People often look to exercise to keep their hearts fit and their weight down, but a new study says that fitness is the key to keeping your immune system young and healthy—but only if you’re active for a lifetime. The study was published today in the journal Aging Cell.

Related: Exercise can help an aging heart no matter how old you are

We already know that regular exercise reduces risk of diseases associated with aging, like cardiovascular problems. But scientists from the University of Birmingham, in the U.K., and King’s College London wanted to see how much healthier people who exercised their entire lives really are.

The research team enlisted 125 people between 55 and 79 years old who bicycled for fun. Male cyclists were able to complete 62 miles in less than 6.5 hours while females had to log 37 miles in 5.5 hours. People who smoked, drank heavily or had other health problems were not included. The researchers measured markers of health, such as blood pressure, muscle mass, cholesterol and T cells, which are important in keeping our immune systems healthy. Then the team compared the results from the lifetime exercisers to 75 healthy people between the ages of 57 and 88, as well as 55 young adults between the ages of 20 and 36.

They found that a lifetime of exercise helped people maintain muscle mass and lower body fat and cholesterol. Not only that, but people who regularly hit the gym had the immune systems of much younger adults. 

Study co-author Stephen Harridge, an expert in human physiology at King’s College London, believes that the same group of participants would not enjoy the same health benefits without exercise.



“Their bodies have been allowed to age optimally, free from the problems usually caused by inactivity. Remove the activity and their health would likely deteriorate,” Harridge said in a statement.  

Now might be a good time to go for that run.