By Michelle Roberts
Health reporter, BBC News
More than 23,000 elderly people died as a result of being too cold last winter in England and Wales.
Wearing the right clothes in winter could save lives
The year before the toll was 29,000, which is nearly 10 people aged 65 or older every hour.
Yet temperatures only dropped to 4C on average.
Latest figures for Scotland show the nation's winter death toll was the lowest on record. Deaths fell by nearly 1,000, but still totalled 1,790.
Meanwhile, the coldest city in the world, Yakutsk in east Siberia, has no excess winter deaths, even though temperatures there can drop to minus 49C.
So why and how are so many people perishing in the UK from the cold?
Professor Bill Keatinge, an expert from Queen Mary University of London, has studied the issue extensively.
He said: "On the whole, the countries that have the mildest winters tend to have a higher mortality than countries with very cold winters.
"This is because the deaths in winter are not due to massive cold, with people being overwhelmed in their own houses and dying of extreme cold.
"It's down to quite minor degrees of cold that people were getting every day."
Prolonged exposure not big chill
He said very few of the deaths were caused by true hypothermia, where the core body temperature drops significantly.
"Most of them are due to strokes and heart attacks.
"This is because the blood becomes more liable to clot in people who are exposed to the cold."
TEMPERATURE EFFECTS ON COMFORT AND HEALTH
24C - top range of comfort
21C - recommended living room temperature
Less than 20C - death risk begins
18C - recommended bedroom temperature
16C - resistance to respiratory diseases weakened
12C - more than two hours at this temperature raises blood pressure and increases heart attack and stroke risk
5C - Significant risk of hypothermia
Source: West Midlands Public Health Observatory
When exposed to cold, the body contracts down the blood vessels in the skin to stop blood flowing to the skin and to prevent heat loss.
This means more of the blood circulates to central parts of the body, which overloads the heart and lungs with blood.
The body gets rid of fluid to reduce this load by excreting salt and water, but the net result is the blood becomes more concentrated and liable to clot.
The next biggest cold-related killer is respiratory infections such as flu.
But Professor Keatinge added: "Flu epidemics have been declining for over 30 years. The last really big one was in 1976."
He said this was mainly down to recent flu viruses being less virulent rather than medical interventions such as annual flu jabs for the elderly.
"The fact that we now keep much warmer in winter and we are aware of the problem means that all the various causes of cold-related illness and death have declined," he said.
But he said people in the UK and places like Portugal, which also has a high rate of excess winter deaths, were still pretty poor at keeping warm in winter.
"People in the north of Finland take great precautions against cold. They keep their houses warmer in winter than we do, and they are much better equipped for outdoor cold.
"They have much better outdoor clothing. They take it very seriously."
Although we are getting better at keeping our houses warm, Professor Keatinge said people in the UK often dress unsuitably for cold weather.
"There is no problem about being out in winter if you are suitably clothed and you are exercising and you stay warm.
"But if you wait for a bus and you assume a bus is going to come in five minutes and it doesn't come for 45 minutes, and you are at a windy stop with no shelter and without adequate clothing you can get very cold indeed.
"Public transport is a menace from this point of view. It doesn't have to be, but we tend not to have very well heated waiting rooms for trains and bus shelters that are not wind-proofed. That is probably a substantial source of problems," he said.
Studies show elderly people, and particularly those on low incomes, are at the greatest risk. There are a number of reasons why.
Those that succumb are not necessarily sick already, but older people's blood vessels tend to have rougher linings than those of younger people, which makes them even more susceptible to clotting.
Even mild winters claim lives
Those on small pensions might struggle to keep their houses warmer and might have to rely on public transport or walk rather than use a car, for example.
Professor Keatinge also warned that global warming could make the situation worse rather than better.
"Global warming is making our winters milder and that could be dangerous. If people stop worrying about cold they get more careless about heating their homes and wearing warm clothing."
'Don't be complacent'
Mr Patrick Sachon from the Met Office said winter deaths go up by about 1.4% for one degree drop in temperature below 18C.
"So it doesn't have to be that cold to start to increase mortality," he said.
"Our winters are much milder than in other countries. It rarely gets below minus five. Most winter days, the temperature usually gets above freezing and when it's mild, it can be 13C.
TIPS ON STAYING WARM AND SAFE
If you take medicine for a health condition, make sure you have enough of it and keep it at hand
Wrap up warm
Keep your bedroom at 18C
Keep your living room at 21C
"But even when it is relatively mild, if there is a strong wind that can make you cold and people are not prepared for that when they are out and about.
"In this country, people don't think about what getting cold will do to them because it doesn't kill them immediately.
"We don't have well insulated houses and we have a culture that believes having a window open to let in lots of fresh air is good for us, even though it is not.
"What you should actually be doing is keeping your living room at 21C and your bedroom at 18C, which is quite warm by most people's standards."
He said this winter was likely to be another mild one in the UK, but he warned this was no reason for people to be complacent.
"We could still get a cold snap. People need to realise that cold can kill and they need to keep warm," he warned.