The U.S. economy expanded at a 4.1 percent annual rate in the third quarter, a significantly faster pace than first thought and its strongest showing since the end of 2011, the Bureau of Economic Analysis said Friday.

After each quarter, the agency spends the next three months reporting and revising its figures on gross domestic product growth.

Earlier, BEA said it thought GDP grew at a 3.6 percent annual rate from the end of June through September. That was up from its initial estimate of 2.8 percent.

Now it's saying growth topped 4 percent.

What's led to the upward revisions? "Stronger consumer spending, primarily in the area of health care," The Associated Press reports.

At 4.1 percent, growth was the strongest since the 4.9 percent gain in fourth-quarter 2011. Growth was also up from recent quarters. This year began with weak, 1.1 percent growth in the first quarter and was followed by a 2.5 percent gain in the second.

Looking ahead, MarketWatch writes, economists caution that growth could slow — particularly if companies have trouble selling some of the goods they've recently added to inventories.

There have also been some signs, as we reported Thursday, that one of the economy's stronger sectors in recent months — housing — may be cooling off due to slightly higher mortgage rates and a tight supply of homes.

Still, economist tells our Newscast Desk that the GDP report suggests "the economy, based on a lot of different factors, is starting to show some improvement."

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