A newly published study finds that exercising in older age can help keep one's immune system active and young.

Researchers in Britain followed 125 cyclists over the age of 55 and found that they had immune systems of 20-year-olds.

The researchers found these cyclists have higher levels of freshly made T-cells, which play an important role in one's immune response, such as recognizing and killing foreign invaders.

Professor Janet Lord, director of the Institute of Inflammation and Ageing at the University of Birmingham and a co-author of the study, said "the immune system declines by about 2-3 percent a year from our 20s, which is why older people are more susceptible to infections, conditions like rheumatoid arthritis and, potentially, cancer."

The research was published in the journal Aging Cell.