor of dementia as the presence of the APOE4 gene. Unlike other studies, the authors discovered a link between dementia and prehypertension, a condition in which blood pressure levels are higher than normal but lower than hypertension. Also, race did not influence the association between dementia and the vascular risk factors they identified. Diabetes, hypertension and prehypertension increased the chances of dementia for white and black participants. Finally, smoking cigarettes exclusively increased the chances of dementia for Caucasian Americans but not African Americans.
Further analysis strengthened the idea that the vascular risk factors identified in this study were linked to dementia. For instance, in order to answer the question of whether having a stroke, which is also associated with the presence of vascular risk factors, may explain these findings, the team reanalyzed the data of participants who did not have a stroke and found similar results. Diabetes, hypertension, prehypertension and smoking increased the risk of dementia for both stroke-free participants and those who had a stroke.
Recently, in a separate study, the authors analyzed brain scans from a subgroup of ARIC participants who did not have dementia when they entered the study (JAMA: 11 April 2017). Results showed that the presence of one or more vascular risk factors during midlife was associated with higher levels of beta amyloid, a protein that often accumulates in the brains of Alzheimer's patients. This relationship was not affected by the presence of the APOE4 gene and not seen for risk factors present in later life. The presence of vascular risk factors detected in participants older than 65 years of age during the final examination was not associated with greater levels of beta amyloid.
In the future, the authors plan to investigate ways in which subclinical, or undiagnosed, vascular problems may influence the brain and why race is associated with dementia.