We all know that exercise is good for the body and the mind. But if you're a senior, more is not necessarily better. A study published recently says just 'a little' exercise can do a lot of good for the aging brain.

Researchers at the University of Kansas Alzheimer's Disease Center recruited more than 100 sedentary adults age 65 and up. The seniors had to be healthy and have no symptoms of dementia.  The researchers assigned them to one of four groups.  One group did moderate exercise for 150 minutes per week, which is the amount currently recommended.  A second group did half that -- 75 minutes a week -- and a third did 225 minutes per week or 50 percent more than currently recommended.  The exercise consisted of brisk treadmill walks (some did elliptical) for 25 minutes to an hour -- all supervised by personnel at a local YMCA. A fourth group was instructed to just do their usual exercise.

Before the study began and again after 26 weeks, researchers tested the participants for their aerobic capacity, their memory and their ability to think.  The more participants exercised, the more their aerobic capacity or endurance increased. The ones who did 225 minutes a week were the fittest of all, which was not a surprise to the researchers. But when it came to cognitive performance -- the thinking and memory testing -- the results weren't so clear cut.  All the seniors who started exercising could think better. But those who did 75 minutes a week did just as well as those who sweated it out for 225 minutes a week.

A different study by researchers at Boston University School of Medicine found that a hormone called irisin is secreted during exercise. Irisin is produced in the brain during endurance exercise. The hormone is believed to protect the brain from damage. The researchers were able to correlate blood hormone levels from aerobic fitness, and identify positive effects on memory function linked to exercise.  As well, aerobic exercise improves the ability of the heart to pump blood to the vital organs, including the brain, and improves the circulation of blood within the brain itself.  Exercise lowers the risk of depression, which is associated with memory and cognitive decline.

In University of Kansas study, when the seniors exercised, their attentiveness to everything from conversations to what was going on around them went up.  Their ability to process visual signals also increased.  That is what allows people to figure out what's important to notice in their field of vision. Both attentiveness and visual processing increased with exercise. Both are important parts of what's known as executive function or management of thought processes, including working memory, reasoning, mental flexibility and problem solving, as well as planning and execution. Executive function goes down in the years prior to the onset of dementia.

The more seniors exercise, the better their endurance or stamina and the greater the impact on their heart and lungs. But when it comes to brain power, more exercise is not necessarily better.  The good news is that you don't need to overtrain to get the cognitive or brain benefits from exercise.  It doesn't matter how much or how many minutes a week you exercise.  As long as you train enough to increase your peak 'V02'   --  the maximum volume of oxygen (ml/kg/min) that a senior can use --  then your memory and thinking will improve.  

This is one more reason why all of us -- especially seniors -- should make vigorous exercise part of our daily routine. You have everything to gain and little to lose, starting today.

Dr. Brian Goldman hosts White Coat Black Art, which returns with new episodes beginning Saturday, September 12 on CBC Radio One.  Watch this blog for a big announcement about our new time slots.  Dr. Goldman is also the author of The Secret Language of Doctors.