Does size matter? In many things it does. As far as brain size though, there is some debate about that. First you have to look at size within a specific species. Some species of birds are very smart, but have tiny brains. Bird brain isn’t always an insult. Perhaps rather than size, it should be looked at as brain size relative to body size? That is called the encephalization quotient and it’s a mathematical theory that takes ratios of brain size and body size and attempts to link them in predicting cognition. No studies have shown definitively though that brain size is correlated to intelligence.
Recent research has shown however that physical fitness and brain size are linked according to a study published in the February 10, 2016, online issue of Neurology,
the medical journal of the American Academy of Neurology, individuals who are in poor physical shape during middle age might wind up having less brain volume later in life..
Study author Nicole Spartano, PhD, with Boston University School of Medicine in Boston used participants enrolled in the Framingham Heart Study
. 1,583 people with an average age of 40 and without dementia or heart disease, got on treadmills and had their physical fitness measured. Two decades later, there was another treadmill test as well as MRI scans of their brains.
As a result of some of the testing, certain participants were found to have developed heart disease or high blood pressure and those individuals were evaluated separately within the study. These study participants were evaluated for fitness and found to have an exercise capacity of 39ml/kg/min. This is a numerical expression of how much oxygen the body can use in one minute. The participants were instructed to stay on the treadmill until their heart rate reached a certain level, much like a cardiac stress test. The longer they could exercise on the treadmill, the greater their exercise capacity and overall fitness. The separate evaluation of those with heart issues was significant to how the results were interpreted.
The study results
showed that for every eight units lower a person performed on the treadmill test, their brain volume two decades later was smaller, equivalent to two years of accelerated brain aging. The numbers were adjusted to reflect the heart disease group and those results were that for every eight units of lower physical performance there was an associated reduction of brain volume equal to one year of accelerated brain aging.
The study also showed that people whose blood pressure and heart rate went up at a higher rate during exercise also were more likely to have smaller brain volumes two decades later. A higher heart rate or BP during the test is an indicator of a lower level of physical fitness.
Spartano stressed that the study did not find any causal relationship between poor physical fitness and lower brain volume, it simply showed an association between the two. In a press release from AAN
, she said, “While not yet studied on a large scale, these results suggest that fitness in middle age may be particularly important for the many millions of people around the world who already have evidence of heart disease.”
Check out the video below to learn more about the study and what it could mean in future neurological and cardiac research.