Falling commodity prices and mixed corporate earnings helped push down Canada's main stock index Thursday, while U.S. stock markets also fell.

"It's a pretty earnings-driven market," said Ryan Crowther, a portfolio manager at Franklin Bissett Investment Management in Calgary.

"At either end of the spectrum you've got you've got certain companies that have surprised to the upside or the downside, and (are) influencing the TSX."

The mixed picture meant morning gains reversed as the day went on. 

The S&P/TSX Composite Index ended down 81.79 points, or 0.4 per cent, at 20,597.75 after trading as high as 20,821.66 earlier in the day. 

Losses among key subindexes were modest but across the board. 

The telecom index was down 1.4 per cent as Telus Corp. dropped 3.8 per cent after reporting results where earnings came in below expectations.

Health care was down 3.6 per cent as cannabis producer Canopy Growth Corp. fell 16.6 per cent after announcing layoffs and a restructuring as it reported earnings that also missed expectations.

Uranium producer Cameco Corp. saw its share price climb 4.6 per cent as investors welcomed its quarterly results and outlook for higher demand ahead.

Company earning results were also mixed in New York, where the Dow Jones Industrial Average closed down 249.13 points at 33,699.88. The S&P 500 Index was down 36.36 points at 4,081.50, while the Nasdaq Composite was down 120.94 points at 11,789.58. 

Overall, higher interest rates and other concerns are starting to show up in company performance, even if some are weathering it better, said Crowther.

"We've had some companies come through with surprising resilience in the face of emerging economic headwinds, but if you compare calendar Q4 to the previous couple of quarters, we're seeing more cases where this weakening environment is taking its toll on earnings."

While headwinds are growing, they're not yet fully showing up in some company valuations, he said. 

"Many equities do remain overvalued in our opinion, given the current environment. I'd expect that there's going to be opportunities for investors, as many companies face a challenging year and could see increased volatility in the weeks to come."

The Canadian dollar traded for 74.48 cents U.S. compared with 74.47 cents U.S. on Wednesday.

The March crude contract was down 41 cents at US$78.06 per barrel and the March natural gas contract was up 34 cents at US$2.43 per mmBTU.

The April gold contract was down US$12.20 at US$1,878.50 an ounce and the March copper contract was up six cents at US$4.10 a pound.