Exercise is undeniably good for long term health, far better than any medical technology presently available - but why? Here is an overview of some of what is now known: "Physical activity has long been known to bestow such benefits as helping to maintain a healthy weight and reduce stress, not to mention tightening those abs. Now, a growing body of research is showing that regular exercise - as simple as a brisk 30- to 45-minute walk five times a week - can boost the body's immune system, increasing the circulation of natural killer cells that fight off viruses and bacteria. ... No pill or nutritional supplement has the power of near-daily moderate activity in lowering the number of sick days people take ... Regular exercise has been shown to combat the ongoing damage done to cells, tissues and organs that underlies many chronic conditions. Indeed, studies have found exercise can lower blood pressure, reduce bad cholesterol, and cut the incidence of Type 2 diabetes. ... exercise-induced changes in the body's immune system may protect against some forms of cancer. ... Researchers are also investigating whether exercise can influence aging in the body. In particular, they are looking at whether exercise lengthens telomeres, the strands of DNA at the tips of chromosomes."