An aging America reduces the economy’s growth — big time. That’s the startling conclusion of a new academic study, and if it withstands scholarly scrutiny, it could transform our national political and economic debate.

We’ve known for decades, of course, that the retirement of the huge baby-boom generation — coupled with low birthrates — would make the United States an older society. Similarly, we’ve known that this would squeeze the federal budget.

But the new study goes a giant step further, claiming that the very fact that the United States is an aging society weakens economic growth.

“The fraction of the United States population age 60 or over will increase by 21 percent between 2010 and 2020,” says the study. This aging shaves 1.2 percentage points off the economy’s present annual growth rate, the study estimates.

Although this seems small, it’s enormous. Consider the numbers. From the 1950s to 2007, the economy grew about 3 percent a year.

By contrast, annual growth since 2010 has averaged about 2 percent. But add in the 1.2 percent annual growth lost to aging, and we’re roughly at 3 percent growth again.

In effect, demographics rule. The theory’s added appeal is that it might apply globally, because almost all advanced countries are experiencing both aging populations and slower economic growth. This implies — but does not automatically prove — a common cause.

Still, it won’t be easy to convince other economists that aging explains most of the economic slowdown. Probably the theory will strike many as too simple.

“I start with a strong skepticism that one factor explains where we are,” says Brookings Institution economist Gary Burtless, who has also done research on the impact of aging.

Generally, aging poses two possible adverse economic effects. One is uncontroversial. As swarms of retirees leave the labor force, there are relatively fewer workers to support production. This hurts economic growth, but it represents only one-third of the slowdown, the study estimates.

The other two-thirds reflects reduced productivity; workers become less efficient. Not just older workers — all workers. That’s surprising, and there’s no clear answer as to why. This is the study’s weak point. The conclusion rests on data points that can’t be explained.

There are theories. It could be that as experienced workers retire, their positive effect on the work climate is lost. Although this is plausible, it’s also guesswork. It’s also partly undercut by Burtless’ research, which found that the most skilled older workers stay in their jobs longer.

On the whole, the study is bad news. One way that advanced societies can handle aging populations is through faster economic growth, which enables younger generations to pay the elderly’s benefits without sacrificing too much of their own incomes.

But if aging is a cause of slower economic growth — even if the impact is less than the study suggests — then this avenue is of limited help.

As a society, we need a better balance of obligation between the older and younger generations. Until now, policy has favored the elderly.

If slower economic growth is linked to aging, the competition for scarce funds will become even harder. It’s a dismal connection.

Robert Samuelson is a columnist with The Washington Post Writers Group.