No it's not. I retired at 57, now 66 and happier than heck. Good health and a son that just turned 20 today.
Simple fact, life is better for some than others. I have no clue why.
Personally, I think the answer is Boxers vs Jockey's.
IMO, these types of studies are done in order to discourage people from retiring early in welfare states in order to cut down on the amount of money paid out to the retirees. Back in the 70s, I think it was, there was a study done on similar lines in the US and they were urging people not to draw there SS before they reached full retirement as they might die sooner.