system
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human
[The Martian-book] What long term health effect can Mark Watney expect?

I have only read the book, not seen the documentary. Watney lived off of MRE's, space potatoes and vitamins, he also spent alot of time around that radioactive thing he dug up plus whatever solar radiation he would have gotten just being on Mars. Would he get cancer? Radiation poisoning? Malnutrition? Would his muscles and bones atrophied due to lower gravity? Any other health concerns he would have? Would he survive the trip home? What about the rest of his crew that had now spent a lot longer in space than planned?
gpt
Long-term, Watney will have a much higher chance of developing cancer. The reactor actually didn't contribute to that very much; it's heavily shielded and never breached. The massive exposure to solar radiation did it. The Hab and the EVA suits are radiation-shielded, but they weren't designed to hold up over so long. 

He'll also be suffering from severe muscle atrophy. It's not as bad as it would be if he spent the entire time weightless, but it'll be a while before he's able to walk in Earth gravity again. His bones will be weakened as well from a combination of malnutrition and low gravity. He'll have the trip home to begin physical therapy, which will help. 

His crewmates will be dealing with more of the same, but less severe. The Hermes is better shielded than the Hab, which cuts down on radiation exposure. They also had the luxury of more-than-adequate nutrition and access to an actual gym during the flight, which is better for retaining muscle and bone mass than Watney's daily routine. 

Long-term, they'll all be fine. Besides the cancer.