Genetic changes can predict cancer up to 13 years in the future, according to new research.

Harvard and Northwestern University discovered that tiny but significant changes are already happening in the body more than a decade before cancer is diagnosed.

They found that the protective caps on the ends of chromosomes, which prevent DNA damage, had significantly more wear and tear in people who went on to develop cancer. In fact, in some cases they looked 15 years older.

Those caps, known as telomeres, were much shorter than they should be and continued to get shorter until around four years before the cancer developed, when they suddenly stopped shrinking. All the people with the changes went on to develop cancer.