Low average life span had a lot more to do with high infant mortality rate. It wasn't that most people were dead by 40, just that a lot more were dead by 5. If you made it through adolescence gray hair was totally within reach.
> Analysis of the mid-Victorian period in the U.K. reveals that life expectancy at age 5 was as good or better than exists today, and the incidence of degenerative disease was 10% of ours. Their levels of physical activity and hence calorific intakes were approximately twice ours. They had relatively little access to alcohol and tobacco; and due to their correspondingly high intake of fruits, whole grains, oily fish and vegetables, they consumed levels of micro- and phytonutrients at approximately ten times the levels considered normal today.
That infant mortality was sky-high prior to the 20th century is pretty well known - I can't think of a good, detailed source for that off the top of my head. But what I can tell you, on the subject of longevity in general, is to do the following:
- Look back through the genealogical record, for you personally. "People old enough to have kids" is a good sort-of proxy for life expectancy minus infant mortality. I personally found that my ancestors regularly lived into their 70s and 80s. Very few of my ancestors died younger than 70, going back to the 1600s.
- Another good example is to look at history. Pick up Livy, for example, or someone along those lines, and see how often someone dies of non-violent causes before they've entered old age. It's pretty uncommon. When it did happen, it was usually because of a horrific plague that killed people left and right.
Basically, historically, people generally (we're talking about a huge expanse of time and different cultures here) lived pretty healthy lives. They were much more active than we were, ate fewer processed foods, and often ate very healthy foods. People didn't smoke and didn't eat much sugar. There also wasn't a lot of industry spewing carcinogens and endocrine distributors everywhere. If you lived in a peaceful area and time, in relatively sanitary condition, your odds were very good that you'd live long into old age. Even if you lived in a nasty city (and I'd call Victorian England pretty nasty) your odds weren't bad. Where things fell apart was in war and plague. And as discussed in the paper above, when people did die in old age, they tended to pretty quickly of infection-related causes.
Life expectancy has probably risen and fallen over time, depending on different historical and cultural factors. The popular model of "it's just been getting better and better over time" is not at all correct - it's no coincidence most charts begin in ~1900. The Victorian England paper is a good basis for reflection because it's clear that the medical technology of that time was not dramatically different than that available a few hundred years or even two thousand years earlier, and neither was their diet or lifestyle extraordinary, even if it was good.