"Your Hardcore Run May Be as Dangerous as Sitting Around Doing Nothing"
http://www.bloomberg.com/news/articles/2015-02-02/light-joggers-can-outlast-the-ironmen-over-long-term
"The researchers found those who jogged one to 2.4 hours a week at a slow or average pace with no more than three running days in a week had the best survival rates. Anything longer than that left runners with death rates closer to those who didn’t run at all, the authors said."
Doctor Ken Cooper who has done more research on aerobic cardio exercise than just about anyone put it simply. He said in effect if you are running more than 3 miles a day you are doing it to become a better athlete and not necessarily to increase your health.
Cardio has prevented more heart attacks than it has caused. The first thing Doctors have you do in cardiac rehab is cardio exercise.
Cardio can do the following things for your health.
Lower your resting heart rate that illustrates your heart muscle is stronger.
Low blood fats as in triglycerides.
Lower visceral fat that causes metabolic problems like diabetes.
Lower high blood sugar
In many it can lower blood pressure
It can change the ratios of HDL and LDL for the better.
Lower subcutaneous fat.
Running can increase bone density.
Many report lower incidence of depression after starting a cardio routine
Can lower cholesterol from less visceral fat that can lead to metabolic problems causing a liver to produce more cholesterol.
Increases capillaries alternate pathways in the blood supplies to the heart that can spell the difference between life and death when a blockage occurs.
Cardio can lower inflammation which many doctors believe the C reactive protein test can be a predictor of risk for heart problems.
That's all I can think of for now. Is cardio activities like running a cure all? Obviously no, but it can lower the risk factors and in life putting the odds in your favor is always a wise move.