This is a question that I get asked quite often, and I want to address it and answer it the best I can for you.
I believe that we are capable of performing and doing multiple hours of cardio daily with amazing health and wellness benefits. But let me clarify what I mean by "cardio". Walking around town, a job that requires a ton of walking (nursing, college student, doctor, etc) or even a job that requires a lot of heavy lifting (construction/manual labor jobs) and moving is going to be considered "cardio". Our bodies are designed to be able to perform hours upon hours of this daily and I would actually recommend it. Its healthy to keep your body moving and active.
You have to remember where we came from. Way, way, WAY back we had to hunt and gather our food to survive. That required hours and miles of traveling, hunting, fishing, sprinting, walking daily, and very little food to go along with it. We survived off what we could gather and were active probably 80% of the day. So our bodies are designed to support that sort of lifestyle. Now we have come a long way since then and our bodies have adapted to this new, and I hate to say it but, lazier lifestyle, but as humans we were made to MOVE and EXERCISE.
Daily activity is cardio and I would recommend hours of that. Stay active and walk anywhere you can. When it comes to cardio in the sense of running on a treadmill or being on an elliptical machine for hours then its a slightly different story. I still think an hour to 2 hours isn't going overboard and here's why.
If you have an extremely sedentary lifestyle and the most activity you get is walking to your car, to your office, back to your car, and then home to sit and finish the evening, then getting on a treadmill and doing 1-2 hours of cardio is going to be the best thing for you. I would highly recommend it actually! Along with weight training to ensure your muscles and metabolism won't deteriorate, but thats getting sidetracked and I'll save it for another blog lol. In that circumstance 2 hours of cardio is good. On the other end of that spectrum, if you have a highly active job where you are on your feet all day, get home and then go to the gym and weight lift, and then get on a treadmill for 2 hours of cardio, then I believe it can move into the unhealthy and excessive category.
The intensity of your cardio sessions is also going to play a factor in all of this, and what would be considered too much. Walking is easy on the body. You can walk for hours, and miles, daily with amazing health benefits and nearly no serious damage. Now running, sprinting, and anything high-intensity is going to take a bigger toll on your body. The body needs more time to recover from high-intensity activities and I would not recommend doing those every day, for 1-2 hours. In my opinion that becomes excessive and detrimental to your health.
In conclusion, there is not a specific number that I would consider to be too much cardio for a person. Its all going to be based on your lifestyle, your current health and wellness habits, and the intensity of the cardio in question. Generally speaking, walk for hours a day, in any way you can, and you'll have great benefits from that. But do not do hours of high-intensity cardio every day. I would limit those activities to maybe 1-3 hours a week and divide them up into 20-40 minute sessions, spread out over your week. This will allow your body to properly recover before the next intense session.
I hope this helped out! Thank you so much for reading my blog. Please let me know if you have any other questions that you would like me to answer. Love you!