from the dozens of questions I have asked I have gathered that yes it is true, but those living in colder climates say as long as you don't keep them overly warm during winter they will be fine.
I have a heat lamp in my coop, winter temps here where I live drop to -30's very often, Everyone I have talked to has told me to be sure the coop is draft free, draft free, draft fee...with plenty of ventilation. some insulate their coops some don't, some provide light, some don't. Its all on what you prefer.
I put my heat lamp facing the roost where they huddle together. its already down to -12F here. I think more people will give you better ideas on what you should do. Heat lamps are a cause for coop fires, so if you use it be sure to double, triple clamp it in case it comes unhooked in or area or other. BYC members with more experience will guide you better than I can.
Good luck
Ema