The cancer picture is not as clear in non-smokers, but Peto said he was surprised that being overweight had such an impact. Scientists aren't sure of the mechanism through which excessive weight increases the risk of the disease or if it can be reduced if people lose weight. There is now a consensus that cancer is commoner in those who are overweight. Infections and a weakened immune system are other known risk factors for cancer, along with excessive alcohol, sunlight and pollution. Doctors also suspect childhood leukaemia is triggered by an infection, but scientists have not pinpointed the cause.
Viruses are particularly important in the developing world.
Genetic susceptibility is also a risk factor in many types of cancer, but Peto added that most of the genes involved remain to be discovered. Reuters shall not be liable for any errors or delays in the content, or for any actions taken in reliance thereon. Reuters and the Reuters sphere logo are registered trademarks and trademarks of the Reuters group of companies around the world.