Dr. Peter Rothwell of Oxford University and the John Radcliffe hospital, and colleagues, said it is time to add prevention of cancer into the analysis of the balance of risk and benefits of aspirin. So far, all the guidelines have just been based on the prevention of strokes and heart attacks.
"This research really shows that the cancer benefit is as large, if not larger, than the benefit in terms of preventing heart attacks and strokes," he told the Guardian. "It does change the equation quite drastically."
All the data for the studies came from 51 trials giving low-dose aspirin to people at risk of a heart attack or stroke. Aspirin thins the blood, making it less likely to clot.
The first study showed a daily low-dose pill for three years could reduce risk of cancer by 23 percent for men and 25 percent for women. The risk of dying of cancer was cut by 15 percent, but the risk was reduced to 37 percent for those who take aspirin for longer than five years.
The second study found aspirin helped prevent the spread of cancer -- metastasis -- to other organs by 48 percent.
Aspirin also reduced the risk of being diagnosed with a solid cancer that had already spread by 31 percent, the third study said.
The findings are scheduled to be published Wednesday in The Lancet and Lancet Oncology.