Low-dose aspirin may help some people lower their risk of developing colon cancer, but not if they wait until age 70 to start, a large study published in JAMA Oncology suggests. Researchers found that when people began using aspirin in their 50s or 60s, their risk of developing colon cancer after age 70 was reduced by 20%. There was no such benefit, however, among those who began using aspirin at age 70 or later. The findings are based on more than 94,500 healthcare professionals who were followed since the 1980s. During that time, 1,431 were diagnosed with colon cancer. On average, people who had regularly used aspirin were 20% less likely to develop colon cancer at age 70 or older, after accounting for factors like diet, exercise levels, smoking, and body weight. The benefit, however, was apparent only among people who had started aspirin before age 70. The findings make sense, said Dr. David Greenwald, a gastroenterologist and professor at Mount Sinai’s Icahn School of Medicine in New York City. There is evidence, he said, that it takes 10 to 20 years of aspirin use to lower the risk of colon cancer. “I think this implies that in people who start in their 70s, you don’t have enough time to see a benefit,” said Dr. Greenwald, who was not involved in the study.