Heart disease, type 2 diabetes, and I believe Alzheimer's as well, seem to all be the result of the body's plumbing being clogged up by fat and cholesterol deposits. Exercise, a diet low in artificial fructose, saturated fat, and trans fats, but high fiber, seems to be effective at reducing your risks.
Diabetes II is the result of insulin not being effective because of inter-cellar build ups; heart disease is when your heart cannot get blood to function because of build up in the vessels that supply it.
Would it be fair to categorize these health issues as different manifestations of the same disease, similarly to how we call many different kinds of cancer "cancer"?
Evidence that Alzheimer's may be a form of diabetes: http://ncbi.nlm.nih.gov/pmc/articles/PMC2769828