Women stand inside a beadhouse, a home for the elderly, in Xining, capital of northwestern China's Qinghai province October 26, 2006. REUTERS/Stringer

The world's population of older people is growing at the fastest rate ever seen and the old will soon outnumber the young for the first time, U.S. researchers reported on Monday.

An aging population will push up pension and healthcare costs, forcing major increases in public spending that could slow economic growth in rich and poor countries.

The number of people 65 and older hit about 506 million as of midyear 2008, according to the U.S. Census Bureau. This will double to 1.3 billion by 2040, accounting for 14 percent of the total global population.

People aged 65 and over will soon outnumber children under age 5 for the first time in history, said the report put together by Kevin Kinsella and Wan He of the U.S. Census Bureau.

Aging is affecting every country in every part of the world, said Richard Suzman of the National Institute of Aging, which commissioned the report. While there are important differences between developed and developing countries, global aging is changing the social and economic nature of the planet and presenting difficult challenges.

The report found that people aged 80 and older are the fastest growing portion of the total population in many countries. Globally, this oldest old population is projected to increase by 233 percent between 2008 and 2040.

This could strain their children and grandchildren.

Shrinking ratios of workers to pensioners and people spending a larger portion of their lives in retirement increasingly tax existing health and pension systems, the report said.

In a few years' time, just after 2010, the numbers and proportions of older people (especially the oldest old) will begin to rise rapidly in most developed and many developing countries, it added.

The increase is primarily the result of high fertility levels after World War II and secondarily, but increasingly, the result of reduced death rates at older ages.

Chronic diseases such as heart disease and cancer remain the top killers, especially of the elderly. This in turn means huge expense for healthcare systems.

And this will not only happen in the industrialized world.

By 2040, today's developing countries are likely to be home to more than 1 billion people aged 65 and over, 76 percent of the projected world total, the report reads.

Each month, 870,000 people turn 65. In 10 years, 1.9 million people will celebrate their 65th birthdays each month.

If countries and businesses plan right, an aging population could create opportunities for economic growth, the report said.But it also cited a 2006 European Commission report that found the costs of pensions, healthcare and long-term care will force major increases in public spending and force down gross domestic product growth rates.

And in the absence of policy changes, the potential EU economic growth rate would be cut in half by 2030, the report cautioned.