The NFL, which holds its Super Bowl on Sunday, is enjoying a significant surge in global interest with China and Russia leading the way, according to a study by a leading sports marketing research company.

The report by Germany-based Repucom found interest in the league rising in several key markets with Russia having the highest percentage of the population focused on the league.

The report says 13.3 percent of Russians are fans of the NFL, with a growth of 5.3 percent in the past year leading to a total of 10.38 million fans.

The growth of the NFL in China in the past year is the biggest in terms of population size.

Since 2013 interest in the NFL among the Chinese population has jumped from 1.7 to 7.9 percent -- meaning an extra 31 million people have an interest in the sport there.

The upward trend is also evident in South America with Brazil seeing a rise of 3.3 million in NFL fans.

The NFL's biggest international focus -- and one of its key successes -- has been in the United Kingdom where three regular season games were held in the past year.

Repucom found interest had grown from 8.1 percent in 2012 to 12.3 percent, adding an extra 1.86 million NFL fans.

The UK is second only to Russia in terms of percentage of the population now following the game in some way.

GROWING TREND

"This growing trend should be a welcome sight for the NFL," said Glenn Lovett, president of global strategy at Repucom.

"More engaged fans bring additional revenue and growth opportunities across their business. They provide the league with a better offering to commercial partners in the U.S. and overseas whilst increasing stability for the game," he added.

The NFL's video distribution has become more sophisticated in recent years where as well as deals with television broadcasters, the league also offers 'Game Pass', a subscription online service offering various packages for live games.

In the U.K. the NFL has a broadcast deal with subscription network Sky Sports and also free-to-air Channel Four, who also produce their own weekly highlights show.

David Tossell, Director of Public Affairs for NFL International, Europe, said the research showed similar trends to the league's own in-house studies.

He said the NFL's focus internationally had been on "exposing people to the sport, building the support and growing the fan base.

"The Game Pass product means that even in markets without a television deal we are able to promote and expose the sport around the world," he told Reuters.