(Adds comment from spokesperson)

By Trevor Hunnicutt

NEW YORK, Feb 28 (Reuters) - BlackRock Inc, the world's largest asset manager, on Wednesday said that commentary by third parties suggesting possible adverse impacts from the growth in index investing could pose a risk to its business.

"As a leader in the index investing and asset management industry, BlackRock has been the subject of third-party commentary citing concerns about the growth of index investing," the company said in a new risk disclosure its annual report, filed with the U.S. Securities and Exchange Commission.

"If the conclusions advanced by such commentators were to gain traction or result in the enactment of policy measures that place limits on asset managers, BlackRock's business operations, reputation or financial condition may be adversely affected," it said.

A spokesperson for BlackRock said, "Similar to many other public companies we take a conservative approach in disclosing 'risk factors' to shareholders. The dialogue around this topic is still extremely preliminary."

Most publicly traded U.S. companies are required to file annual 10-K reports with securities regulators, disclosing among other details their most essential risks in plain language.

Criticism of index investing is not new, but BlackRock's highlighting a particular thread of concern as a primary risk factor in this way is. The company manages $1.8 trillion in iShares-brand exchange-traded funds (ETFs), most of which track an index, and another $2.4 trillion in non-ETF index funds.

BlackRock zeroed in on one argument about index investing that says index funds' "common ownership" of several companies in a single market segment reduces competition between those companies, imposing a cost on society that may need to be regulated. The asset management company and other researchers have disputed academic studies coming to that conclusion.

BlackRock also referenced commentary about the risk of index investing "to distort investment flows, create stock price bubbles, or conversely, exacerbate a decline in market prices." (Reporting by Trevor Hunnicutt Editing by Leslie Adler and Sunil Nair)