Nearly a quarter (24%) of older people believe they will be forced to choose between heating their home and the food they buy if their energy bills increase substantially.
More than half (54%) of those surveyed said they would have to heat their home less, a survey for Age UK found.
And just over two-fifths (43%) said they would have to cut back, go into debt or simply will not be able to afford to pay their bill, according to the research among over-65s.
Inflation jumped to a near 30-year high of 5.4% in December and the energy price cap is due to rise in the spring, possibly increasing bills by 50%, according to predictions.
One 69-year-old woman told Age UK: “I am currently in bed keeping warm today as it’s so cold and I can’t afford to have my heating on for the whole day.
“I’m reduced to showering on alternate days, which I hate, and I’m eating food that’s microwaveable to avoid heating my oven.”
Age UK warned that many older people are missing out on extra income as well as vital support such as Cold Weather Payments and the Warm Home Discount Scheme because they are not receiving Pension Credit, despite being eligible.
It said many older people on low incomes are unaware that they qualify for Pension Credit, and that a successful claim opens the door to a wide range of other support, including help with energy bills.
As part of its campaign The Cost Of Cold, Age UK is urging any older person on a low or modest income who is struggling with their bills to have a full benefits check.
People can call the charity’s advice line on freephone 0800 169 65 65, contact their local Age UK office, or visit www.ageuk.org.uk.
Caroline Abrahams, charity director at Age UK, said: “Many older people are reliant on the state pension as their main source of income and simply do not have the flex in their finances to cope with such enormous price rises.
“At Age UK, we are being contacted every day by desperate older people in this position, people for whom there are only ‘bad choices’ – ration your energy use, cut back on food or other essentials, or go into debt.”
She added: “Any older person who is finding it difficult to pay their bills, or who is worried about staying warm, can call us today – if we help you to submit a successful claim it could make all the difference.
“There really is no downside to checking you are receiving everything you are entitled to, so please come forward and let us help you make sure.”
A Government spokesperson said: “We know this has been a challenging time for many people, which is why we’re providing support worth around £12 billion this financial year and next to help households across the country with the cost of living.
“Our winter fuel payments are supporting over 11 million pensioners with their energy bills and we are continuing to encourage those eligible for Pension Credit, and the wide range of other benefits it can provide, to make a claim.”