Cardiorespiratory Fitness and Alzheimer’s Disease

A recent study reported in the journal Neurology once again gives us more evidence about how important exercise may be for keeping your brain healthy.

The study looked at how fit two groups were. One group included people without memory problems and had an average age of about 72 years. The second group included people with Mild Cognitive Impairment and early Alzheimer’s disease. Their average age was about 74 years (this difference wasn’t statistically significant). Both groups included about the same number of men and women and were well-educated (many had at least some college-level education).

The researchers looked a measure of how well the lungs can use oxygen that’s referred to as “VO2 max.” It’s an index of how well the heart and the lungs work during exercise.

They looked at the brains of people in each group using magnetic resonance imaging (MRI). From this, they could calculate how big several parts of the brain were.

They gave all the participants a battery of neuropsychological measures that assessed their thinking and memory abilities.

The researchers showed that for the people with memory problems (those with mild cognitive impairment and early Alzheimer’s disease) there was a relationship between fitness and how big the brains of the patients were. People who were more fit had bigger brains. They had more gray matter – that’s the part of the brain that includes nerve cells. (White matter has the fibers that connect the parts of the gray matter.)

For the people who didn’t have memory problems, there wasn’t a relationship between the size of the brain and fitness. But in this group, there was a relation between fitness and how well they did on the neuropsychological tests.

This study shows two things that are important. First, it confirms that people who are more fit do better on test of memory and other thinking skills. Since other studies have shown this, this isn’t new. Second, it shows that the size of the gray matter in the brain in people with early stages of memory loss is related to fitness. This is new, and gives us a clue about why physical fitness might be related to brain fitness.

One warning: like many studies about risk factors and memory loss, this study is only looks at the way two things are related. Researchers call this kind of study correlational, because it looks at the relation between two things using a statistical measure called correlation. It’s important to remember that in this kind of study, we don’t know which way the two things are related.

It may be that better fitness causes people to have more nerve cells. On the other hand, it may be that people with more nerve cells exercise more. So although this study continues to emphasize the importance of fitness, we should interpret it with a little bit of caution.

The study appeared in the journal Neurology, 71, 210-216 (July 15, 2008)