By contrast some now abandoned medical treatments like flecamide for heart patients ran into the frightening thousands per million treated. It is worth remembering that all drugs have side effects. A tragic example is the drug thalidomide which was taken by pregnant mothers to help them sleep and which was tested without ill effects on rodents, but caused limb deformities in human babies at very low doses. Some chemicals in the environment have known effects on health and the risk associated with this can be assessed. The most reliable way to find out what, if any, are the effects of an environmental agent if they are not already obvious is to record effects on representative sections of the population.
Nuclear radiation is known to cause cancer, particularly leukemia.
It is possible to calculate the effect of this radiation to which we are all naturally exposed in the United Kingdom, and it turns out to be responsible for about four percent of all deaths due to cancer. Sunlight's effect is more striking and is responsible for the majority of skin cancers including melanoma. Smoking is about five hundred times more dangerous than pregnancy complications but the average loss of life expectancy is fifty years for women who die in childbirth but only fifteen years for men who die from smoking-related diseases. For men involved in traffic accidents the risk is twenty times less than smoking but the loss of life expectancy is thirty years. As far as sports are concerned rock climbing is over one hundred times more dangerous than skiing.