The strokes, heart attacks and chest illnesses that kill the elderly are far more common in cold weather. The relationship between death and temperature is alarmingly direct - in a mild winter, such as the last, there will be only 20,000 "extra" deaths, while in a severe one the figure will reach 40,000.
Tens of thousands of our pensioners have their lives shortened simply because they cannot keep themselves warm enough to stay healthy. It is a peculiarly British failing. Scandinavian countries, which have winters far more severe than ours, have half the number of excess winter deaths.
Violet Newitt, an 87-year-old widow, is trying her hardest not to become a winter death statistic. Sitting in her north-west London council house in furry, zip-up boots and a double layer of woollies, she sets out her battle against the cold.
Hot packet soups, charity shop woollens, and as much exercise as arthritis and a bad back will allow, are key elements in her strategy. As she is asthmatic, consistent temperature is vital (moving from warm to cold could bring on an attack) so her home is centrally heated. The boiler burns most of the day because she is nearly always at home, but she keeps the thermostat as low as possible.
Brent Council fitted double glazing recently, but the loft insulation needs renewal - it has not been touched for at least a quarter of a century. Mrs Newitt needs a smaller house with better insulation. She is on the waiting list for a council bungalow, but has no idea when one will become available.
Mrs Newitt spends more than a tenth of the pounds 450 a month she receives from her old age pension and benefits on gas and electricity. But she is among the luckier ones. More than a million households, mainly pensioners, need to spend at least 30 per cent of their income to keep their homes warm. Most cannot afford to, and go cold instead.
Brenda Boardman, an expert on energy efficiency at Oxford University, says that Britain's poor winter mortality figures are largely a result of bad housing: "The poorest pensioners are often found in the homes that are hardest to keep warm."
So what can be done? Age Concern, one of the charities to benefit from The Independent's Christmas Appeal, is backing a nationwide campaign to help advise on and implement energy-saving home improvements.
Last year it launched a pilot scheme, "Safe and Warm", in which volunteers and paid workers in 10 towns met pensioners, gave them advice on fuel saving and helped them apply for grants. So far, 15,000 people have been reached.
One of them is 65-year-old Jean Evans, who has just retired from her job as a sheltered housing warden. She moved into a Housing Association flat in Portsmouth last summer. It had two gas fires and no central heating. That June was exceptionally cold, and she used a portable electric heater to keep her bedroom warm because the gas fire was broken. She was horrified when her first electricity bill came to over pounds 100 - and she is still paying it off.
An Age Concern "Safe and Warm" team draught-proofed her front door and hung a thick, insulating curtain over it. The gas fire has been repaired and now that security locks have been fitted to the house she feels feels safer too.
The Independent Christmas Appeal: freephone 0800 00 99 66.