The United States ranks 19th in the quality of retirement available to senior citizens, according to the Natixis Global Retirement Index released Thursday.

The ranking is due mainly to the better social and health-care safety nets that exist in European countries that outranked the United States, Natixis says.

The study suggests that Americans will need to pick up a bigger share of their own retirement costs, especially as the number of retirees grows and the government’s ability to support them fades. The study was conducted by Natixis' Durable Portfolio Research Center. The firm oversees $779 billion, including retirement assets for institutions and individuals.

The study ranked 150 countries on factors such as health care, finances, material comfort and quality of life. The Durable Portfolio Research Center conducts research on risk management, asset allocation and other investment issues.

“Citizens of other industrialized nations can rely on strong social safety nets in old age, at least for now,” says John Hailer, Natixis' president and CEO. “In the U.S., we encourage workers to plan, save and invest, and promote policies that help them meet their future needs.”

Norway, Switzerland, Luxembourg, Sweden and Austria top the list. Others that beat the United States include the Czech Republic, Japan, Slovenia and Slovakia. The United Kingdom comes in just under the United States.

While the U.S. leads the world in per capita health spending, individuals are still required to pay a portion of this expense on their own, the report says. That leaves many health costs in the hands of retirees and takes resources away from their other needs.

In contrast, Western European nations, backed by robust health care and retiree social programs, dominate the top of the rankings, the report notes. By 2050, the ratio of working-age people to those over 65 in the U.S. is expected to drop from 5-1 to 2.8-1, which will diminish the government’s ability to finance programs such as Social Security and Medicare.

The economic downturn has also taken a major toll on retirement savings. Fifty-three percent of American workers 30 and older are on a path that will leave them unprepared for retirement, up significantly from 38 percent just two years ago, the study says.

To meet their retirement objectives, investors should employ a broad range of asset classes. A diversified portfolio can help investors temper short-term volatility and pursue long-term growth, Natixis says.