One of the documents of use to a family historian is a death certificate. It is a primary document for the death itself and burial location, but is also a secondary document for other events such as the decedent's birth, names of decedent's parents, and locations of these births. If we're lucky, it also lists an actual cause of death, which can be a history lesson in itself. Some of the causes of death are now obsolete terms and, in most cases, nowadays the cause is more detailed than "old age".
The cause of death can also perhaps answer questions about the lifestyle of the decedent. Some health issues are caused by not only a lack of a nutrient, but in some cases by an overabundance of a nutrient. In my ancestry, one of the great-grandfathers died of pellagra. I had never heard of this "disease" before I saw it on his death certificate, so I did a search. What I found is that pellagra is a niacin deficiency common in corn-based diets that can be fought with adequate fruit and vegetable intake. The native Americans used lime which made the niacin more accessible to the body therefore reducing the likelihood of developing pellagra.
I also know that alcoholism is a common occurrence in my Gunter ancestry and alcohol is generally corn-based. Knowing our family history and the cause of death being pellagra, it leads me to wonder a couple of things. Did Big Papa basically die of alcoholism or could it have been the other common trait in my ancestry, which was poverty? Lack of access to healthy foods obviously leads to vitamin deficiencies. He was a textile worker and they generally earn next to nothing. Another grandpa who was a mill worker during this time frame made less than $600 a year. Big Papa had a wife and six children to feed, so I can't imagine that $600 went very far at all.
Often, answers to questions bring even more questions. Be sure to closely investigate all of the possible sources of information during your genealogy adventure. Sometimes what appears as one thing may really be telling you something entirely different from what it appears.
Wikipedia contributors, "Pellagra," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Pellagra&oldid=543694616 (accessed April 4, 2013).