Based on scientific research performed over the last few decades it has become evident that exercise is pretty effective medicine in many clinical conditions. This fact is being promoted for instance by the leading Association in the field, American College of Sport Medicine.
Even if exercise cures and helps to manage many diseases, there are some clinical conditions such as diabetes that are quite challenging to treat successfully even with combined drug, physical activity and dietary solutions. In regards to diabetes, it has been well shown that exercise can very effectively reduce the incidence of new diabetes cases. Similar analogue seems to be the case in preventing cardiac and vascular diseases, altogether meaning that exercise is very good strategy in primary prevention, that is preventing diseases to occur at first place.
There are numerous ways that exercise maintains and improves fitness and health, but one of the most interesting one is exercise as anti-aging agent. This has been shown fairly recently by professor Mark Tarnopolsky and his team, who performed various experiments to show also mechanistically how exercise modifies the skin of old persons, to look almost identical to 20-year old skin! A bit later came also an interesting study showing how exercise promotes enzyme called telomerase to keep cells to stay young and fit. Furthermore, to support the importance of exercise boosting telomerase function, it was recently reported that sitting promotes cellular aging, but this can be eliminated by performing 30 min of physical activity per day.
Last but not least, a study published in the Heart reported last year that it is largely your fitness that determines your biological age. According to the study there are differences of up to three decades in persons’ biological age depending on their fitness. It was illustrated in the study that for instance in case of a 45-year old woman, her biological age can be 27 years of age if she is fairly fit, or 60 years of age if she is not that fit. And fitness here does not mean any athletic aerobic fitness (that is some 65-75 ml/kg/min, maximal oxygen consumption, VO2max), but a fitness of approximately 45 ml/kg/min for VO2max. Interestingly, this is a bit higher fitness that has been shown by Norwegian researchers to eliminate the health hazards of daily sitting. Same ideas apply to men too, even if in these examples women were used as an example.
Finally, it is not that exercise would necessarily prolong your life that much, but it likely keeps you fit also later in your life to do even physically demanding things if you just want. This is nicely illustrated in a figure in this article that is certainly worth of reading for further information on the topic.