Chronic cardio or other long session exercise is bad for the body, recent science is coming firmly down on the side of short sharp exercise instead like Tabata sprints etc.
http://www.ncbi.nlm.nih.gov/pubmed/19633305
Atherosclerosis =-=-=-=-=-=-=-= http://www.ncbi.nlm.nih.gov/pubmed/21200345
http://www.healio.com/cardiology/chd-prevention/news/online/...
http://www.ncbi.nlm.nih.gov/pubmed/18426850
Oxidative Stress =-=-=-=-=-=-=-=- http://www.ncbi.nlm.nih.gov/pubmed/16941810