Working conditions must be improved for older people if governments and companies are to persuade them to continue contributing to economic growth into their old age, according to Swedish and British scientists.

Researchers analyzed almost 15,000 employees in France and found that they felt increasingly less well in the years leading up to retirement, but dramatically better after they stopped work -- suggesting they saw work as harmful to their health.

Our findings should cause concern for policy makers attempting to convince workers to stay longer in the workforce, said Hugo Westerlund of Stockholm University's stress research institute, who conducted the study with colleagues from University College London.

The study, which took annual surveys of the workers' self-rated health, found that between the year before retirement and the year after, the risk of workers saying they were not well fell from 19 to 14 percent -- a drop the researchers said corresponded to a gain in health of eight to 10 years.

Put another way, in terms of the risk of suboptimal health, people suddenly got eight to 10 years younger when they retired, they wrote. And the retirees continued to feel better throughout the seven years the study followed them.

Populations are aging across the developed world and many governments are already making moves toward raising the age of retirement to try to cope with the potential explosion in extra costs to health and social services.

A study by Danish researchers last month showed that more than half of babies born in rich nations today will live to see their 100th birthdays -- a trend that means they are also very likely to have to work longer into old age.

Arguably the best option is to redesign working life for older workers to make it healthier and more satisfying than at present and...achieve improved occupational health and quality of life, increased productivity, and a larger proportion of the population in work, Westerlund and his colleagues wrote.

The study, published in The Lancet medical journal on Monday, used data from workers at a gas and electricity firm which operates throughout France. Compared with many employees worldwide, the workers retired early -- from age 55 -- and got good pensions of around 80 percent of their former salary.

But the researchers said the substantial improvements shown by most employees suggested the results could apply to a large proportion of workers in developed countries, particularly those with good social security provision after retirement.