They are the leading causes of illness and death in the United States today: heart disease, cancer, stroke, chronic obstructive pulmonary disease, diabetes and Alzheimer's disease, in that order. And they have a lot in common.
They are expensive - together, they account for 25 percent of the nation's annual health care expenditures, said Jonathan Skinner, a health economist at Dartmouth College.
They come in clusters - accumulations of plaque in arteries lead to heart attacks but also can lead to strokes and predispose to Alzheimer's disease. Diabetes can lead to heart disease, stroke and even cancer. Smoking can lead to chronic obstructive pulmonary disease as well as cancer and heart disease, which in turn predisposes to Alzheimer's.
And the outlook for them is improving - people are getting the diseases later in life, and death rates are falling.
Yet, in many instances, patients are undertreated or treated inappropriately. In some cases, science has not offered answers, but in others, the medical system has been unable to turn proven remedies into everyday care.