I would have thought the most likely cause of this was social change.On the other hand the life expectancy for a man in England and Wales was 66 in 1948 and it is now 79 so not all bad.
Most of the men in my family died in their early sixties, my dad at 55. They left school at 14, went into manual jobs, engineering ,mining etc, with no H&S rules. Were smoking at 14 and only one room of the house was properly heated. I can remember frost on the inside of the bedroom windows. No antibiotics, no preventative health care. I can just about remember the black buildings that were cleaned in the 70's that were covered in soot.
My maternal granddad died before he retired. He was in the WWI, came home with shell shock and then went back down the pit, where he started work looking after pit ponies when he was 14. The good thing is he raised seven healthy daughters, who lived into their 80's, perhaps because they rarely smoked and worked in the home.