Interesting in this respect is that exercise can have a positive modifying effect. I was wondering, if one of the mechanism involved (apart from modifying your immune response, as quoted in the article), was to eliminate cells that are harboring pathogens in the cell itself, by stressing it - and because they are infected, their resistance might be limited (similar to the mechanism that can eliminate muscle cells with damaged mitochondria).
Tom Lonsdale, the Veterinarian that wrote 'Raw Meaty Bones' about a natural diet for dogs and cats, found that early signs of 'diseases of ageing' in dogs and cats were caused by periodontal infections and diseases. His view is that processed and prepackaged diets were the cause - not only because of the reliance on ingredients that would not ordinarily have been part of the natural diet, but also because the food didn't clean, massage, stretch, stress or exercise the teeth, gums and jaw.
Maybe it's good to go for the tough, sinewy meat from an older animal regularly rather than the younger, tender, easier to chew stuff.