People in the UK will be living an average of three years longer by 2040, according to new research.
Experts believe that it will go up from the current figure of 80.8 years to 83.3 years - with Britain set to have the 23rd highest average lifespan.
But they are easily outranked by the super-healthy Spanish - whose predicted average lifespan of 85.8 years puts them at the top of scale.
Spain is forecast to overtake Japan, ranked first in 2016, with the latter tipped to drop into second place with an average lifespan of 85.7 in 2040.
African countries continue to have the worst rates of premature death.
The research, published in The Lancet medical journal, shows that, on a global scale, average lifespan for both men and women is expected to increase by 4.4 years.
Citizens of the Central African Republic, Lesotho, Somalia and Zimbabwe are still expected to die before the age of 65 by 2040.
Notably the US makes the biggest drop down the league table, falling from 43rd place in 2016 to 64th in 22 years' time.
Average life expectancy in the US, one of the world's richest nations, is forecast to increase by only 1.1 years to 79.8.
Lead author Dr Kyle Foreman, from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington, US, said: "The future of the world's health is not pre-ordained, and there is a wide range of plausible trajectories. But whether we see significant progress or stagnation depends on how well or poorly health systems address key health drivers."
To carry out the study, researchers looked at the impact of 79 independent drivers of health including smoking, high 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 (NCDs) and injuries.
The new forecast shows that by 2040 this figure increases to eight. 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.
IHME director Dr Christopher Murray said: "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."
Lifespan gains around the world are likely to be checked by factors such as high blood pressure, diabetes, obesity, tobacco and alcohol use, and air pollution, according to the study.
The top 10 lifespans by country predicted for 2040 are as follows: Spain, 85.8; Japan, 85.7; Singapore, 85.4; Switzerland, 85.2; Portugal and Italy, both 84.5; Israel, 84.4; France, 84.3; Luxembourg and Australia , both 84.1.