Part of the reason for the increase in degenerative diseases is that we're living a lot longer than we used too.
(detailed tables #10)
22,960 75-year-olds were alive in 1900, compared with 65,717 in 2003.
Since we live longer than we used to, any diseases that are more common in the elderly are more common. Some of these are heart disease and cancer, dementia, alzheimers, etc. So it's really not all that surprising that as we get more 75-year-olds, we see a lot more degenerative conditions. Some of this may be food related, but I think there's also the cruel twist of evolution. Evolution cares whether you have and successfully raise children. Once you've reproduced and your children are grown, evolution doesn't care about what happens, so your body isn't designed to last much past that. Sure we can slow down the aging using tricks and modern medicine, but eventually you reach the upper limit of how long a human being can live.