Those of us past age 40 are generally familiar with those first glimmerings of forgetfulness and muddled thinking. We cant easily recall peoples names, certain words, or where we left the car keys.
Its what we scientists call having a CRS problem, said David R Jacobs, a professor of public health at the University of Minnesota in Minneapolis and a co-author of the new study.
But these slight, midlife declines in thinking skills strike some people later or less severely than others, and scientists have not known why. Genetics almost certainly play a role, most researchers agree. Yet the contribution of lifestyle, and in particular of exercise habits, has been unclear.
So recently, Dr Jacobs and colleagues from universities in the United States and overseas turned to a large trove of data collected over several decades for the Cardia study. The study, whose name is short for Coronary Artery Risk Development in Young Adults, began in the mid-1980s with the recruitment of thousands of men and women then ages 18 to 30 who underwent health testing to determine their cholesterol levels, blood pressure and other measures.
Many of the volunteers also completed a treadmill run to exhaustion, during which they strode at an increasingly brisk pace until they could go no farther. The average time to exhaustion among these young adults was 10 minutes, meaning that most were moderately but not tremendously fit.
Twenty-five years later, several thousand of the original volunteers, now ages 43 to 54, were asked to repeat their treadmill run. Most quit much sooner now, with their running times generally lasting seven minutes or less, although a few ran longer in middle age than they had as relative youngsters.
Then, the volunteers completed a battery of cognitive tests intended to measure their memory and executive function, which is the ability to make speedy, accurate judgments and decisions.(The participants did not undergo similar memory tests in their 20s.)
The results, published last month in Neurology, are both notable and sobering. Those volunteers who had managed to run for more than 10 minutes before quitting generally performed best on the cognitive tests in middle age. For every additional minute that someone had been able to run as a young adult, he or she could usually remember about one additional word from the lists and make one fewer mistake.
That difference in performance, obviously, is slight, but represents about a years worth of difference in what most scientists would consider normal brain ageing, Dr Jacobs said.
So the 50-year-old who could remember one word more than his age-matched fellows would be presumed to have the brain of a 49-year-old, a bonus that potentially could be magnified later, Dr Jacobs added. In essence, the findings suggest that the ability to think well in middle age depends to a surprisingly large degree on your lifestyle as a young adult.
It looks like the roots of cognitive decline go back decades, Dr Jacobs said.
Which would be a bummer for anyone who spent his or her early adulthood in happy, heedless physical sloth, if the scientists hadnt also found that those few of their volunteers who had improved their aerobic fitness in the intervening years now performed better on the cognitive tests than those whose fitness had remained about the same or declined.
Its a clich, but it really is never too late to start exercising, Dr Jacobs said, if you wish to sharpen your thinking skills.