Firstly Heart Disease
, Heart disease has two seperate primary factors Lifestyle and genetics. Livestyle factors, such as obesity, too much colestoral and lack of exercise, can be altered by a person's actions however Genetic factors, such as the Aortic Stignosis that i myself suffered from in my youth, can not be.
Cancer, rather than a single disease is a number of closely related problems and so to condense it down to a single cause is rather foolish. While some cancers such as Skin, Lung and Throat cancers are known to be brought on by enviromental factors, sunbathing
respectively, However these by themselves are not entire causes, since genetic diseases such as Lupus
can increase people's chances of getting cancer.
is primarily caused by a clot in the brain. As such while this can be encouraged by certain enviromental factors it comes down to a number of medical factors.
So the awnser is that in some cases they may be preventable or at least have their impact reduced by individual choice but there is no way that we can lay the blame for these conditions at the feet of individuals.