Heart disease has naturally received particular attention from genetics researchers, since it kills more people worldwide than any other disease. In the past few years, geneticists have isolated a number of gene variations that are strongly associated with serious heart conditions and can be pinpointed with genetic testing.
But providing people with genetic information suggesting that their hearts are menaced without also offering them possible ways to stave off that threat seems callous.
Thankfully, some past studies have hinted that people’s lifestyles, including how they eat and exercise, can ease even strong inherited risks for heart problems.
But most such studies have examined a range of lifestyle issues.
For the new study, which was published this month in Circulation, researchers at Stanford University and other institutions decided to focus specifically on the role of physical fitness.
Because they also wanted to include a large and varying group of people in the study, they turned to the trove of data gathered in Britain in the U.K. Biobank, which houses health information about more than 500,000 men and women who were between ages 40 and 69 at the study’s start in 2006.
All of the participants had provided blood and saliva samples for genetic testing, filled out extensive questionnaires about their exercise and other health habits, and in some cases, sweated on a stationary bike or treadmill and later squeezed a vise-like gadget to quantify their aerobic fitness and muscular strength. Some also wore activity monitors for a week to objectively track how much they moved.
The researchers zeroed in on the 482,702 men and women in the study who had had no known heart disease at the start, genetically typing their tissue samples, looking for various snippets of genes known to raise heart disease risk. They also stratified them into three groups, based on how fit and strong they were.
Then they checked to see whether any of the men and women developed heart disease within the next six years or so. Many did, according to their health records, especially if they carried any of the gene variants associated with cardiac conditions.
But physical fitness changed that calculus significantly, the data showed.
Those men and women with the highest aerobic fitness halved their statistical likelihood of developing heart disease, no matter how worrisome their genetic profiles, the scientists found.
In essence, if people were fit, they were less likely to have heart problems than someone who was less fit, even if their genes predicted heart disease.
Stout grip strength likewise reduced cardiac-disease risk, although not quite to the same extent.
“What this tells us is that you can mitigate some of your genetic risk for heart disease by being fit, no matter how high that risk may be,” says Dr. Erik Ingelsson, a professor of medicine at Stanford who oversaw the study.
The data intimate, too, that the amount of fitness required is not huge. The people in the high-fitness group “were not athletes,” Dr. Ingelsson says. They engaged in moderate activities, like walking, according to their activity questionnaires.
The study can’t tell us, though, precisely how much we need to exercise to get the best protection against genetic heart disease, he says, because the number of people who wore fitness trackers was too small for such determinations.
It also is an associational study, meaning that it shows links between higher fitness and lower disease risk. But it cannot prove that one caused the other.
Perhaps most intriguing, the study raises a raft of new questions about the complicated interplay of genes, environment and lifestyles. Like heart disease risk, aerobic fitness and muscular strength each can be affected by genetic inheritance, Dr. Ingelsson says, and certain gene variants involved in physical fitness might alter the workings of other variants affecting heart disease risk, or vice versa, even before someone hits the sidewalk for a brisk walk.
Diet, smoking, weight and other aspects of health and lifestyle can also change how some genes affect other genes. Dr. Ingelsson and his colleagues are delving into many of these issues in upcoming experiments, he says.
But for now, he concludes, for optimal heart health, “This study reinforces what we already knew, which is that we should be physically active.”