Exercise!
Exercise is more powerful for the healthy than any presently available medical technology when it comes to maintaining health and establishing a good life expectancy: "Regular exercise can reduce around two dozen physical and mental health conditions and slow down how quickly the body ages, according to a research review summarising the key findings of 40 papers published between 2006 and 2010. .... Health conditions covered by the review include: cancer, heart disease, dementia, stroke, type 2 diabetes, depression, obesity and high blood pressure. ... The literature reviewed shows that how long people live and how healthy they are depends on a complex mix of factors, including their lifestyle, where they live and even luck. Individuals have an element of control over some of these factors, including obesity, diet, smoking and physical activity. ... Ideally, to gain maximum health benefits people should exercise, not smoke, eat a healthy diet and have a body mass index of less than 25. The more of these healthy traits an individual has, the less likely they are to develop a range of chronic disorders. Even if people can't give up smoking and maintain a healthy weight, they can still gain health benefits from increasing the amount of regular exercise they take. Physical inactivity results in widespread pathophysiological changes to our bodies. It appears that our bodies have evolved to function optimally on a certain level of physically activity that many of us simply do not achieve in our modern, sedentary lifestyles. ... What is clear from the research is that men and women of all ages should be encouraged to be more physically active for the sake of their long-term health."
Link: http://www.sciencedaily.com/releases/2010/11/101115074040.htm