In accordance with this functional decline, age is the major risk factor for the development of chronic medical conditions. In the United States, nearly 50% of individuals over the age of 65 develop cardiovascular disease; 35% develop arthropathies; 15% develop type 2 diabetes; and 10% develop pulmonary disease. Some of these conditions are particularly debilitating and extract a significant social and economic toll. Stroke and dementia, the most common causes of long-term institutionalization of individuals over 65, cost the US health-care system alone $21 billion per year — a cost projected to rise by 14%, to $24 billion, in 2010 (ref. 6). Advancing age is also the major risk factor for the development of cancer. Specifically, between ages 40 and 80, there is a rapid increase in cancer incidence that produces an overall lifetime cancer risk of nearly one in two individuals in industrialized nations7. Thus, diseases of the aged collectively constitute the major causes of human suffering and consume the bulk of our health-care resources. From this perspective, the need to understand the nature of ageing and how its consequences can be managed, and possibly reversed, has never been greater.
