Britain's lifts are no longer big enough to fit oversized people as waistlines across the country balloon.
Engineering experts warned lift capacity signs for the maximum number of passengers are "out of date".
In the mid 1970s in the UK, the average weight of a man was 75kg, while the average weight of a woman was 65kg, experts said.
Now this is around 86kg for men and 73kg for women, they added.
Lift manufacturers are required to display maximum number of passengers the lift can accommodate.
Experts wanted to examine whether lift design has kept in line with trends in weight over time.
Between 2000 and 2024, Professor Nick Finer, President of the International Prader Willi Syndrome Organisation, gathered data from 112 lifts across the UK, France, Germany, Spain, Italy, Austria and Finland.
The lifts had been manufactured by 21 companies between 1970 and 2024.
Waistlines are ballooning across Britain
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Average weight allowance per person, which is calculated by dividing maximum weight allowance by maximum number of passengers, for the year of manufacture was compared to average adult weight for that year obtained from the UK National Health Survey.
Professor Nick Finer found that between 1972 and 2002, the maximum weight in lifts was correlated to increasing population weight.
However, after 2002 there was no significant increase in the assumed average weight of lift users.
He added that manufacturers assumed average weight remained at 75kg, while the average population weight was 79kg.
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Lift capacity signs are 'out of date'
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Prof Finer told the European Congress on Obesity in Istanbul, Turkey: "The failure of lift manufacturers to adapt to rising levels of obesity and body size means that lift capacities are overestimated meaning that journey times are likely to be increased and that safety could be compromised.
"What’s more, suggesting more people can fit in a lift than is comfortable is stigmatising people living with obesity."
In an abstract presented to the conference, he said "overall manufacturers were not adjusting the capacity of lifts to reflect secular increases in population average weights".
According to the NHS, 30 per cent of adults in England were obese in 2024, and 66 per cent were either overweight or obese.
The data suggests 66 per cent of adults were either overweight or obese
| GETTYNew NHS England data has suggested more than 6,000 severely obese children in England have sought help from specialist weight management clinics in just three years, including more than 400 under the age of four.
Some of the children referred to the Complications from Excess Weight (CEW) for children initiative weighed 123kg at the time of referral.
Some had a body mass index score (BMI) of 42, indicating that they were very severely obese.
Around 17 per cent of these youngsters had developed high blood pressure and six per cent had type 2 diabetes while many also had liver disease and obstructive sleep apnoea.
Childhood obesity levels in Britain are rising
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NHS England’s national Clinical Director for Children and Young People Professor Simon Kenny said: "These specialist clinics support children to lose weight safely and build healthier long-term habits through tailored care from expert NHS teams.
"In some cases, these clinics are helping children who could otherwise face a life cut tragically short, dying decades too soon, to look ahead to a full and healthy life.
"Childhood obesity remains one of the biggest public health challenges facing the country, and the NHS is committed to stepping in early to help prevent serious long-term health complications."