Average life expectancy in the UK is expected to increase from 80.8 years to 83.3 years by 2040, an analysis suggests.
This would put the UK in 23rd place out of the 195 nations analysed, up from 26th place today.
Spain tops the charts, with people being born in 2040 expected to live until they are 85.8 years old.
Lesotho, within South Africa, will be worst off with its average life expectancy likely to be just 57.3 years.
The US will drop from 43rd to 64th place with an increase of just one year, according to forecasts by researchers from the University of Washington’s Institute for Health Metrics and Evaluation.
The research, reported in the Daily Mail, said although people in every country in the world are likely to live longer in 2040 than they do now, there will be a rise in the number of people dying from non-contagious diseases like cancer and lung and kidney disease.
How quickly countries’ life expectancies rise will depend on how well governments deal with these growing health threats.
“Inequalities will continue to be large,” said researcher Dr Christopher Murray. “In a substantial number of countries, too many people will continue earning relatively low incomes, remain poorly educated, and die prematurely. But nations could make faster progress by helping people tackle the major risks, especially smoking and poor diet.”
Beneath Spain in the top 10 will be Japan, with a 2040 life expectancy of 85.7 years, Singapore (85.4), Switzerland (85.2), Portugal and Italy (84.5), Israel (84.4), France (84.3), and Luxembourg and Australia (84.1).
To make the predictions, the scientists looked at the impact of 79 health factors including smoking, body mass index (BMI) and lack of clean water and sanitation on causes of death around the world.
In 2016 – the last time the study was carried out – four of the top 10 causes of premature death were non-communicable diseases and injuries.
The new forecast shows that by 2040 this figure increases to eight, with heart disease, stroke, chronic lung disease, chronic kidney disease, Alzheimer’s disease, diabetes, lung cancer and road accident injuries are all in the top 10 causes of premature death in 2040.
The study was published in medical journal The Lancet.