An estimated 750,000 elderly people are being forced to choose between paying for food and heating, a charity has warned.
A survey of 1,000 people aged 65 and over for Independent Age found almost half (43%) have gone to bed early to stay warm at least once, with an estimated 890,000 doing this often or every day.
Some 36% said they do not heat their home adequately in winter because of worries about paying fuel bills.
Meanwhile, 6% say they do not eat a hot meal every day in winter (around 673,000 people in the UK), with 6% heating one room or none at all (707,000).
Around one in seven (13%) have gone to a library, shopping centre or used public transport just to stay warm in winter.
Janet Morrison, chief executive of the charity, said: "It is saddening that so many pensioners are faced with the choice of heating or eating during the coldest months of the year.
"While much more needs to be done to ensure that older people get the support they need in winter, there are also many practical actions that can be taken.
"These include wearing several thin layers of clothing, having more milk and dairy to help boost the immune system and drawing the curtains before it gets dark to keep the heat in."
Two-thirds (66%) of those polled said they felt more isolated in winter and go out less often than in the summer months.
Meanwhile, 46% stay indoors because they do not like the cold, and 40% admit they avoid going out because they are worried about tripping or falling.
According to Independent Age, a third of pensioner households have less than £300 a week to live on.
It said 1.6 million elderly people live in poverty, with 900,000 of those living in severe poverty.
The charity has launched a free Winter Wise leaflet for older people, their families and carers.
A separate study from Saga of 10,000 over-50s found 60% wear extra clothing to save money or only put the heating on at certain times of the day.
One in 10 said they go to bed earlier and get up later to save on heating costs, while one in 10 only put their heating on as a last resort.
A spokesman from the Department for Work and Pensions said: "This Government continues to protect pensioners with its commitment to a minimum annual state pension increase of 2.5%, as well as the maintenance of universal benefits including winter fuel payments and targeted help for the poorest through cold weather payments and the Warm Home Discount Scheme."