Podcasts have grown significantly more popular since iTunes started listing the audio and video downloads last year, according to a report released this week by Nielsen Analytics.

The study indicates that the growth of podcasts could have significant effects on advertising models and radio listener numbers in the near future, as web users turn away from traditional media for online news, entertainment and political commentary.

The report, “The Economics of Podcasting”, found that more than 6 per cent of US adults, or nearly 9m web users, have downloaded at least one podcast in the last month. Of those, about 10 per cent are “heavy users”, downloading eight or more podcasts weekly. Most podcast listeners download between one and three shows per week.

These findings, issued on Thursday, closely mirror another Nielsen report released July 12, which found that 6.6 per cent of the US adult online population, or 9.2m people, have downloaded at least one audio podcast in the last month. That study was conducted by Nielsen/NetRatings.

About 60 per cent of the “regular” or “active” podcast downloaders - the vast majority of whom are men - fast forward through commercials in their podcasts, reflecting a trend seen in other media.

Larry Gerbrandt, general manager and senior vice-president at Nielsen Analytics, said that “the onus is on the advertiser” to incorporate ads into podcasts through sponsorships or product placement.

Radio companies will need to embrace podcasts as downloads continue to rise. The Nielsen revealed that 38 per cent of “active” podcasters say they now listen to the radio less often than before beginning to download podcasts.

“This is not the death knell for the industry,” Mr Gerbrandt said of radio, but warned that as more cars became iPod-compatible and therefore podcast-compatible, radio would face even greater competition.

At his latest count, about three weeks ago, iTunes, created and owned by Apple Computer, listed 60,000 different podcasts.