The decline from the early 80s is down to a number of things I think. Firstly heath awareness and diet. Levels of smoking also began to fall dramatically as did the number of men in heavy dirty industries, coal mining, steel works, working with asbestos etc. Health and safety got into full swing, car accidents became much more survivable. Medical advancements came on in leaps and bounds such as cancer detection and treatment. Golden years of heath progress.