Water released by a human body is called "sensible" and "insensible" in the medical/scientific world. Sensible is what's released by a body in the form of pee & poo and can be easily measured. Insensible" is moisture released by the body from perspiration and respiration and can't be easily measured. For the average adult in a "normal" temp. and humidity environment, the body releases around 40 ounces per 24 hours (5 cups per day) into the surrounding air from perspiration and respiration.
A more accurate figure of the amount of moisture released into the air by a human (or pet) isn't a question. There's enough moisture released from an average human over 24 hours regardless, that it MUST be removed in cold weather. Then on top of that cooking & showering releases even more moisture into the air.
You have to resist the temptation the seal up every crack and opening to retain heat. The moisture has to be removed. Failure to do so can result in mold, rot & delamination. For more than the odd cold weather weekend outing, a dehumidifier is the best solution as mentioned numerous times. Note also that the warmer air is, the more moisture it will hold so don't think cranking up the thermostat will help. A hygrometer would be a help so you can keep tabs on the RH and they don't cost much.
For occasional weekend trips, running a roof fan and cracking open a a couple of windows can work. We just spent the weekend camping and it was raining hard part of the time. We have one of our two Maxxair fans running non-stop on low and the humidity was hovering around 50% which is fine (2 adults + dog) and no signs of condendsation.
I read of one case where a person wintering in the Seattle area that had water raining down on him from his ceiling. Simply due to a failure to remove moisture from the inside air.
