Lead author on the following study, BrightFocus researcher Kristine Yaffe, MD, is well known for her research into cognition and aging. She’s received Bright Focus Alzheimer’s Disease Research funding support since 2012 for her studies relating diabetes to cognition.
A group of researchers based at the University of California, San Francisco (UCSF), have shown that when cardiovascular risk factors (CVRF) such as elevated glucose and high blood pressure begin in early adulthood, they are associated with significantly worse cognitive function in middle age compared with having no CVRF.
The study by researcher Kristine Yaffe, MD, et al, was published online in Circulation on March 31, 2014. Dr. Yaffe is professor of psychiatry and neurology at UCSF, and is supported by BrightFocus.
The team analyzed data from several thousand 18- to 30-year-olds enrolled in the Coronary Artery Risk Development in Young Adults (CARDIA) study. That study began in 1985 and followed subjects for 25 years. Every two to 5 years, they had a medical evaluation and their cardiac risks were assessed. After 25 years, they were assessed for cognitive function using three standardized tests.
The results showed that:
- Those whose blood pressure and glucose levels exceeded recommended levels during the 25-year study displayed performed worse on three standard tests that measure executive function, cognitive processing speed, and verbal memory.
- The association with lower cognitive function was small, but statistically significant, for most of the CVRF.
- High cholesterol was associated only with poor verbal memory.
Why Is This Study Important?
Previous studies have demonstrated there is a strong connection between cardiovascular health and brain health.
However, whereas most previous evidence is linked to events in later life—i.e., the development of Alzheimer’s disease or another form of dementia in old age following cardiovascular risks seen in mid-life ), this study is one of the first to investigate the effects of early life CVRF on cognitive function in midlife (i.e., at age 50 or thereabouts). And even though the effects seen in this middle-aged study population are mild, evidence is strong based on a large sample and cumulative exposure to CVRF over 25 years.
In a press release, Dr. Yaffe was quoted: “We already know that reducing these risk factors in midlife can decrease the risk of dementia in old age. If it turns out that the damage begins before middle age, we may need to work on reducing heart disease risks in earlier stages of life”—i.e., in young adulthood.
Since cognitive function was not measured at the beginning of the study, the investigators were not able to estimate exactly how much cognitive function was lost in the group with CVRF. “We can say that almost for sure they don’t have dementia,” Dr. Yaffe said in an interview with The Washington Post about the study.
However, “the fact that we’re able to see [the association] so early is kind of amazing, and it’s kind of sobering and exciting,” she said.
Questions You May Have About This Study
Q. Is the lower cognitive functioning measured in the group with higher CVRFs a sign of the onset of Alzheimer’s disease?
A. That’s impossible to say for sure. Even though this study lasted 25 years, subjects were still only middle aged when it ended. Only in relatively rare cases of familial (or “early onset”) Alzheimer’s disease would they be diagnosed that young; most people don’t begin to experience symptoms until they are 60-70 years old. And the study was not designed to diagnose Alzheimer’s disease, only to reflect cognitive functioning. Still, Yaffe and colleagues think there’s a very good chance that cardiac risk factors may contribute to the risk of developing Alzheimer’s disease.
Q. Do the results show that cardiovascular disease causes Alzheimer’s disease?
A. Scientists are still figuring out what causes AD, but it’s unlikely that cardiovascular disease is a direct cause. Instead, as with most diseases associated with aging, there’s probably an interplay of genetic and environmental factors. Cardiovascular risk, which by itself can be partially inherited, may represent one of the “environmental risks,” or stressors, acting on neurons. Luckily, it is also a condition that can be greatly improved by lifestyle factors including good nutrition, exercise, a low-fat diet, no smoking, and good ways of handling and reducing stress.
When cardiac risks go uncontrolled, Yaffe and other scientists have speculated about how that might contribute to Alzheimer’s disease. For example, poor circulation may lead to a reduced blood supply to the brain; this in turn might cause changes in the brain structure that lead to increased inflammation and oxidative stress, which damage neurons. Another possibility is that cardiac risk factors bring about biochemical changes in the blood and brain that makes it more difficult to remove amyloid protein “plaque”—a waste material associated with Alzheimer’s disease. Over time and in larger quantities, these plaques may become toxic to brain tissue, triggering the death of neurons and the start of Alzheimer’s symptoms.
Even though we haven’t figured out all the answers to Alzheimer’s disease, it’s clear that prevention has a role to play. In fact, in an earlier epidemiologic study, Dr. Yaffe and Deborah E. Barnes, PhD, MPH, projected that seven modifiable risk factors are responsible for up to half of all cases, and that targeted interventions to achieve a 10-25% reduction in those risk factors would have a huge impact, potentially preventing millions of cases in the United States and worldwide (Barnes D and Yaffe K, Lancet Neurol., 2011). Those seven risk factors are diabetes, mid-life hypertension and obesity, smoking, depression, low educational attainment, and physical inactivity.
Q. What do the results mean?
A. From this and earlier studies, there’s a growing body of evidence showing that cognitive health risks accumulate across our lives. This study and others would suggest that young adults should maintain a healthy weight and active lifestyle and reduce their cardiovascular risks as early as possible in life—and that taking steps to do so is important for brain health, just as it is for heart health.
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