My guess is it isn't cold itself that kills, but the effects of living in a cold, and damp, environment. Take the UK for example, many houses are over 100 year

My guess is it isn't cold itself that kills, but the effects of living in a cold, and damp, environment. Take the UK for example, many houses are over 100 years old, made of brick and little insulation. Even before energy prices went crazy, during the winter you'd be paying hundreds of pounds a month for heating and some parts of the house would barely reach 20c. In most parts of the UK, temperatures below freezing are rare so it's probably +5C or similar outside at that time. And its an island that rains a lot, so combine that with 90% humidity and you have a rather high dew point. Now back to the energy prices. Gas prices in the UK are around 3x what they were before COVID, and electricity prices around 5x - and let's not even start about other living costs. So you do as the media says and try to save money and energy by turning down the thermostat. Maybe you also turn off the radiator in the spare bedroom, and try to be smart by sealing up drafty windows. This means your cold and damp home will be closer to the dew point and is going to be less ventilated (forced air heating or ventilation is not a thing in the UK; you ventilate by opening windows), which will to lead to more mold and fungus, and we have something which causes health issues. The winter in the UK was colder than normal too, with more days below freezing than usual. (I'm from the UK, but live somewhere colder now, but as the humidity is so low during winter and houses are insulated properly, mold is not a thing here)