It also depends greatly on how well your structure is insulated and where (or whether) vapour barriers exist.
Vapour condenses against cold surfaces. This is why in winter poorly-glazed (e.g., single-glazed) windows "steam" up (really: condense), or frost over. Similarly water will condense against exterior walls, and may lead to degraded sheetrock (newer construction) or plaster (in older buildings), or rot. Where walls are insulated, a vapour barrier _before_ the insulation can lead to condensation inside the wall, again, against the exterior (cold) surface. The result is that even if the interior is humidified, moisture is "sucked out" by the exterior cold. (More accurately: vapour condenses against cold surfaces.)
In summer, the problem is reversed, with warm humid exterior air condensing on surfaces cooled by interior air conditioning --- the outside of windows, or again, inside walls. Interiors can see higher relative humidity than the outside, and dehumidifiers may be needed.
