"We will have to learn to make do with a lot less in material things," says Gary Snodgrass, a 63-year-old health-care consultant in Placerville, Calif. The financial crisis, he says, slashed his retirement savings 40% and the value of his house by about half.

Banks, home buyers and bond issuers are all benefiting as the U.S. Federal Reserve holds short-term interest rates near zero to support a recovery. But for many of the 36 million Americans who will turn 65 over the next decade—and even for the 45 million who have another decade to go— the resulting low bond yields, combined with a volatile stock market, are making a dire retirement picture look even worse.

Low yields present retirees with a difficult choice: Accept the lower income offered by safer bonds, or take the risk of staying in the stock market. Either way, their predicament could put a long-term damper on the consumer spending that typically drives U.S. growth.

"If these rates stay as low as they are, then a lot more people are going to be hurting," says Jack Van Derhei, research director at the Employee Benefit Research Institute. The non-partisan outfit estimates that if current conditions persist, nearly three in five baby boomers will be at risk of running short of money in retirement. "There are going to be many luxury items that will simply have to be eliminated," for retirees to make ends meet.

Despite the market's rebound from the lows of 2009, nest eggs remain severely impaired. As of the first quarter of 2010, net household assets—homes, 401(k) plans, pension assets and other investments minus debts—stood at $54.6 trillion, down 18% from the end of 2007. That's an average of about $171,000 per person, much of which is concentrated in the hands of the wealthiest.

At the same time, the return people can hope to earn on their assets has fallen, particularly for those who switch into bonds or annuities to guarantee a fixed income. The average yield on U.S. government, corporate and mortgage bonds stands at about 2.4%, while stock-market valuations suggest a long-term return of about 6%. At those levels of return, some 59% of people aged 56 to 62 will be at risk of not having enough money to cover basic living and health-care costs in retirement, estimates Mr. Van Derhei. If market returns are higher—8.9% for stocks and 6.3% for bonds—the picture isn't a lot better: The percentage at risk falls to about 47%.

Before the recession hit, many economists assumed people would solve their retirement problems simply by staying in the work force longer. Now, "the recession has blown that idea out of the water," says Alicia Munnell, director of the Center for Retirement Research at Boston College and co-author of a 2008 book that advocated working longer.

Older workers, who typically fared better than their younger counterparts in recessions, have been hit just as hard by layoffs this time around. As a result, the fraction of people 65 or older who are working has leveled off after a long period of growth. As of July, it stood at 15.9%, down from 16.3% in mid-2008.

With the overall unemployment rate hovering at 9.5%, many older workers have now found themselves at the back of the line to return to the work force. "Many employers seem to think it is not worth their time or effort to train me in a position," says Kathleen McCabe, 59, a former apartment manager in Tulsa, Okla., who has been out of work since April 2009. "They assume I will leave for retirement soon."

The diminishing work prospects will require many older folks to make do with less—a discouraging outlook for firms hoping to sell them everything from restaurant meals to cars.

As of 2008, the latest data available, people aged 65 to 74 were spending 12.3% less than they did ten years earlier, in inflation-adjusted terms. They cut spending on cars and trucks by 46%, household furnishings by 35% and dining out by 27%. At the same time, they spent 75% more on health care and 131% more on health insurance.

The impact isn't limited to people on the verge of retiring. Younger people, too, will have to reduce consumption now to save enough money to get by in retirement. That's one reason Richard Berner, chief U.S. economist at Morgan Stanley in New York, estimates that even after the economy recovers, consumer spending will grow at an annual, inflation-adjusted rate of about 2% to 2.5% in the long term, compared to an average of 3.6% in the ten years leading up to the last recession.

Policy makers have more immediate concerns, such as how to create jobs for the nearly 15 million unemployed. The predicament of retirees, though, demonstrates how policy decisions—for example, on whether to stimulate the economy through interest rates or government spending—can have repercussions for many years to come.