A study done at the University of Navarra in Spain published an article in the Journal of the American Heart Association in June of 2014 that followed more than 13,000 healthy people with an average age of 37 for more than 8 years. They assessed 3 different types of sedentary behavior to see if they had an effect on premature mortality. What they discovered is that watching TV for more than 3 hours a day, compared to 1 hour a day, doubled the risk for premature death. There were 97 deaths, 19 from cardiovascular causes, 46 from cancer, and 32 from miscellaneous causes.
Previous studies have found that excessive TV watching can increase blood pressure and weight in children. It is a good idea to limit TV watching for both kids and adults!