A working paper published Monday by the National Bureau of Economic Research, which studied the effects of the aging of the American population on economic growth, found that old people could be the reason the economy has been more sluggish the last few years than expected. The researchers found that the U.S.’s aging population is cutting as much as 1.2 percentage points off of per capita GDP growth, which is a huge amount if you think of how slow GDP has been growing recently.

So how did these economists come to this conclusion? By comparing the growth rate of such states as Maine, Oregan, and South Carolina that during the 2000 to 2010 period were aging as quickly as the U.S. is now to the overall U.S. economy. They also control for migration, i.e. younger workers leaving states with weaker economies.

In one sense, this is not a surprising result because the growth of the labor force is a key determinant of economic growth. (This is why economists tend to support increased immigration, for instance.) But what is equally surprising about this study is that the researchers find that the majority of the slowdown in per capita economic growth is the result in declines in labor force productivity growth, not just the fact that the number of workers in the economy is slowing due to more retirees.

Why exactly a change in demographic makeup is causing a decline in labor force productivity growth is unclear, but the authors hypothesize that it could be the result of the most productive older workers retiring first. If this is the case, then the decline in productivity growth could be the result of their being less of a “spillover” effect, whereby younger workers gain skills through working in proximity to productive older workers.

Regardless of the reason, the results of the study should be alarming. The authors of the report are predicting that demographic effects will continue to drag down American growth for the next fifteen years, representing hundreds of billions of dollars in lost potential wealth. While a portion of the political class has been honest about the need to reform entitlement spending as a result of an aging population, there have been few public figures who have argued that we need to reckon with the idea that changing demographics will result in significantly slower growth overall, and therefore require average Americans to reduce their own expectations for how quickly their own financial situations will improve over time.

What we’ve had instead is politicians arguing that the lack of growth we have seen of late is the result of their particular economic agenda not being passed into law, and that we are just one election away from regaining economic glory, either by radically cutting taxes or boosting spending. But the true demographic facts suggest we won’t see all of that until at least another generation.