(Bloomberg) -- The world’s working-age population is shrinkingfaster than expected, leaving fewer people to support a growingnumber of seniors, according to the Bloomberg Sunset Index.

Related: Lifespan falls in U.S., weathly livedecade longer than others

Conventional measures of old-age dependency calculate the ratioof people ages 65 and older with those of working age: 15 to64.

But many people stop working well before 65: Men in 66 percentof the 177 countries Bloomberg evaluated and women in 78 percentcan begin receiving retirement benefits earlier.

Related: 2017's 10 best states to retirein

So the Bloomberg index calculates dependency based on eachcountry’s statutory pensionable age, revealing substantialdifferences in some places with 2016 estimates from organizationsincluding the World Bank and United Nations.

Nigeria, with a statutory pensionable age of 50, has only 4.8workers supporting each senior, compared with 19.4 as indicated byconventional measures. Russia has 2.4 instead of 5.1, and Colombiahas 4.5 instead of 9.4.

Related: Longer lifespans too expensive, workersfear

As seniors increasingly outnumber people still in the workforce,pressures rise on investment pools, medical systems and funds tobuild economies for future generations.

“The demographics cannot be ignored, but there are solutions,”said Suzanne Kunkel, director of the Scripps GerontologyCenter at Miami University in Oxford, Ohio. “Those solutionsneed to be cultural, political, economic. There is no magic answer.The reality is China will deal with it differently than Italy.”

Asia could be facing the toughest choices in allocatingresources. The Asia Pacific Risk Center estimates the region’selderly population will rise 71 percent by 2030, compared with 55percent in North America and 31 percent in Europe.

The retirement age in China -- with almost 22 percent of theworld’s 65-plus population -- is 60 for men and 55 for women. TheBloomberg Sunset Index shows 3.5 workers supporting each seniorthere; conventional calculations indicate 7.3.

Seniors in France, where the retirement age is 61.6, are theleast supported, with a ratio of about two workers to each retiree,the index shows. In the U.S., the ratio is 4.4 to one.

Americans can start receiving Social Security at 62, with asliding scale for full retirement benefits from 65 to 67, dependingon the year of birth. In June, the Social Security Administrationestimated the program’s trust fund will run out of money in 2034,though the timeline could be extended by raising the retirement ageeven more.

Related: Age longevity changes everything aboutretirement planning

“There are other-than-alarmist views about population aging,”said David Ekerdt, director of the Gerontology Center at theUniversity of Kansas. “Advanced economies face rather differentchallenges depending on the social provisions they have promisedand the declines in fertility that have occurred in thesenations.”

The U.S., for example, has “very high health-care costs for allcitizens,” he said. “I would also say, politically, that it’s alarge leap to assume that social spending, if reduced for onegroup, would be applied to another group.”

Other countries also raised retirement thresholds in the pastfour years. In France, it’s now 61.58, up from 60. For Greek men,it’s 67 instead of 65. For Italian women, it’s 65.58, up from62.

The National Social Security Fund in Kenya, the country’slargest pension fund, is turning to private equity and seekinginvestments abroad to boost returns. The Bloomberg index shows 11.7workers supporting each senior there, compared with 19.4 byconventional calculations.

In Japan, where many people work beyond the statutorypensionable age of 65, payments from the government-run pensionsystem account for more than 10 percent of gross domesticproduct.

In December, parliament approved a bill allowing for smallerpayments if consumer prices and wages decline. Taking it a stepfurther, Japan replaced silver sake cups it gives new centenarianswith cheaper silver-plated ones.

Copyright 2018 Bloomberg. All rightsreserved. This material may not be published, broadcast, rewritten,or redistributed.