OK, it’s unsurprising that fit people have fewer heart events than those who are out of shape, but a new study by researchers at Stanford University gives us the numbers: people with the highest aerobic fitness have half as much heart disease as less fit people, even if their genetic profile points to high cardiac risk. The New York Times reports that the researchers used data from the U.K. Biobank, which tracked health information, starting in 2006, of more than 500,000 men and women between ages 40 and 69. The researchers focused on people who had had no known heart disease at the start, looking for genes that are associated with heart disease risk, and also dividing the cohort into three groups based on strength and fitness. When, over the next six years, they tracked those who developed heart disease, they found that men and women with the highest aerobic fitness cut their statistical likelihood of developing heart disease in half, regardless of the risk suggested by their genes. A strong grip was associated with better heart health, although to a lesser degree than general fitness. The Times reports that the study raises new questions about the interplay of genes, environment and lifestyles, because, after all, aerobic fitness and muscular strength, like heart disease, are influenced by our genes.